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| 4 | <head><title>Vorbis I specification</title>
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| 9 | <meta name="src" content="Vorbis_I_spec.tex">
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| 11 | </head><body
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| 12 | >
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| 13 | <div class="maketitle">
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| 14 |
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| 15 |
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| 16 |
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| 17 |
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| 18 | <h2 class="titleHead">Vorbis I specification</h2>
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| 19 | <div class="author" ><span
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| 20 | class="cmr-17">Xiph.Org Foundation</span></div><br />
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| 21 | <div class="date" ><span
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| 22 | class="cmr-17">July 4, 2020</span></div>
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| 23 | </div>
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| 24 | <h3 class="likesectionHead"><a
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| 25 | id="x1-1000"></a>Contents</h3>
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| 26 | <div class="tableofcontents">
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| 27 |  <span class="sectionToc" >1 <a
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| 28 | href="#x1-20001" id="QQ2-1-2">Introduction and Description</a></span>
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| 29 | <br />  <span class="subsectionToc" >1.1 <a
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| 30 | href="#x1-30001.1" id="QQ2-1-3">Overview</a></span>
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| 31 | <br />   <span class="subsubsectionToc" >1.1.1 <a
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| 32 | href="#x1-40001.1.1" id="QQ2-1-4">Application</a></span>
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| 33 | <br />   <span class="subsubsectionToc" >1.1.2 <a
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| 34 | href="#x1-50001.1.2" id="QQ2-1-5">Classification</a></span>
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| 35 | <br />   <span class="subsubsectionToc" >1.1.3 <a
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| 36 | href="#x1-60001.1.3" id="QQ2-1-6">Assumptions</a></span>
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| 37 | <br />   <span class="subsubsectionToc" >1.1.4 <a
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| 38 | href="#x1-70001.1.4" id="QQ2-1-7">Codec Setup and Probability Model</a></span>
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| 39 | <br />   <span class="subsubsectionToc" >1.1.5 <a
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| 40 | href="#x1-90001.1.5" id="QQ2-1-9">Format Specification</a></span>
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| 41 | <br />   <span class="subsubsectionToc" >1.1.6 <a
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| 42 | href="#x1-100001.1.6" id="QQ2-1-10">Hardware Profile</a></span>
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| 43 | <br />  <span class="subsectionToc" >1.2 <a
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| 44 | href="#x1-110001.2" id="QQ2-1-11">Decoder Configuration</a></span>
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| 45 | <br />   <span class="subsubsectionToc" >1.2.1 <a
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| 46 | href="#x1-120001.2.1" id="QQ2-1-13">Global Config</a></span>
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| 47 | <br />   <span class="subsubsectionToc" >1.2.2 <a
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| 48 | href="#x1-130001.2.2" id="QQ2-1-14">Mode</a></span>
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| 49 | <br />   <span class="subsubsectionToc" >1.2.3 <a
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| 50 | href="#x1-140001.2.3" id="QQ2-1-15">Mapping</a></span>
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| 51 |
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| 52 |
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| 53 |
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| 54 | <br />   <span class="subsubsectionToc" >1.2.4 <a
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| 55 | href="#x1-150001.2.4" id="QQ2-1-16">Floor</a></span>
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| 56 | <br />   <span class="subsubsectionToc" >1.2.5 <a
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| 57 | href="#x1-160001.2.5" id="QQ2-1-17">Residue</a></span>
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| 58 | <br />   <span class="subsubsectionToc" >1.2.6 <a
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| 59 | href="#x1-170001.2.6" id="QQ2-1-18">Codebooks</a></span>
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| 60 | <br />  <span class="subsectionToc" >1.3 <a
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| 61 | href="#x1-180001.3" id="QQ2-1-19">High-level Decode Process</a></span>
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| 62 | <br />   <span class="subsubsectionToc" >1.3.1 <a
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| 63 | href="#x1-190001.3.1" id="QQ2-1-20">Decode Setup</a></span>
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| 64 | <br />   <span class="subsubsectionToc" >1.3.2 <a
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| 65 | href="#x1-230001.3.2" id="QQ2-1-24">Decode Procedure</a></span>
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| 66 | <br /> <span class="sectionToc" >2 <a
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| 67 | href="#x1-360002" id="QQ2-1-39">Bitpacking Convention</a></span>
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| 68 | <br />  <span class="subsectionToc" >2.1 <a
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| 69 | href="#x1-370002.1" id="QQ2-1-40">Overview</a></span>
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| 70 | <br />   <span class="subsubsectionToc" >2.1.1 <a
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| 71 | href="#x1-380002.1.1" id="QQ2-1-41">octets, bytes and words</a></span>
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| 72 | <br />   <span class="subsubsectionToc" >2.1.2 <a
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| 73 | href="#x1-390002.1.2" id="QQ2-1-42">bit order</a></span>
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| 74 | <br />   <span class="subsubsectionToc" >2.1.3 <a
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| 75 | href="#x1-400002.1.3" id="QQ2-1-43">byte order</a></span>
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| 76 | <br />   <span class="subsubsectionToc" >2.1.4 <a
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| 77 | href="#x1-410002.1.4" id="QQ2-1-44">coding bits into byte sequences</a></span>
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| 78 | <br />   <span class="subsubsectionToc" >2.1.5 <a
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| 79 | href="#x1-420002.1.5" id="QQ2-1-45">signedness</a></span>
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| 80 | <br />   <span class="subsubsectionToc" >2.1.6 <a
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| 81 | href="#x1-430002.1.6" id="QQ2-1-46">coding example</a></span>
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| 82 | <br />   <span class="subsubsectionToc" >2.1.7 <a
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| 83 | href="#x1-440002.1.7" id="QQ2-1-47">decoding example</a></span>
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| 84 | <br />   <span class="subsubsectionToc" >2.1.8 <a
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| 85 | href="#x1-450002.1.8" id="QQ2-1-48">end-of-packet alignment</a></span>
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| 86 | <br />   <span class="subsubsectionToc" >2.1.9 <a
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| 87 | href="#x1-460002.1.9" id="QQ2-1-49">reading zero bits</a></span>
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| 88 | <br /> <span class="sectionToc" >3 <a
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| 89 | href="#x1-470003" id="QQ2-1-50">Probability Model and Codebooks</a></span>
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| 90 | <br />  <span class="subsectionToc" >3.1 <a
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| 91 | href="#x1-480003.1" id="QQ2-1-51">Overview</a></span>
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| 92 | <br />   <span class="subsubsectionToc" >3.1.1 <a
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| 93 | href="#x1-490003.1.1" id="QQ2-1-52">Bitwise operation</a></span>
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| 94 | <br />  <span class="subsectionToc" >3.2 <a
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| 95 | href="#x1-500003.2" id="QQ2-1-53">Packed codebook format</a></span>
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| 96 | <br />   <span class="subsubsectionToc" >3.2.1 <a
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| 97 | href="#x1-510003.2.1" id="QQ2-1-54">codebook decode</a></span>
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| 98 | <br />  <span class="subsectionToc" >3.3 <a
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| 99 | href="#x1-580003.3" id="QQ2-1-63">Use of the codebook abstraction</a></span>
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| 100 | <br /> <span class="sectionToc" >4 <a
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| 101 | href="#x1-590004" id="QQ2-1-64">Codec Setup and Packet Decode</a></span>
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| 102 | <br />  <span class="subsectionToc" >4.1 <a
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| 103 | href="#x1-600004.1" id="QQ2-1-65">Overview</a></span>
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| 104 | <br />  <span class="subsectionToc" >4.2 <a
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| 105 | href="#x1-610004.2" id="QQ2-1-66">Header decode and decode setup</a></span>
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| 106 | <br />   <span class="subsubsectionToc" >4.2.1 <a
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| 107 | href="#x1-620004.2.1" id="QQ2-1-67">Common header decode</a></span>
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| 108 | <br />   <span class="subsubsectionToc" >4.2.2 <a
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| 109 | href="#x1-630004.2.2" id="QQ2-1-68">Identification header</a></span>
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| 110 | <br />   <span class="subsubsectionToc" >4.2.3 <a
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| 111 | href="#x1-640004.2.3" id="QQ2-1-69">Comment header</a></span>
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| 112 |
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| 113 |
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| 114 |
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| 115 | <br />   <span class="subsubsectionToc" >4.2.4 <a
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| 116 | href="#x1-650004.2.4" id="QQ2-1-70">Setup header</a></span>
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| 117 | <br />  <span class="subsectionToc" >4.3 <a
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| 118 | href="#x1-720004.3" id="QQ2-1-78">Audio packet decode and synthesis</a></span>
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| 119 | <br />   <span class="subsubsectionToc" >4.3.1 <a
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| 120 | href="#x1-730004.3.1" id="QQ2-1-79">packet type, mode and window decode</a></span>
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| 121 | <br />   <span class="subsubsectionToc" >4.3.2 <a
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| 122 | href="#x1-740004.3.2" id="QQ2-1-80">floor curve decode</a></span>
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| 123 | <br />   <span class="subsubsectionToc" >4.3.3 <a
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| 124 | href="#x1-750004.3.3" id="QQ2-1-81">nonzero vector propagate</a></span>
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| 125 | <br />   <span class="subsubsectionToc" >4.3.4 <a
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| 126 | href="#x1-760004.3.4" id="QQ2-1-82">residue decode</a></span>
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| 127 | <br />   <span class="subsubsectionToc" >4.3.5 <a
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| 128 | href="#x1-770004.3.5" id="QQ2-1-83">inverse coupling</a></span>
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| 129 | <br />   <span class="subsubsectionToc" >4.3.6 <a
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| 130 | href="#x1-780004.3.6" id="QQ2-1-84">dot product</a></span>
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| 131 | <br />   <span class="subsubsectionToc" >4.3.7 <a
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| 132 | href="#x1-790004.3.7" id="QQ2-1-85">inverse MDCT</a></span>
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| 133 | <br />   <span class="subsubsectionToc" >4.3.8 <a
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| 134 | href="#x1-800004.3.8" id="QQ2-1-86">overlap_add</a></span>
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| 135 | <br />   <span class="subsubsectionToc" >4.3.9 <a
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| 136 | href="#x1-810004.3.9" id="QQ2-1-87">output channel order</a></span>
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| 137 | <br /> <span class="sectionToc" >5 <a
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| 138 | href="#x1-820005" id="QQ2-1-88">comment field and header specification</a></span>
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| 139 | <br />  <span class="subsectionToc" >5.1 <a
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| 140 | href="#x1-830005.1" id="QQ2-1-89">Overview</a></span>
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| 141 | <br />  <span class="subsectionToc" >5.2 <a
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| 142 | href="#x1-840005.2" id="QQ2-1-90">Comment encoding</a></span>
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| 143 | <br />   <span class="subsubsectionToc" >5.2.1 <a
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| 144 | href="#x1-850005.2.1" id="QQ2-1-91">Structure</a></span>
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| 145 | <br />   <span class="subsubsectionToc" >5.2.2 <a
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| 146 | href="#x1-860005.2.2" id="QQ2-1-92">Content vector format</a></span>
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| 147 | <br />   <span class="subsubsectionToc" >5.2.3 <a
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| 148 | href="#x1-890005.2.3" id="QQ2-1-95">Encoding</a></span>
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| 149 | <br /> <span class="sectionToc" >6 <a
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| 150 | href="#x1-900006" id="QQ2-1-96">Floor type 0 setup and decode</a></span>
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| 151 | <br />  <span class="subsectionToc" >6.1 <a
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| 152 | href="#x1-910006.1" id="QQ2-1-97">Overview</a></span>
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| 153 | <br />  <span class="subsectionToc" >6.2 <a
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| 154 | href="#x1-920006.2" id="QQ2-1-98">Floor 0 format</a></span>
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| 155 | <br />   <span class="subsubsectionToc" >6.2.1 <a
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| 156 | href="#x1-930006.2.1" id="QQ2-1-99">header decode</a></span>
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| 157 | <br />   <span class="subsubsectionToc" >6.2.2 <a
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| 158 | href="#x1-940006.2.2" id="QQ2-1-100">packet decode</a></span>
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| 159 | <br />   <span class="subsubsectionToc" >6.2.3 <a
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| 160 | href="#x1-950006.2.3" id="QQ2-1-101">curve computation</a></span>
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| 161 | <br /> <span class="sectionToc" >7 <a
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| 162 | href="#x1-970007" id="QQ2-1-103">Floor type 1 setup and decode</a></span>
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| 163 | <br />  <span class="subsectionToc" >7.1 <a
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| 164 | href="#x1-980007.1" id="QQ2-1-104">Overview</a></span>
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| 165 | <br />  <span class="subsectionToc" >7.2 <a
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| 166 | href="#x1-990007.2" id="QQ2-1-105">Floor 1 format</a></span>
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| 167 | <br />   <span class="subsubsectionToc" >7.2.1 <a
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| 168 | href="#x1-1000007.2.1" id="QQ2-1-106">model</a></span>
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| 169 | <br />   <span class="subsubsectionToc" >7.2.2 <a
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| 170 | href="#x1-1010007.2.2" id="QQ2-1-111">header decode</a></span>
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| 171 | <br />   <span class="subsubsectionToc" >7.2.3 <a
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| 172 | href="#x1-1020007.2.3" id="QQ2-1-112">packet decode</a></span>
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| 173 |
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| 174 |
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| 175 |
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| 176 | <br />   <span class="subsubsectionToc" >7.2.4 <a
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| 177 | href="#x1-1030007.2.4" id="QQ2-1-113">curve computation</a></span>
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| 178 | <br /> <span class="sectionToc" >8 <a
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| 179 | href="#x1-1040008" id="QQ2-1-114">Residue setup and decode</a></span>
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| 180 | <br />  <span class="subsectionToc" >8.1 <a
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| 181 | href="#x1-1050008.1" id="QQ2-1-115">Overview</a></span>
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| 182 | <br />  <span class="subsectionToc" >8.2 <a
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| 183 | href="#x1-1060008.2" id="QQ2-1-116">Residue format</a></span>
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| 184 | <br />  <span class="subsectionToc" >8.3 <a
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| 185 | href="#x1-1070008.3" id="QQ2-1-118">residue 0</a></span>
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| 186 | <br />  <span class="subsectionToc" >8.4 <a
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| 187 | href="#x1-1080008.4" id="QQ2-1-119">residue 1</a></span>
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| 188 | <br />  <span class="subsectionToc" >8.5 <a
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| 189 | href="#x1-1090008.5" id="QQ2-1-120">residue 2</a></span>
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| 190 | <br />  <span class="subsectionToc" >8.6 <a
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| 191 | href="#x1-1100008.6" id="QQ2-1-122">Residue decode</a></span>
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| 192 | <br />   <span class="subsubsectionToc" >8.6.1 <a
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| 193 | href="#x1-1110008.6.1" id="QQ2-1-123">header decode</a></span>
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| 194 | <br />   <span class="subsubsectionToc" >8.6.2 <a
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| 195 | href="#x1-1120008.6.2" id="QQ2-1-124">packet decode</a></span>
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| 196 | <br />   <span class="subsubsectionToc" >8.6.3 <a
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| 197 | href="#x1-1130008.6.3" id="QQ2-1-125">format 0 specifics</a></span>
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| 198 | <br />   <span class="subsubsectionToc" >8.6.4 <a
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| 199 | href="#x1-1140008.6.4" id="QQ2-1-126">format 1 specifics</a></span>
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| 200 | <br />   <span class="subsubsectionToc" >8.6.5 <a
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| 201 | href="#x1-1150008.6.5" id="QQ2-1-127">format 2 specifics</a></span>
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| 202 | <br /> <span class="sectionToc" >9 <a
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| 203 | href="#x1-1160009" id="QQ2-1-128">Helper equations</a></span>
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| 204 | <br />  <span class="subsectionToc" >9.1 <a
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| 205 | href="#x1-1170009.1" id="QQ2-1-129">Overview</a></span>
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| 206 | <br />  <span class="subsectionToc" >9.2 <a
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| 207 | href="#x1-1180009.2" id="QQ2-1-130">Functions</a></span>
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| 208 | <br />   <span class="subsubsectionToc" >9.2.1 <a
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| 209 | href="#x1-1190009.2.1" id="QQ2-1-131">ilog</a></span>
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| 210 | <br />   <span class="subsubsectionToc" >9.2.2 <a
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| 211 | href="#x1-1200009.2.2" id="QQ2-1-132">float32_unpack</a></span>
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| 212 | <br />   <span class="subsubsectionToc" >9.2.3 <a
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| 213 | href="#x1-1210009.2.3" id="QQ2-1-133">lookup1_values</a></span>
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| 214 | <br />   <span class="subsubsectionToc" >9.2.4 <a
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| 215 | href="#x1-1220009.2.4" id="QQ2-1-134">low_neighbor</a></span>
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| 216 | <br />   <span class="subsubsectionToc" >9.2.5 <a
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| 217 | href="#x1-1230009.2.5" id="QQ2-1-135">high_neighbor</a></span>
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| 218 | <br />   <span class="subsubsectionToc" >9.2.6 <a
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| 219 | href="#x1-1240009.2.6" id="QQ2-1-136">render_point</a></span>
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| 220 | <br />   <span class="subsubsectionToc" >9.2.7 <a
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| 221 | href="#x1-1250009.2.7" id="QQ2-1-137">render_line</a></span>
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| 222 | <br /> <span class="sectionToc" >10 <a
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| 223 | href="#x1-12600010" id="QQ2-1-138">Tables</a></span>
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| 224 | <br />  <span class="subsectionToc" >10.1 <a
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| 225 | href="#x1-12700010.1" id="QQ2-1-139">floor1_inverse_dB_table</a></span>
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| 226 | <br /> <span class="sectionToc" >A <a
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| 227 | href="#x1-128000A" id="QQ2-1-140">Embedding Vorbis into an Ogg stream</a></span>
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| 228 | <br />  <span class="subsectionToc" >A.1 <a
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| 229 | href="#x1-129000A.1" id="QQ2-1-141">Overview</a></span>
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| 230 | <br />   <span class="subsubsectionToc" >A.1.1 <a
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| 231 | href="#x1-130000A.1.1" id="QQ2-1-142">Restrictions</a></span>
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| 232 | <br />   <span class="subsubsectionToc" >A.1.2 <a
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| 233 | href="#x1-131000A.1.2" id="QQ2-1-143">MIME type</a></span>
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| 234 |
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| 235 |
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| 236 |
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| 237 | <br />  <span class="subsectionToc" >A.2 <a
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| 238 | href="#x1-132000A.2" id="QQ2-1-144">Encapsulation</a></span>
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| 239 | <br /> <span class="sectionToc" >B <a
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| 240 | href="#x1-134000B" id="QQ2-1-146">Vorbis encapsulation in RTP</a></span>
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|---|
| 241 | </div>
|
|---|
| 242 |
|
|---|
| 243 |
|
|---|
| 244 |
|
|---|
| 245 | <h3 class="sectionHead"><span class="titlemark">1. </span> <a
|
|---|
| 246 | id="x1-20001"></a>Introduction and Description</h3>
|
|---|
| 247 | <!--l. 5--><p class="noindent" >
|
|---|
| 248 | <h4 class="subsectionHead"><span class="titlemark">1.1. </span> <a
|
|---|
| 249 | id="x1-30001.1"></a>Overview</h4>
|
|---|
| 250 | <!--l. 7--><p class="noindent" >This document provides a high level description of the Vorbis codec’s construction. A bit-by-bit
|
|---|
| 251 | specification appears beginning in <a
|
|---|
| 252 | href="#x1-590004">section 4</a>, “<a
|
|---|
| 253 | href="#x1-590004">Codec Setup and Packet Decode<!--tex4ht:ref: vorbis:spec:codec --></a>”. The later
|
|---|
| 254 | sections assume a high-level understanding of the Vorbis decode process, which is provided
|
|---|
| 255 | here.
|
|---|
| 256 | <!--l. 14--><p class="noindent" >
|
|---|
| 257 | <h5 class="subsubsectionHead"><span class="titlemark">1.1.1. </span> <a
|
|---|
| 258 | id="x1-40001.1.1"></a>Application</h5>
|
|---|
| 259 | <!--l. 15--><p class="noindent" >Vorbis is a general purpose perceptual audio CODEC intended to allow maximum encoder
|
|---|
| 260 | flexibility, thus allowing it to scale competitively over an exceptionally wide range of bitrates. At
|
|---|
| 261 | the high quality/bitrate end of the scale (CD or DAT rate stereo, 16/24 bits) it is in the same
|
|---|
| 262 | league as MPEG-2 and MPC. Similarly, the 1.0 encoder can encode high-quality CD and DAT
|
|---|
| 263 | rate stereo at below 48kbps without resampling to a lower rate. Vorbis is also intended for lower
|
|---|
| 264 | and higher sample rates (from 8kHz telephony to 192kHz digital masters) and a range of channel
|
|---|
| 265 | representations (monaural, polyphonic, stereo, quadraphonic, 5.1, ambisonic, or up to 255
|
|---|
| 266 | discrete channels).
|
|---|
| 267 | <!--l. 28--><p class="noindent" >
|
|---|
| 268 | <h5 class="subsubsectionHead"><span class="titlemark">1.1.2. </span> <a
|
|---|
| 269 | id="x1-50001.1.2"></a>Classification</h5>
|
|---|
| 270 | <!--l. 29--><p class="noindent" >Vorbis I is a forward-adaptive monolithic transform CODEC based on the Modified Discrete
|
|---|
| 271 | Cosine Transform. The codec is structured to allow addition of a hybrid wavelet filterbank in
|
|---|
| 272 | Vorbis II to offer better transient response and reproduction using a transform better suited to
|
|---|
| 273 | localized time events.
|
|---|
| 274 |
|
|---|
| 275 |
|
|---|
| 276 |
|
|---|
| 277 | <!--l. 36--><p class="noindent" >
|
|---|
| 278 | <h5 class="subsubsectionHead"><span class="titlemark">1.1.3. </span> <a
|
|---|
| 279 | id="x1-60001.1.3"></a>Assumptions</h5>
|
|---|
| 280 | <!--l. 38--><p class="noindent" >The Vorbis CODEC design assumes a complex, psychoacoustically-aware encoder and simple,
|
|---|
| 281 | low-complexity decoder. Vorbis decode is computationally simpler than mp3, although it does
|
|---|
| 282 | require more working memory as Vorbis has no static probability model; the vector codebooks
|
|---|
| 283 | used in the first stage of decoding from the bitstream are packed in their entirety into the Vorbis
|
|---|
| 284 | bitstream headers. In packed form, these codebooks occupy only a few kilobytes; the extent to
|
|---|
| 285 | which they are pre-decoded into a cache is the dominant factor in decoder memory
|
|---|
| 286 | usage.
|
|---|
| 287 | <!--l. 49--><p class="noindent" >Vorbis provides none of its own framing, synchronization or protection against errors; it
|
|---|
| 288 | is solely a method of accepting input audio, dividing it into individual frames and
|
|---|
| 289 | compressing these frames into raw, unformatted ’packets’. The decoder then accepts
|
|---|
| 290 | these raw packets in sequence, decodes them, synthesizes audio frames from them, and
|
|---|
| 291 | reassembles the frames into a facsimile of the original audio stream. Vorbis is a free-form
|
|---|
| 292 | variable bit rate (VBR) codec and packets have no minimum size, maximum size, or
|
|---|
| 293 | fixed/expected size. Packets are designed that they may be truncated (or padded)
|
|---|
| 294 | and remain decodable; this is not to be considered an error condition and is used
|
|---|
| 295 | extensively in bitrate management in peeling. Both the transport mechanism and
|
|---|
| 296 | decoder must allow that a packet may be any size, or end before or after packet decode
|
|---|
| 297 | expects.
|
|---|
| 298 | <!--l. 63--><p class="noindent" >Vorbis packets are thus intended to be used with a transport mechanism that provides free-form
|
|---|
| 299 | framing, sync, positioning and error correction in accordance with these design assumptions, such
|
|---|
| 300 | as Ogg (for file transport) or RTP (for network multicast). For purposes of a few examples in this
|
|---|
| 301 | document, we will assume that Vorbis is to be embedded in an Ogg stream specifically,
|
|---|
| 302 | although this is by no means a requirement or fundamental assumption in the Vorbis
|
|---|
| 303 | design.
|
|---|
| 304 | <!--l. 71--><p class="noindent" >The specification for embedding Vorbis into an Ogg transport stream is in <a
|
|---|
| 305 | href="#x1-128000A">section A</a>,
|
|---|
| 306 | “<a
|
|---|
| 307 | href="#x1-128000A">Embedding Vorbis into an Ogg stream<!--tex4ht:ref: vorbis:over:ogg --></a>”.
|
|---|
| 308 | <!--l. 76--><p class="noindent" >
|
|---|
| 309 | <h5 class="subsubsectionHead"><span class="titlemark">1.1.4. </span> <a
|
|---|
| 310 | id="x1-70001.1.4"></a>Codec Setup and Probability Model</h5>
|
|---|
| 311 | <!--l. 78--><p class="noindent" >Vorbis’ heritage is as a research CODEC and its current design reflects a desire to allow multiple
|
|---|
| 312 | decades of continuous encoder improvement before running out of room within the codec
|
|---|
| 313 | specification. For these reasons, configurable aspects of codec setup intentionally lean toward the
|
|---|
| 314 | extreme of forward adaptive.
|
|---|
| 315 |
|
|---|
| 316 |
|
|---|
| 317 |
|
|---|
| 318 | <!--l. 84--><p class="noindent" >The single most controversial design decision in Vorbis (and the most unusual for a Vorbis
|
|---|
| 319 | developer to keep in mind) is that the entire probability model of the codec, the Huffman and
|
|---|
| 320 | VQ codebooks, is packed into the bitstream header along with extensive CODEC setup
|
|---|
| 321 | parameters (often several hundred fields). This makes it impossible, as it would be with
|
|---|
| 322 | MPEG audio layers, to embed a simple frame type flag in each audio packet, or begin
|
|---|
| 323 | decode at any frame in the stream without having previously fetched the codec setup
|
|---|
| 324 | header.
|
|---|
| 325 | <!--l. 94--><p class="noindent" ><span class="likesubparagraphHead"><a
|
|---|
| 326 | id="x1-80001.1.4"></a><span
|
|---|
| 327 | class="cmbx-12">Note:</span></span> Vorbis <span
|
|---|
| 328 | class="cmti-12">can </span>initiate decode at any arbitrary packet within a bitstream so long as the codec
|
|---|
| 329 | has been initialized/setup with the setup headers.
|
|---|
| 330 | <!--l. 100--><p class="noindent" >Thus, Vorbis headers are both required for decode to begin and relatively large as bitstream
|
|---|
| 331 | headers go. The header size is unbounded, although for streaming a rule-of-thumb of 4kB or less
|
|---|
| 332 | is recommended (and Xiph.Org’s Vorbis encoder follows this suggestion).
|
|---|
| 333 | <!--l. 105--><p class="noindent" >Our own design work indicates the primary liability of the required header is in mindshare; it is
|
|---|
| 334 | an unusual design and thus causes some amount of complaint among engineers as this runs
|
|---|
| 335 | against current design trends (and also points out limitations in some existing software/interface
|
|---|
| 336 | designs, such as Windows’ ACM codec framework). However, we find that it does not
|
|---|
| 337 | fundamentally limit Vorbis’ suitable application space.
|
|---|
| 338 | <!--l. 114--><p class="noindent" >
|
|---|
| 339 | <h5 class="subsubsectionHead"><span class="titlemark">1.1.5. </span> <a
|
|---|
| 340 | id="x1-90001.1.5"></a>Format Specification</h5>
|
|---|
| 341 | <!--l. 115--><p class="noindent" >The Vorbis format is well-defined by its decode specification; any encoder that produces packets
|
|---|
| 342 | that are correctly decoded by the reference Vorbis decoder described below may be considered
|
|---|
| 343 | a proper Vorbis encoder. A decoder must faithfully and completely implement the
|
|---|
| 344 | specification defined below (except where noted) to be considered a proper Vorbis
|
|---|
| 345 | decoder.
|
|---|
| 346 | <!--l. 122--><p class="noindent" >
|
|---|
| 347 | <h5 class="subsubsectionHead"><span class="titlemark">1.1.6. </span> <a
|
|---|
| 348 | id="x1-100001.1.6"></a>Hardware Profile</h5>
|
|---|
| 349 |
|
|---|
| 350 |
|
|---|
| 351 |
|
|---|
| 352 | <!--l. 123--><p class="noindent" >Although Vorbis decode is computationally simple, it may still run into specific limitations of an
|
|---|
| 353 | embedded design. For this reason, embedded designs are allowed to deviate in limited ways from
|
|---|
| 354 | the ‘full’ decode specification yet still be certified compliant. These optional omissions are
|
|---|
| 355 | labelled in the spec where relevant.
|
|---|
| 356 | <!--l. 130--><p class="noindent" >
|
|---|
| 357 | <h4 class="subsectionHead"><span class="titlemark">1.2. </span> <a
|
|---|
| 358 | id="x1-110001.2"></a>Decoder Configuration</h4>
|
|---|
| 359 | <!--l. 132--><p class="noindent" >Decoder setup consists of configuration of multiple, self-contained component abstractions that
|
|---|
| 360 | perform specific functions in the decode pipeline. Each different component instance of a specific
|
|---|
| 361 | type is semantically interchangeable; decoder configuration consists both of internal component
|
|---|
| 362 | configuration, as well as arrangement of specific instances into a decode pipeline. Componentry
|
|---|
| 363 | arrangement is roughly as follows:
|
|---|
| 364 | <div class="center"
|
|---|
| 365 | >
|
|---|
| 366 | <!--l. 140--><p class="noindent" >
|
|---|
| 367 |
|
|---|
| 368 | <!--l. 141--><p class="noindent" ><img
|
|---|
| 369 | src="components.png" alt="PIC"
|
|---|
| 370 | >
|
|---|
| 371 | <br /> <div class="caption"
|
|---|
| 372 | ><span class="id">Figure 1: </span><span
|
|---|
| 373 | class="content">decoder pipeline configuration</span></div><!--tex4ht:label?: x1-110011 -->
|
|---|
| 374 | </div>
|
|---|
| 375 | <!--l. 145--><p class="noindent" >
|
|---|
| 376 | <h5 class="subsubsectionHead"><span class="titlemark">1.2.1. </span> <a
|
|---|
| 377 | id="x1-120001.2.1"></a>Global Config</h5>
|
|---|
| 378 | <!--l. 146--><p class="noindent" >Global codec configuration consists of a few audio related fields (sample rate, channels), Vorbis
|
|---|
| 379 | version (always ’0’ in Vorbis I), bitrate hints, and the lists of component instances. All other
|
|---|
| 380 | configuration is in the context of specific components.
|
|---|
| 381 | <!--l. 151--><p class="noindent" >
|
|---|
| 382 | <h5 class="subsubsectionHead"><span class="titlemark">1.2.2. </span> <a
|
|---|
| 383 | id="x1-130001.2.2"></a>Mode</h5>
|
|---|
| 384 |
|
|---|
| 385 |
|
|---|
| 386 |
|
|---|
| 387 | <!--l. 153--><p class="noindent" >Each Vorbis frame is coded according to a master ’mode’. A bitstream may use one or many
|
|---|
| 388 | modes.
|
|---|
| 389 | <!--l. 156--><p class="noindent" >The mode mechanism is used to encode a frame according to one of multiple possible
|
|---|
| 390 | methods with the intention of choosing a method best suited to that frame. Different
|
|---|
| 391 | modes are, e.g. how frame size is changed from frame to frame. The mode number of a
|
|---|
| 392 | frame serves as a top level configuration switch for all other specific aspects of frame
|
|---|
| 393 | decode.
|
|---|
| 394 | <!--l. 163--><p class="noindent" >A ’mode’ configuration consists of a frame size setting, window type (always 0, the Vorbis
|
|---|
| 395 | window, in Vorbis I), transform type (always type 0, the MDCT, in Vorbis I) and a mapping
|
|---|
| 396 | number. The mapping number specifies which mapping configuration instance to use for low-level
|
|---|
| 397 | packet decode and synthesis.
|
|---|
| 398 | <!--l. 170--><p class="noindent" >
|
|---|
| 399 | <h5 class="subsubsectionHead"><span class="titlemark">1.2.3. </span> <a
|
|---|
| 400 | id="x1-140001.2.3"></a>Mapping</h5>
|
|---|
| 401 | <!--l. 172--><p class="noindent" >A mapping contains a channel coupling description and a list of ’submaps’ that bundle sets
|
|---|
| 402 | of channel vectors together for grouped encoding and decoding. These submaps are
|
|---|
| 403 | not references to external components; the submap list is internal and specific to a
|
|---|
| 404 | mapping.
|
|---|
| 405 | <!--l. 177--><p class="noindent" >A ’submap’ is a configuration/grouping that applies to a subset of floor and residue vectors
|
|---|
| 406 | within a mapping. The submap functions as a last layer of indirection such that specific special
|
|---|
| 407 | floor or residue settings can be applied not only to all the vectors in a given mode, but also
|
|---|
| 408 | specific vectors in a specific mode. Each submap specifies the proper floor and residue
|
|---|
| 409 | instance number to use for decoding that submap’s spectral floor and spectral residue
|
|---|
| 410 | vectors.
|
|---|
| 411 | <!--l. 185--><p class="noindent" >As an example:
|
|---|
| 412 | <!--l. 187--><p class="noindent" >Assume a Vorbis stream that contains six channels in the standard 5.1 format. The sixth
|
|---|
| 413 | channel, as is normal in 5.1, is bass only. Therefore it would be wasteful to encode a
|
|---|
| 414 | full-spectrum version of it as with the other channels. The submapping mechanism can be used
|
|---|
| 415 | to apply a full range floor and residue encoding to channels 0 through 4, and a bass-only
|
|---|
| 416 | representation to the bass channel, thus saving space. In this example, channels 0-4 belong to
|
|---|
| 417 | submap 0 (which indicates use of a full-range floor) and channel 5 belongs to submap 1, which
|
|---|
| 418 | uses a bass-only representation.
|
|---|
| 419 |
|
|---|
| 420 |
|
|---|
| 421 |
|
|---|
| 422 | <!--l. 198--><p class="noindent" >
|
|---|
| 423 | <h5 class="subsubsectionHead"><span class="titlemark">1.2.4. </span> <a
|
|---|
| 424 | id="x1-150001.2.4"></a>Floor</h5>
|
|---|
| 425 | <!--l. 200--><p class="noindent" >Vorbis encodes a spectral ’floor’ vector for each PCM channel. This vector is a low-resolution
|
|---|
| 426 | representation of the audio spectrum for the given channel in the current frame, generally used
|
|---|
| 427 | akin to a whitening filter. It is named a ’floor’ because the Xiph.Org reference encoder has
|
|---|
| 428 | historically used it as a unit-baseline for spectral resolution.
|
|---|
| 429 | <!--l. 207--><p class="noindent" >A floor encoding may be of two types. Floor 0 uses a packed LSP representation on a dB
|
|---|
| 430 | amplitude scale and Bark frequency scale. Floor 1 represents the curve as a piecewise linear
|
|---|
| 431 | interpolated representation on a dB amplitude scale and linear frequency scale. The two floors
|
|---|
| 432 | are semantically interchangeable in encoding/decoding. However, floor type 1 provides more
|
|---|
| 433 | stable inter-frame behavior, and so is the preferred choice in all coupled-stereo and
|
|---|
| 434 | high bitrate modes. Floor 1 is also considerably less expensive to decode than floor
|
|---|
| 435 | 0.
|
|---|
| 436 | <!--l. 217--><p class="noindent" >Floor 0 is not to be considered deprecated, but it is of limited modern use. No known Vorbis
|
|---|
| 437 | encoder past Xiph.Org’s own beta 4 makes use of floor 0.
|
|---|
| 438 | <!--l. 221--><p class="noindent" >The values coded/decoded by a floor are both compactly formatted and make use of entropy
|
|---|
| 439 | coding to save space. For this reason, a floor configuration generally refers to multiple
|
|---|
| 440 | codebooks in the codebook component list. Entropy coding is thus provided as an
|
|---|
| 441 | abstraction, and each floor instance may choose from any and all available codebooks when
|
|---|
| 442 | coding/decoding.
|
|---|
| 443 | <!--l. 229--><p class="noindent" >
|
|---|
| 444 | <h5 class="subsubsectionHead"><span class="titlemark">1.2.5. </span> <a
|
|---|
| 445 | id="x1-160001.2.5"></a>Residue</h5>
|
|---|
| 446 | <!--l. 230--><p class="noindent" >The spectral residue is the fine structure of the audio spectrum once the floor curve has been
|
|---|
| 447 | subtracted out. In simplest terms, it is coded in the bitstream using cascaded (multi-pass) vector
|
|---|
| 448 | quantization according to one of three specific packing/coding algorithms numbered
|
|---|
| 449 | 0 through 2. The packing algorithm details are configured by residue instance. As
|
|---|
| 450 | with the floor components, the final VQ/entropy encoding is provided by external
|
|---|
| 451 | codebook instances and each residue instance may choose from any and all available
|
|---|
| 452 | codebooks.
|
|---|
| 453 | <!--l. 240--><p class="noindent" >
|
|---|
| 454 |
|
|---|
| 455 |
|
|---|
| 456 |
|
|---|
| 457 | <h5 class="subsubsectionHead"><span class="titlemark">1.2.6. </span> <a
|
|---|
| 458 | id="x1-170001.2.6"></a>Codebooks</h5>
|
|---|
| 459 | <!--l. 242--><p class="noindent" >Codebooks are a self-contained abstraction that perform entropy decoding and, optionally, use
|
|---|
| 460 | the entropy-decoded integer value as an offset into an index of output value vectors, returning
|
|---|
| 461 | the indicated vector of values.
|
|---|
| 462 | <!--l. 247--><p class="noindent" >The entropy coding in a Vorbis I codebook is provided by a standard Huffman binary tree
|
|---|
| 463 | representation. This tree is tightly packed using one of several methods, depending on whether
|
|---|
| 464 | codeword lengths are ordered or unordered, or the tree is sparse.
|
|---|
| 465 | <!--l. 252--><p class="noindent" >The codebook vector index is similarly packed according to index characteristic. Most commonly,
|
|---|
| 466 | the vector index is encoded as a single list of values of possible values that are then permuted
|
|---|
| 467 | into a list of n-dimensional rows (lattice VQ).
|
|---|
| 468 | <!--l. 259--><p class="noindent" >
|
|---|
| 469 | <h4 class="subsectionHead"><span class="titlemark">1.3. </span> <a
|
|---|
| 470 | id="x1-180001.3"></a>High-level Decode Process</h4>
|
|---|
| 471 | <!--l. 261--><p class="noindent" >
|
|---|
| 472 | <h5 class="subsubsectionHead"><span class="titlemark">1.3.1. </span> <a
|
|---|
| 473 | id="x1-190001.3.1"></a>Decode Setup</h5>
|
|---|
| 474 | <!--l. 263--><p class="noindent" >Before decoding can begin, a decoder must initialize using the bitstream headers matching the
|
|---|
| 475 | stream to be decoded. Vorbis uses three header packets; all are required, in-order, by
|
|---|
| 476 | this specification. Once set up, decode may begin at any audio packet belonging to
|
|---|
| 477 | the Vorbis stream. In Vorbis I, all packets after the three initial headers are audio
|
|---|
| 478 | packets.
|
|---|
| 479 | <!--l. 270--><p class="noindent" >The header packets are, in order, the identification header, the comments header, and the setup
|
|---|
| 480 | header.
|
|---|
| 481 | <!--l. 273--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 482 | id="x1-200001.3.1"></a><span
|
|---|
| 483 | class="cmbx-12">Identification Header</span></span>
|
|---|
| 484 | The identification header identifies the bitstream as Vorbis, Vorbis version, and the simple audio
|
|---|
| 485 | characteristics of the stream such as sample rate and number of channels.
|
|---|
| 486 |
|
|---|
| 487 |
|
|---|
| 488 |
|
|---|
| 489 | <!--l. 278--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 490 | id="x1-210001.3.1"></a><span
|
|---|
| 491 | class="cmbx-12">Comment Header</span></span>
|
|---|
| 492 | The comment header includes user text comments (“tags”) and a vendor string for the
|
|---|
| 493 | application/library that produced the bitstream. The encoding and proper use of the comment
|
|---|
| 494 | header is described in <a
|
|---|
| 495 | href="#x1-820005">section 5</a>, “<a
|
|---|
| 496 | href="#x1-820005">comment field and header specification<!--tex4ht:ref: vorbis:spec:comment --></a>”.
|
|---|
| 497 | <!--l. 283--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 498 | id="x1-220001.3.1"></a><span
|
|---|
| 499 | class="cmbx-12">Setup Header</span></span>
|
|---|
| 500 | The setup header includes extensive CODEC setup information as well as the complete VQ and
|
|---|
| 501 | Huffman codebooks needed for decode.
|
|---|
| 502 | <!--l. 288--><p class="noindent" >
|
|---|
| 503 | <h5 class="subsubsectionHead"><span class="titlemark">1.3.2. </span> <a
|
|---|
| 504 | id="x1-230001.3.2"></a>Decode Procedure</h5>
|
|---|
| 505 | <!--l. 290--><p class="noindent" >The decoding and synthesis procedure for all audio packets is fundamentally the same.
|
|---|
| 506 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 507 | 1. </dt><dd
|
|---|
| 508 | class="enumerate-enumitem">decode packet type flag
|
|---|
| 509 | </dd><dt class="enumerate-enumitem">
|
|---|
| 510 | 2. </dt><dd
|
|---|
| 511 | class="enumerate-enumitem">decode mode number
|
|---|
| 512 | </dd><dt class="enumerate-enumitem">
|
|---|
| 513 | 3. </dt><dd
|
|---|
| 514 | class="enumerate-enumitem">decode window shape (long windows only)
|
|---|
| 515 | </dd><dt class="enumerate-enumitem">
|
|---|
| 516 | 4. </dt><dd
|
|---|
| 517 | class="enumerate-enumitem">decode floor
|
|---|
| 518 | </dd><dt class="enumerate-enumitem">
|
|---|
| 519 | 5. </dt><dd
|
|---|
| 520 | class="enumerate-enumitem">decode residue into residue vectors
|
|---|
| 521 | </dd><dt class="enumerate-enumitem">
|
|---|
| 522 | 6. </dt><dd
|
|---|
| 523 | class="enumerate-enumitem">inverse channel coupling of residue vectors
|
|---|
| 524 | </dd><dt class="enumerate-enumitem">
|
|---|
| 525 | 7. </dt><dd
|
|---|
| 526 | class="enumerate-enumitem">generate floor curve from decoded floor data
|
|---|
| 527 | </dd><dt class="enumerate-enumitem">
|
|---|
| 528 | 8. </dt><dd
|
|---|
| 529 | class="enumerate-enumitem">compute dot product of floor and residue, producing audio spectrum vector
|
|---|
| 530 | </dd><dt class="enumerate-enumitem">
|
|---|
| 531 | 9. </dt><dd
|
|---|
| 532 | class="enumerate-enumitem">inverse monolithic transform of audio spectrum vector, always an MDCT in Vorbis
|
|---|
| 533 | I
|
|---|
| 534 |
|
|---|
| 535 |
|
|---|
| 536 |
|
|---|
| 537 | </dd><dt class="enumerate-enumitem">
|
|---|
| 538 | 10. </dt><dd
|
|---|
| 539 | class="enumerate-enumitem">overlap/add left-hand output of transform with right-hand output of previous frame
|
|---|
| 540 | </dd><dt class="enumerate-enumitem">
|
|---|
| 541 | 11. </dt><dd
|
|---|
| 542 | class="enumerate-enumitem">store right hand-data from transform of current frame for future lapping
|
|---|
| 543 | </dd><dt class="enumerate-enumitem">
|
|---|
| 544 | 12. </dt><dd
|
|---|
| 545 | class="enumerate-enumitem">if not first frame, return results of overlap/add as audio result of current frame</dd></dl>
|
|---|
| 546 | <!--l. 307--><p class="noindent" >Note that clever rearrangement of the synthesis arithmetic is possible; as an example, one can
|
|---|
| 547 | take advantage of symmetries in the MDCT to store the right-hand transform data of a partial
|
|---|
| 548 | MDCT for a 50% inter-frame buffer space savings, and then complete the transform later before
|
|---|
| 549 | overlap/add with the next frame. This optimization produces entirely equivalent output and is
|
|---|
| 550 | naturally perfectly legal. The decoder must be <span
|
|---|
| 551 | class="cmti-12">entirely mathematically equivalent </span>to the
|
|---|
| 552 | specification, it need not be a literal semantic implementation.
|
|---|
| 553 | <!--l. 316--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 554 | id="x1-240001.3.2"></a><span
|
|---|
| 555 | class="cmbx-12">Packet type decode</span></span>
|
|---|
| 556 | Vorbis I uses four packet types. The first three packet types mark each of the three Vorbis
|
|---|
| 557 | headers described above. The fourth packet type marks an audio packet. All other packet types
|
|---|
| 558 | are reserved; packets marked with a reserved type should be ignored.
|
|---|
| 559 | <!--l. 323--><p class="noindent" >Following the three header packets, all packets in a Vorbis I stream are audio. The first step of
|
|---|
| 560 | audio packet decode is to read and verify the packet type; <span
|
|---|
| 561 | class="cmti-12">a non-audio packet when audio is</span>
|
|---|
| 562 | <span
|
|---|
| 563 | class="cmti-12">expected indicates stream corruption or a non-compliant stream. The decoder must ignore the</span>
|
|---|
| 564 | <span
|
|---|
| 565 | class="cmti-12">packet and not attempt decoding it to audio</span>.
|
|---|
| 566 | <!--l. 333--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 567 | id="x1-250001.3.2"></a><span
|
|---|
| 568 | class="cmbx-12">Mode decode</span></span>
|
|---|
| 569 | Vorbis allows an encoder to set up multiple, numbered packet ’modes’, as described earlier, all of
|
|---|
| 570 | which may be used in a given Vorbis stream. The mode is encoded as an integer used as a direct
|
|---|
| 571 | offset into the mode instance index.
|
|---|
| 572 | <!--l. 340--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 573 | id="x1-260001.3.2"></a><span
|
|---|
| 574 | class="cmbx-12">Window shape decode (long windows only)</span></span>
|
|---|
| 575 | Vorbis frames may be one of two PCM sample sizes specified during codec setup. In Vorbis I,
|
|---|
| 576 | legal frame sizes are powers of two from 64 to 8192 samples. Aside from coupling, Vorbis
|
|---|
| 577 | handles channels as independent vectors and these frame sizes are in samples per
|
|---|
| 578 | channel.
|
|---|
| 579 |
|
|---|
| 580 |
|
|---|
| 581 |
|
|---|
| 582 | <!--l. 347--><p class="noindent" >Vorbis uses an overlapping transform, namely the MDCT, to blend one frame into the next,
|
|---|
| 583 | avoiding most inter-frame block boundary artifacts. The MDCT output of one frame is windowed
|
|---|
| 584 | according to MDCT requirements, overlapped 50% with the output of the previous frame and
|
|---|
| 585 | added. The window shape assures seamless reconstruction.
|
|---|
| 586 | <!--l. 353--><p class="noindent" >This is easy to visualize in the case of equal sized-windows:
|
|---|
| 587 | <div class="center"
|
|---|
| 588 | >
|
|---|
| 589 | <!--l. 355--><p class="noindent" >
|
|---|
| 590 |
|
|---|
| 591 | <!--l. 356--><p class="noindent" ><img
|
|---|
| 592 | src="window1.png" alt="PIC"
|
|---|
| 593 | >
|
|---|
| 594 | <br /> <div class="caption"
|
|---|
| 595 | ><span class="id">Figure 2: </span><span
|
|---|
| 596 | class="content">overlap of two equal-sized windows</span></div><!--tex4ht:label?: x1-260012 -->
|
|---|
| 597 | </div>
|
|---|
| 598 | <!--l. 360--><p class="noindent" >And slightly more complex in the case of overlapping unequal sized windows:
|
|---|
| 599 | <div class="center"
|
|---|
| 600 | >
|
|---|
| 601 | <!--l. 363--><p class="noindent" >
|
|---|
| 602 |
|
|---|
| 603 | <!--l. 364--><p class="noindent" ><img
|
|---|
| 604 | src="window2.png" alt="PIC"
|
|---|
| 605 | >
|
|---|
| 606 | <br /> <div class="caption"
|
|---|
| 607 | ><span class="id">Figure 3: </span><span
|
|---|
| 608 | class="content">overlap of a long and a short window</span></div><!--tex4ht:label?: x1-260023 -->
|
|---|
| 609 | </div>
|
|---|
| 610 | <!--l. 368--><p class="noindent" >In the unequal-sized window case, the window shape of the long window must be modified for
|
|---|
| 611 | seamless lapping as above. It is possible to correctly infer window shape to be applied to the
|
|---|
| 612 | current window from knowing the sizes of the current, previous and next window. It is legal for a
|
|---|
| 613 | decoder to use this method. However, in the case of a long window (short windows require no
|
|---|
| 614 | modification), Vorbis also codes two flag bits to specify pre- and post- window shape. Although
|
|---|
| 615 | not strictly necessary for function, this minor redundancy allows a packet to be fully decoded to
|
|---|
| 616 | the point of lapping entirely independently of any other packet, allowing easier abstraction of
|
|---|
| 617 | decode layers as well as allowing a greater level of easy parallelism in encode and
|
|---|
| 618 | decode.
|
|---|
| 619 | <!--l. 381--><p class="noindent" >A description of valid window functions for use with an inverse MDCT can be found in <span class="cite">[<a
|
|---|
| 620 | href="#XSporer/Brandenburg/Edler">1</a>]</span>.
|
|---|
| 621 | Vorbis windows all use the slope function
|
|---|
| 622 | <center class="math-display" >
|
|---|
| 623 | <img
|
|---|
| 624 | src="Vorbis_I_spec0x.png" alt="y = sin (.5 * π sin2((x + .5)∕n * π)).
|
|---|
| 625 |
|
|---|
| 626 |
|
|---|
| 627 |
|
|---|
| 628 | " class="math-display" ></center>
|
|---|
| 629 | <!--l. 384--><p class="nopar" >
|
|---|
| 630 | <!--l. 388--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 631 | id="x1-270001.3.2"></a><span
|
|---|
| 632 | class="cmbx-12">floor decode</span></span>
|
|---|
| 633 | Each floor is encoded/decoded in channel order, however each floor belongs to a ’submap’ that
|
|---|
| 634 | specifies which floor configuration to use. All floors are decoded before residue decode
|
|---|
| 635 | begins.
|
|---|
| 636 | <!--l. 394--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 637 | id="x1-280001.3.2"></a><span
|
|---|
| 638 | class="cmbx-12">residue decode</span></span>
|
|---|
| 639 | Although the number of residue vectors equals the number of channels, channel coupling may
|
|---|
| 640 | mean that the raw residue vectors extracted during decode do not map directly to specific
|
|---|
| 641 | channels. When channel coupling is in use, some vectors will correspond to coupled magnitude or
|
|---|
| 642 | angle. The coupling relationships are described in the codec setup and may differ from frame to
|
|---|
| 643 | frame, due to different mode numbers.
|
|---|
| 644 | <!--l. 403--><p class="noindent" >Vorbis codes residue vectors in groups by submap; the coding is done in submap order from
|
|---|
| 645 | submap 0 through n-1. This differs from floors which are coded using a configuration provided by
|
|---|
| 646 | submap number, but are coded individually in channel order.
|
|---|
| 647 | <!--l. 410--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 648 | id="x1-290001.3.2"></a><span
|
|---|
| 649 | class="cmbx-12">inverse channel coupling</span></span>
|
|---|
| 650 | A detailed discussion of stereo in the Vorbis codec can be found in the document
|
|---|
| 651 | <a
|
|---|
| 652 | href="stereo.html" >Stereo Channel Coupling in the Vorbis CODEC</a>. Vorbis is not limited to only stereo
|
|---|
| 653 | coupling, but the stereo document also gives a good overview of the generic coupling
|
|---|
| 654 | mechanism.
|
|---|
| 655 | <!--l. 418--><p class="noindent" >Vorbis coupling applies to pairs of residue vectors at a time; decoupling is done in-place a
|
|---|
| 656 | pair at a time in the order and using the vectors specified in the current mapping
|
|---|
| 657 | configuration. The decoupling operation is the same for all pairs, converting square polar
|
|---|
| 658 | representation (where one vector is magnitude and the second angle) back to Cartesian
|
|---|
| 659 | representation.
|
|---|
| 660 | <!--l. 425--><p class="noindent" >After decoupling, in order, each pair of vectors on the coupling list, the resulting residue vectors
|
|---|
| 661 | represent the fine spectral detail of each output channel.
|
|---|
| 662 |
|
|---|
| 663 |
|
|---|
| 664 |
|
|---|
| 665 | <!--l. 431--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 666 | id="x1-300001.3.2"></a><span
|
|---|
| 667 | class="cmbx-12">generate floor curve</span></span>
|
|---|
| 668 | The decoder may choose to generate the floor curve at any appropriate time. It is reasonable to
|
|---|
| 669 | generate the output curve when the floor data is decoded from the raw packet, or it
|
|---|
| 670 | can be generated after inverse coupling and applied to the spectral residue directly,
|
|---|
| 671 | combining generation and the dot product into one step and eliminating some working
|
|---|
| 672 | space.
|
|---|
| 673 | <!--l. 440--><p class="noindent" >Both floor 0 and floor 1 generate a linear-range, linear-domain output vector to be multiplied
|
|---|
| 674 | (dot product) by the linear-range, linear-domain spectral residue.
|
|---|
| 675 | <!--l. 446--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 676 | id="x1-310001.3.2"></a><span
|
|---|
| 677 | class="cmbx-12">compute floor/residue dot product</span></span>
|
|---|
| 678 | This step is straightforward; for each output channel, the decoder multiplies the floor curve and
|
|---|
| 679 | residue vectors element by element, producing the finished audio spectrum of each
|
|---|
| 680 | channel.
|
|---|
| 681 | <!--l. 454--><p class="noindent" >One point is worth mentioning about this dot product; a common mistake in a fixed point
|
|---|
| 682 | implementation might be to assume that a 32 bit fixed-point representation for floor and
|
|---|
| 683 | residue and direct multiplication of the vectors is sufficient for acceptable spectral depth
|
|---|
| 684 | in all cases because it happens to mostly work with the current Xiph.Org reference
|
|---|
| 685 | encoder.
|
|---|
| 686 | <!--l. 461--><p class="noindent" >However, floor vector values can span <span
|
|---|
| 687 | class="cmsy-10x-x-120">~</span>140dB (<span
|
|---|
| 688 | class="cmsy-10x-x-120">~</span>24 bits unsigned), and the audio spectrum
|
|---|
| 689 | vector should represent a minimum of 120dB (<span
|
|---|
| 690 | class="cmsy-10x-x-120">~</span>21 bits with sign), even when output is to a 16
|
|---|
| 691 | bit PCM device. For the residue vector to represent full scale if the floor is nailed
|
|---|
| 692 | to <span
|
|---|
| 693 | class="cmsy-10x-x-120">-</span>140dB, it must be able to span 0 to +140dB. For the residue vector to reach
|
|---|
| 694 | full scale if the floor is nailed at 0dB, it must be able to represent <span
|
|---|
| 695 | class="cmsy-10x-x-120">-</span>140dB to +0dB.
|
|---|
| 696 | Thus, in order to handle full range dynamics, a residue vector may span <span
|
|---|
| 697 | class="cmsy-10x-x-120">-</span>140dB to
|
|---|
| 698 | +140dB entirely within spec. A 280dB range is approximately 48 bits with sign; thus the
|
|---|
| 699 | residue vector must be able to represent a 48 bit range and the dot product must
|
|---|
| 700 | be able to handle an effective 48 bit times 24 bit multiplication. This range may be
|
|---|
| 701 | achieved using large (64 bit or larger) integers, or implementing a movable binary point
|
|---|
| 702 | representation.
|
|---|
| 703 | <!--l. 478--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 704 | id="x1-320001.3.2"></a><span
|
|---|
| 705 | class="cmbx-12">inverse monolithic transform (MDCT)</span></span>
|
|---|
| 706 | The audio spectrum is converted back into time domain PCM audio via an inverse Modified
|
|---|
| 707 | Discrete Cosine Transform (MDCT). A detailed description of the MDCT is available in
|
|---|
| 708 | <span class="cite">[<a
|
|---|
| 709 | href="#XSporer/Brandenburg/Edler">1</a>]</span>.
|
|---|
| 710 | <!--l. 484--><p class="noindent" >Note that the PCM produced directly from the MDCT is not yet finished audio; it must be
|
|---|
| 711 |
|
|---|
| 712 |
|
|---|
| 713 |
|
|---|
| 714 | lapped with surrounding frames using an appropriate window (such as the Vorbis window) before
|
|---|
| 715 | the MDCT can be considered orthogonal.
|
|---|
| 716 | <!--l. 491--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 717 | id="x1-330001.3.2"></a><span
|
|---|
| 718 | class="cmbx-12">overlap/add data</span></span>
|
|---|
| 719 | Windowed MDCT output is overlapped and added with the right hand data of the previous
|
|---|
| 720 | window such that the 3/4 point of the previous window is aligned with the 1/4 point of the
|
|---|
| 721 | current window (as illustrated in the window overlap diagram). At this point, the audio data
|
|---|
| 722 | between the center of the previous frame and the center of the current frame is now finished and
|
|---|
| 723 | ready to be returned.
|
|---|
| 724 | <!--l. 500--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 725 | id="x1-340001.3.2"></a><span
|
|---|
| 726 | class="cmbx-12">cache right hand data</span></span>
|
|---|
| 727 | The decoder must cache the right hand portion of the current frame to be lapped with the left
|
|---|
| 728 | hand portion of the next frame.
|
|---|
| 729 | <!--l. 506--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 730 | id="x1-350001.3.2"></a><span
|
|---|
| 731 | class="cmbx-12">return finished audio data</span></span>
|
|---|
| 732 | The overlapped portion produced from overlapping the previous and current frame data
|
|---|
| 733 | is finished data to be returned by the decoder. This data spans from the center of
|
|---|
| 734 | the previous window to the center of the current window. In the case of same-sized
|
|---|
| 735 | windows, the amount of data to return is one-half block consisting of and only of the
|
|---|
| 736 | overlapped portions. When overlapping a short and long window, much of the returned
|
|---|
| 737 | range is not actually overlap. This does not damage transform orthogonality. Pay
|
|---|
| 738 | attention however to returning the correct data range; the amount of data to be returned
|
|---|
| 739 | is:
|
|---|
| 740 | <!--l. 518--><p class="noindent" >
|
|---|
| 741 | <div class="fancyvrb" id="fancyvrb1"><a
|
|---|
| 742 | id="x1-35002r1"></a><span
|
|---|
| 743 | class="cmr-6">1</span><span
|
|---|
| 744 | class="cmtt-8">window</span><span
|
|---|
| 745 | class="cmtt-8">_blocksize(previous</span><span
|
|---|
| 746 | class="cmtt-8">_window)/4+window</span><span
|
|---|
| 747 | class="cmtt-8">_blocksize(current</span><span
|
|---|
| 748 | class="cmtt-8">_window)/4</span></div>
|
|---|
| 749 | <!--l. 522--><p class="noindent" >from the center of the previous window to the center of the current window.
|
|---|
| 750 | <!--l. 525--><p class="noindent" >Data is not returned from the first frame; it must be used to ’prime’ the decode engine. The
|
|---|
| 751 | encoder accounts for this priming when calculating PCM offsets; after the first frame, the proper
|
|---|
| 752 | PCM output offset is ’0’ (as no data has been returned yet).
|
|---|
| 753 |
|
|---|
| 754 |
|
|---|
| 755 |
|
|---|
| 756 |
|
|---|
| 757 |
|
|---|
| 758 |
|
|---|
| 759 | <h3 class="sectionHead"><span class="titlemark">2. </span> <a
|
|---|
| 760 | id="x1-360002"></a>Bitpacking Convention</h3>
|
|---|
| 761 | <!--l. 5--><p class="noindent" >
|
|---|
| 762 | <h4 class="subsectionHead"><span class="titlemark">2.1. </span> <a
|
|---|
| 763 | id="x1-370002.1"></a>Overview</h4>
|
|---|
| 764 | <!--l. 7--><p class="noindent" >The Vorbis codec uses relatively unstructured raw packets containing arbitrary-width binary
|
|---|
| 765 | integer fields. Logically, these packets are a bitstream in which bits are coded one-by-one by the
|
|---|
| 766 | encoder and then read one-by-one in the same monotonically increasing order by the decoder.
|
|---|
| 767 | Most current binary storage arrangements group bits into a native word size of eight bits
|
|---|
| 768 | (octets), sixteen bits, thirty-two bits or, less commonly other fixed word sizes. The Vorbis
|
|---|
| 769 | bitpacking convention specifies the correct mapping of the logical packet bitstream into an actual
|
|---|
| 770 | representation in fixed-width words.
|
|---|
| 771 | <!--l. 18--><p class="noindent" >
|
|---|
| 772 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.1. </span> <a
|
|---|
| 773 | id="x1-380002.1.1"></a>octets, bytes and words</h5>
|
|---|
| 774 | <!--l. 20--><p class="noindent" >In most contemporary architectures, a ’byte’ is synonymous with an ’octet’, that is, eight bits.
|
|---|
| 775 | This has not always been the case; seven, ten, eleven and sixteen bit ’bytes’ have been used.
|
|---|
| 776 | For purposes of the bitpacking convention, a byte implies the native, smallest integer
|
|---|
| 777 | storage representation offered by a platform. On modern platforms, this is generally
|
|---|
| 778 | assumed to be eight bits (not necessarily because of the processor but because of the
|
|---|
| 779 | filesystem/memory architecture. Modern filesystems invariably offer bytes as the fundamental
|
|---|
| 780 | atom of storage). A ’word’ is an integer size that is a grouped multiple of this smallest
|
|---|
| 781 | size.
|
|---|
| 782 | <!--l. 31--><p class="noindent" >The most ubiquitous architectures today consider a ’byte’ to be an octet (eight bits) and a word
|
|---|
| 783 | to be a group of two, four or eight bytes (16, 32 or 64 bits). Note however that the Vorbis
|
|---|
| 784 | bitpacking convention is still well defined for any native byte size; Vorbis uses the native
|
|---|
| 785 | bit-width of a given storage system. This document assumes that a byte is one octet for purposes
|
|---|
| 786 | of example.
|
|---|
| 787 | <!--l. 38--><p class="noindent" >
|
|---|
| 788 |
|
|---|
| 789 |
|
|---|
| 790 |
|
|---|
| 791 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.2. </span> <a
|
|---|
| 792 | id="x1-390002.1.2"></a>bit order</h5>
|
|---|
| 793 | <!--l. 40--><p class="noindent" >A byte has a well-defined ’least significant’ bit (LSb), which is the only bit set when the byte is
|
|---|
| 794 | storing the two’s complement integer value +1. A byte’s ’most significant’ bit (MSb) is at the
|
|---|
| 795 | opposite end of the byte. Bits in a byte are numbered from zero at the LSb to <span
|
|---|
| 796 | class="cmmi-12">n </span>(<span
|
|---|
| 797 | class="cmmi-12">n </span>= 7 in an
|
|---|
| 798 | octet) for the MSb.
|
|---|
| 799 | <!--l. 49--><p class="noindent" >
|
|---|
| 800 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.3. </span> <a
|
|---|
| 801 | id="x1-400002.1.3"></a>byte order</h5>
|
|---|
| 802 | <!--l. 51--><p class="noindent" >Words are native groupings of multiple bytes. Several byte orderings are possible in a word; the
|
|---|
| 803 | common ones are 3-2-1-0 (’big endian’ or ’most significant byte first’ in which the
|
|---|
| 804 | highest-valued byte comes first), 0-1-2-3 (’little endian’ or ’least significant byte first’ in
|
|---|
| 805 | which the lowest value byte comes first) and less commonly 3-1-2-0 and 0-2-1-3 (’mixed
|
|---|
| 806 | endian’).
|
|---|
| 807 | <!--l. 58--><p class="noindent" >The Vorbis bitpacking convention specifies storage and bitstream manipulation at the byte, not
|
|---|
| 808 | word, level, thus host word ordering is of a concern only during optimization when writing high
|
|---|
| 809 | performance code that operates on a word of storage at a time rather than by byte.
|
|---|
| 810 | Logically, bytes are always coded and decoded in order from byte zero through byte
|
|---|
| 811 | <span
|
|---|
| 812 | class="cmmi-12">n</span>.
|
|---|
| 813 | <!--l. 67--><p class="noindent" >
|
|---|
| 814 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.4. </span> <a
|
|---|
| 815 | id="x1-410002.1.4"></a>coding bits into byte sequences</h5>
|
|---|
| 816 | <!--l. 69--><p class="noindent" >The Vorbis codec has need to code arbitrary bit-width integers, from zero to 32 bits
|
|---|
| 817 | wide, into packets. These integer fields are not aligned to the boundaries of the byte
|
|---|
| 818 | representation; the next field is written at the bit position at which the previous field
|
|---|
| 819 | ends.
|
|---|
| 820 | <!--l. 74--><p class="noindent" >The encoder logically packs integers by writing the LSb of a binary integer to the logical
|
|---|
| 821 | bitstream first, followed by next least significant bit, etc, until the requested number of bits
|
|---|
| 822 | have been coded. When packing the bits into bytes, the encoder begins by placing
|
|---|
| 823 | the LSb of the integer to be written into the least significant unused bit position of
|
|---|
| 824 | the destination byte, followed by the next-least significant bit of the source integer
|
|---|
| 825 | and so on up to the requested number of bits. When all bits of the destination byte
|
|---|
| 826 | have been filled, encoding continues by zeroing all bits of the next byte and writing
|
|---|
| 827 | the next bit into the bit position 0 of that byte. Decoding follows the same process
|
|---|
| 828 |
|
|---|
| 829 |
|
|---|
| 830 |
|
|---|
| 831 | as encoding, but by reading bits from the byte stream and reassembling them into
|
|---|
| 832 | integers.
|
|---|
| 833 | <!--l. 89--><p class="noindent" >
|
|---|
| 834 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.5. </span> <a
|
|---|
| 835 | id="x1-420002.1.5"></a>signedness</h5>
|
|---|
| 836 | <!--l. 91--><p class="noindent" >The signedness of a specific number resulting from decode is to be interpreted by the decoder
|
|---|
| 837 | given decode context. That is, the three bit binary pattern ’b111’ can be taken to represent
|
|---|
| 838 | either ’seven’ as an unsigned integer, or ’-1’ as a signed, two’s complement integer. The
|
|---|
| 839 | encoder and decoder are responsible for knowing if fields are to be treated as signed or
|
|---|
| 840 | unsigned.
|
|---|
| 841 | <!--l. 100--><p class="noindent" >
|
|---|
| 842 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.6. </span> <a
|
|---|
| 843 | id="x1-430002.1.6"></a>coding example</h5>
|
|---|
| 844 | <!--l. 102--><p class="noindent" >Code the 4 bit integer value ’12’ [b1100] into an empty bytestream. Bytestream result:
|
|---|
| 845 | <!--l. 105--><p class="noindent" >
|
|---|
| 846 | <div class="fancyvrb" id="fancyvrb2"><a
|
|---|
| 847 | id="x1-43002r1"></a><span
|
|---|
| 848 | class="cmr-6">1</span><span
|
|---|
| 849 | class="cmtt-8"> </span><span
|
|---|
| 850 | class="cmtt-8"> </span><span
|
|---|
| 851 | class="cmtt-8"> </span><span
|
|---|
| 852 | class="cmtt-8"> </span><span
|
|---|
| 853 | class="cmtt-8"> </span><span
|
|---|
| 854 | class="cmtt-8"> </span><span
|
|---|
| 855 | class="cmtt-8"> </span><span
|
|---|
| 856 | class="cmtt-8"> </span><span
|
|---|
| 857 | class="cmtt-8"> </span><span
|
|---|
| 858 | class="cmtt-8"> </span><span
|
|---|
| 859 | class="cmtt-8"> </span><span
|
|---|
| 860 | class="cmtt-8"> </span><span
|
|---|
| 861 | class="cmtt-8"> </span><span
|
|---|
| 862 | class="cmtt-8"> |</span><br class="fancyvrb" /><a
|
|---|
| 863 | id="x1-43004r2"></a><span
|
|---|
| 864 | class="cmr-6">2</span><span
|
|---|
| 865 | class="cmtt-8"> </span><span
|
|---|
| 866 | class="cmtt-8"> </span><span
|
|---|
| 867 | class="cmtt-8"> </span><span
|
|---|
| 868 | class="cmtt-8"> </span><span
|
|---|
| 869 | class="cmtt-8"> </span><span
|
|---|
| 870 | class="cmtt-8"> </span><span
|
|---|
| 871 | class="cmtt-8"> </span><span
|
|---|
| 872 | class="cmtt-8"> </span><span
|
|---|
| 873 | class="cmtt-8"> </span><span
|
|---|
| 874 | class="cmtt-8"> </span><span
|
|---|
| 875 | class="cmtt-8"> </span><span
|
|---|
| 876 | class="cmtt-8"> </span><span
|
|---|
| 877 | class="cmtt-8"> </span><span
|
|---|
| 878 | class="cmtt-8"> V</span><br class="fancyvrb" /><a
|
|---|
| 879 | id="x1-43006r3"></a><span
|
|---|
| 880 | class="cmr-6">3</span><br class="fancyvrb" /><a
|
|---|
| 881 | id="x1-43008r4"></a><span
|
|---|
| 882 | class="cmr-6">4</span><span
|
|---|
| 883 | class="cmtt-8"> </span><span
|
|---|
| 884 | class="cmtt-8"> </span><span
|
|---|
| 885 | class="cmtt-8"> </span><span
|
|---|
| 886 | class="cmtt-8"> </span><span
|
|---|
| 887 | class="cmtt-8"> </span><span
|
|---|
| 888 | class="cmtt-8"> </span><span
|
|---|
| 889 | class="cmtt-8"> </span><span
|
|---|
| 890 | class="cmtt-8"> 7</span><span
|
|---|
| 891 | class="cmtt-8"> 6</span><span
|
|---|
| 892 | class="cmtt-8"> 5</span><span
|
|---|
| 893 | class="cmtt-8"> 4</span><span
|
|---|
| 894 | class="cmtt-8"> 3</span><span
|
|---|
| 895 | class="cmtt-8"> 2</span><span
|
|---|
| 896 | class="cmtt-8"> 1</span><span
|
|---|
| 897 | class="cmtt-8"> 0</span><br class="fancyvrb" /><a
|
|---|
| 898 | id="x1-43010r5"></a><span
|
|---|
| 899 | class="cmr-6">5</span><span
|
|---|
| 900 | class="cmtt-8">byte</span><span
|
|---|
| 901 | class="cmtt-8"> 0</span><span
|
|---|
| 902 | class="cmtt-8"> [0</span><span
|
|---|
| 903 | class="cmtt-8"> 0</span><span
|
|---|
| 904 | class="cmtt-8"> 0</span><span
|
|---|
| 905 | class="cmtt-8"> 0</span><span
|
|---|
| 906 | class="cmtt-8"> 1</span><span
|
|---|
| 907 | class="cmtt-8"> 1</span><span
|
|---|
| 908 | class="cmtt-8"> 0</span><span
|
|---|
| 909 | class="cmtt-8"> 0]</span><span
|
|---|
| 910 | class="cmtt-8"> </span><span
|
|---|
| 911 | class="cmtt-8"> <-</span><br class="fancyvrb" /><a
|
|---|
| 912 | id="x1-43012r6"></a><span
|
|---|
| 913 | class="cmr-6">6</span><span
|
|---|
| 914 | class="cmtt-8">byte</span><span
|
|---|
| 915 | class="cmtt-8"> 1</span><span
|
|---|
| 916 | class="cmtt-8"> [</span><span
|
|---|
| 917 | class="cmtt-8"> </span><span
|
|---|
| 918 | class="cmtt-8"> </span><span
|
|---|
| 919 | class="cmtt-8"> </span><span
|
|---|
| 920 | class="cmtt-8"> </span><span
|
|---|
| 921 | class="cmtt-8"> </span><span
|
|---|
| 922 | class="cmtt-8"> </span><span
|
|---|
| 923 | class="cmtt-8"> </span><span
|
|---|
| 924 | class="cmtt-8"> </span><span
|
|---|
| 925 | class="cmtt-8"> </span><span
|
|---|
| 926 | class="cmtt-8"> </span><span
|
|---|
| 927 | class="cmtt-8"> </span><span
|
|---|
| 928 | class="cmtt-8"> </span><span
|
|---|
| 929 | class="cmtt-8"> </span><span
|
|---|
| 930 | class="cmtt-8"> </span><span
|
|---|
| 931 | class="cmtt-8"> ]</span>
|
|---|
| 932 | <br class="fancyvrb" /><a
|
|---|
| 933 | id="x1-43014r7"></a><span
|
|---|
| 934 | class="cmr-6">7</span><span
|
|---|
| 935 | class="cmtt-8">byte</span><span
|
|---|
| 936 | class="cmtt-8"> 2</span><span
|
|---|
| 937 | class="cmtt-8"> [</span><span
|
|---|
| 938 | class="cmtt-8"> </span><span
|
|---|
| 939 | class="cmtt-8"> </span><span
|
|---|
| 940 | class="cmtt-8"> </span><span
|
|---|
| 941 | class="cmtt-8"> </span><span
|
|---|
| 942 | class="cmtt-8"> </span><span
|
|---|
| 943 | class="cmtt-8"> </span><span
|
|---|
| 944 | class="cmtt-8"> </span><span
|
|---|
| 945 | class="cmtt-8"> </span><span
|
|---|
| 946 | class="cmtt-8"> </span><span
|
|---|
| 947 | class="cmtt-8"> </span><span
|
|---|
| 948 | class="cmtt-8"> </span><span
|
|---|
| 949 | class="cmtt-8"> </span><span
|
|---|
| 950 | class="cmtt-8"> </span><span
|
|---|
| 951 | class="cmtt-8"> </span><span
|
|---|
| 952 | class="cmtt-8"> ]</span><br class="fancyvrb" /><a
|
|---|
| 953 | id="x1-43016r8"></a><span
|
|---|
| 954 | class="cmr-6">8</span><span
|
|---|
| 955 | class="cmtt-8">byte</span><span
|
|---|
| 956 | class="cmtt-8"> 3</span><span
|
|---|
| 957 | class="cmtt-8"> [</span><span
|
|---|
| 958 | class="cmtt-8"> </span><span
|
|---|
| 959 | class="cmtt-8"> </span><span
|
|---|
| 960 | class="cmtt-8"> </span><span
|
|---|
| 961 | class="cmtt-8"> </span><span
|
|---|
| 962 | class="cmtt-8"> </span><span
|
|---|
| 963 | class="cmtt-8"> </span><span
|
|---|
| 964 | class="cmtt-8"> </span><span
|
|---|
| 965 | class="cmtt-8"> </span><span
|
|---|
| 966 | class="cmtt-8"> </span><span
|
|---|
| 967 | class="cmtt-8"> </span><span
|
|---|
| 968 | class="cmtt-8"> </span><span
|
|---|
| 969 | class="cmtt-8"> </span><span
|
|---|
| 970 | class="cmtt-8"> </span><span
|
|---|
| 971 | class="cmtt-8"> </span><span
|
|---|
| 972 | class="cmtt-8"> ]</span><br class="fancyvrb" /><a
|
|---|
| 973 | id="x1-43018r9"></a><span
|
|---|
| 974 | class="cmr-6">9</span><span
|
|---|
| 975 | class="cmtt-8"> </span><span
|
|---|
| 976 | class="cmtt-8"> </span><span
|
|---|
| 977 | class="cmtt-8"> </span><span
|
|---|
| 978 | class="cmtt-8"> </span><span
|
|---|
| 979 | class="cmtt-8"> </span><span
|
|---|
| 980 | class="cmtt-8"> </span><span
|
|---|
| 981 | class="cmtt-8"> </span><span
|
|---|
| 982 | class="cmtt-8"> </span><span
|
|---|
| 983 | class="cmtt-8"> </span><span
|
|---|
| 984 | class="cmtt-8"> </span><span
|
|---|
| 985 | class="cmtt-8"> </span><span
|
|---|
| 986 | class="cmtt-8"> </span><span
|
|---|
| 987 | class="cmtt-8"> ...</span><br class="fancyvrb" /><a
|
|---|
| 988 | id="x1-43020r10"></a><span
|
|---|
| 989 | class="cmr-6">10</span><span
|
|---|
| 990 | class="cmtt-8">byte</span><span
|
|---|
| 991 | class="cmtt-8"> n</span><span
|
|---|
| 992 | class="cmtt-8"> [</span><span
|
|---|
| 993 | class="cmtt-8"> </span><span
|
|---|
| 994 | class="cmtt-8"> </span><span
|
|---|
| 995 | class="cmtt-8"> </span><span
|
|---|
| 996 | class="cmtt-8"> </span><span
|
|---|
| 997 | class="cmtt-8"> </span><span
|
|---|
| 998 | class="cmtt-8"> </span><span
|
|---|
| 999 | class="cmtt-8"> </span><span
|
|---|
| 1000 | class="cmtt-8"> </span><span
|
|---|
| 1001 | class="cmtt-8"> </span><span
|
|---|
| 1002 | class="cmtt-8"> </span><span
|
|---|
| 1003 | class="cmtt-8"> </span><span
|
|---|
| 1004 | class="cmtt-8"> </span><span
|
|---|
| 1005 | class="cmtt-8"> </span><span
|
|---|
| 1006 | class="cmtt-8"> </span><span
|
|---|
| 1007 | class="cmtt-8"> ]</span><span
|
|---|
| 1008 | class="cmtt-8"> </span><span
|
|---|
| 1009 | class="cmtt-8"> bytestream</span><span
|
|---|
| 1010 | class="cmtt-8"> length</span><span
|
|---|
| 1011 | class="cmtt-8"> ==</span><span
|
|---|
| 1012 | class="cmtt-8"> 1</span><span
|
|---|
| 1013 | class="cmtt-8"> byte</span><br class="fancyvrb" /><a
|
|---|
| 1014 | id="x1-43022r11"></a><span
|
|---|
| 1015 | class="cmr-6">11</span></div>
|
|---|
| 1016 | <!--l. 120--><p class="noindent" >Continue by coding the 3 bit integer value ’-1’ [b111]:
|
|---|
| 1017 | <!--l. 122--><p class="noindent" >
|
|---|
| 1018 | <div class="fancyvrb" id="fancyvrb3"><a
|
|---|
| 1019 | id="x1-43024r1"></a><span
|
|---|
| 1020 | class="cmr-6">1</span><span
|
|---|
| 1021 | class="cmtt-8"> </span><span
|
|---|
| 1022 | class="cmtt-8"> </span><span
|
|---|
| 1023 | class="cmtt-8"> </span><span
|
|---|
| 1024 | class="cmtt-8"> </span><span
|
|---|
| 1025 | class="cmtt-8"> </span><span
|
|---|
| 1026 | class="cmtt-8"> </span><span
|
|---|
| 1027 | class="cmtt-8"> </span><span
|
|---|
| 1028 | class="cmtt-8"> |</span><br class="fancyvrb" /><a
|
|---|
| 1029 | id="x1-43026r2"></a><span
|
|---|
| 1030 | class="cmr-6">2</span><span
|
|---|
| 1031 | class="cmtt-8"> </span><span
|
|---|
| 1032 | class="cmtt-8"> </span><span
|
|---|
| 1033 | class="cmtt-8"> </span><span
|
|---|
| 1034 | class="cmtt-8"> </span><span
|
|---|
| 1035 | class="cmtt-8"> </span><span
|
|---|
| 1036 | class="cmtt-8"> </span><span
|
|---|
| 1037 | class="cmtt-8"> </span><span
|
|---|
| 1038 | class="cmtt-8"> V</span><br class="fancyvrb" /><a
|
|---|
| 1039 | id="x1-43028r3"></a><span
|
|---|
| 1040 | class="cmr-6">3</span><br class="fancyvrb" /><a
|
|---|
| 1041 | id="x1-43030r4"></a><span
|
|---|
| 1042 | class="cmr-6">4</span><span
|
|---|
| 1043 | class="cmtt-8"> </span><span
|
|---|
| 1044 | class="cmtt-8"> </span><span
|
|---|
| 1045 | class="cmtt-8"> </span><span
|
|---|
| 1046 | class="cmtt-8"> </span><span
|
|---|
| 1047 | class="cmtt-8"> </span><span
|
|---|
| 1048 | class="cmtt-8"> </span><span
|
|---|
| 1049 | class="cmtt-8"> </span><span
|
|---|
| 1050 | class="cmtt-8"> 7</span><span
|
|---|
| 1051 | class="cmtt-8"> 6</span><span
|
|---|
| 1052 | class="cmtt-8"> 5</span><span
|
|---|
| 1053 | class="cmtt-8"> 4</span><span
|
|---|
| 1054 | class="cmtt-8"> 3</span><span
|
|---|
| 1055 | class="cmtt-8"> 2</span><span
|
|---|
| 1056 | class="cmtt-8"> 1</span><span
|
|---|
| 1057 | class="cmtt-8"> 0</span><br class="fancyvrb" /><a
|
|---|
| 1058 | id="x1-43032r5"></a><span
|
|---|
| 1059 | class="cmr-6">5</span><span
|
|---|
| 1060 | class="cmtt-8">byte</span><span
|
|---|
| 1061 | class="cmtt-8"> 0</span><span
|
|---|
| 1062 | class="cmtt-8"> [0</span><span
|
|---|
| 1063 | class="cmtt-8"> 1</span><span
|
|---|
| 1064 | class="cmtt-8"> 1</span><span
|
|---|
| 1065 | class="cmtt-8"> 1</span><span
|
|---|
| 1066 | class="cmtt-8"> 1</span><span
|
|---|
| 1067 | class="cmtt-8"> 1</span><span
|
|---|
| 1068 | class="cmtt-8"> 0</span><span
|
|---|
| 1069 | class="cmtt-8"> 0]</span><span
|
|---|
| 1070 | class="cmtt-8"> </span><span
|
|---|
| 1071 | class="cmtt-8"> <-</span><br class="fancyvrb" /><a
|
|---|
| 1072 | id="x1-43034r6"></a><span
|
|---|
| 1073 | class="cmr-6">6</span><span
|
|---|
| 1074 | class="cmtt-8">byte</span><span
|
|---|
| 1075 | class="cmtt-8"> 1</span><span
|
|---|
| 1076 | class="cmtt-8"> [</span><span
|
|---|
| 1077 | class="cmtt-8"> </span><span
|
|---|
| 1078 | class="cmtt-8"> </span><span
|
|---|
| 1079 | class="cmtt-8"> </span><span
|
|---|
| 1080 | class="cmtt-8"> </span><span
|
|---|
| 1081 | class="cmtt-8"> </span><span
|
|---|
| 1082 | class="cmtt-8"> </span><span
|
|---|
| 1083 | class="cmtt-8"> </span><span
|
|---|
| 1084 | class="cmtt-8"> </span><span
|
|---|
| 1085 | class="cmtt-8"> </span><span
|
|---|
| 1086 | class="cmtt-8"> </span><span
|
|---|
| 1087 | class="cmtt-8"> </span><span
|
|---|
| 1088 | class="cmtt-8"> </span><span
|
|---|
| 1089 | class="cmtt-8"> </span><span
|
|---|
| 1090 | class="cmtt-8"> </span><span
|
|---|
| 1091 | class="cmtt-8"> ]</span><br class="fancyvrb" /><a
|
|---|
| 1092 | id="x1-43036r7"></a><span
|
|---|
| 1093 | class="cmr-6">7</span><span
|
|---|
| 1094 | class="cmtt-8">byte</span><span
|
|---|
| 1095 | class="cmtt-8"> 2</span><span
|
|---|
| 1096 | class="cmtt-8"> [</span><span
|
|---|
| 1097 | class="cmtt-8"> </span><span
|
|---|
| 1098 | class="cmtt-8"> </span><span
|
|---|
| 1099 | class="cmtt-8"> </span><span
|
|---|
| 1100 | class="cmtt-8"> </span><span
|
|---|
| 1101 | class="cmtt-8"> </span><span
|
|---|
| 1102 | class="cmtt-8"> </span><span
|
|---|
| 1103 | class="cmtt-8"> </span><span
|
|---|
| 1104 | class="cmtt-8"> </span><span
|
|---|
| 1105 | class="cmtt-8"> </span><span
|
|---|
| 1106 | class="cmtt-8"> </span><span
|
|---|
| 1107 | class="cmtt-8"> </span><span
|
|---|
| 1108 | class="cmtt-8"> </span><span
|
|---|
| 1109 | class="cmtt-8"> </span><span
|
|---|
| 1110 | class="cmtt-8"> </span><span
|
|---|
| 1111 | class="cmtt-8"> ]</span>
|
|---|
| 1112 | <br class="fancyvrb" /><a
|
|---|
| 1113 | id="x1-43038r8"></a><span
|
|---|
| 1114 | class="cmr-6">8</span><span
|
|---|
| 1115 | class="cmtt-8">byte</span><span
|
|---|
| 1116 | class="cmtt-8"> 3</span><span
|
|---|
| 1117 | class="cmtt-8"> [</span><span
|
|---|
| 1118 | class="cmtt-8"> </span><span
|
|---|
| 1119 | class="cmtt-8"> </span><span
|
|---|
| 1120 | class="cmtt-8"> </span><span
|
|---|
| 1121 | class="cmtt-8"> </span><span
|
|---|
| 1122 | class="cmtt-8"> </span><span
|
|---|
| 1123 | class="cmtt-8"> </span><span
|
|---|
| 1124 | class="cmtt-8"> </span><span
|
|---|
| 1125 | class="cmtt-8"> </span><span
|
|---|
| 1126 | class="cmtt-8"> </span><span
|
|---|
| 1127 | class="cmtt-8"> </span><span
|
|---|
| 1128 | class="cmtt-8"> </span><span
|
|---|
| 1129 | class="cmtt-8"> </span><span
|
|---|
| 1130 | class="cmtt-8"> </span><span
|
|---|
| 1131 | class="cmtt-8"> </span><span
|
|---|
| 1132 | class="cmtt-8"> ]</span><br class="fancyvrb" /><a
|
|---|
| 1133 | id="x1-43040r9"></a><span
|
|---|
| 1134 | class="cmr-6">9</span><span
|
|---|
| 1135 | class="cmtt-8"> </span><span
|
|---|
| 1136 | class="cmtt-8"> </span><span
|
|---|
| 1137 | class="cmtt-8"> </span><span
|
|---|
| 1138 | class="cmtt-8"> </span><span
|
|---|
| 1139 | class="cmtt-8"> </span><span
|
|---|
| 1140 | class="cmtt-8"> </span><span
|
|---|
| 1141 | class="cmtt-8"> </span><span
|
|---|
| 1142 | class="cmtt-8"> </span><span
|
|---|
| 1143 | class="cmtt-8"> </span><span
|
|---|
| 1144 | class="cmtt-8"> </span><span
|
|---|
| 1145 | class="cmtt-8"> </span><span
|
|---|
| 1146 | class="cmtt-8"> </span><span
|
|---|
| 1147 | class="cmtt-8"> ...</span><br class="fancyvrb" /><a
|
|---|
| 1148 | id="x1-43042r10"></a><span
|
|---|
| 1149 | class="cmr-6">10</span><span
|
|---|
| 1150 | class="cmtt-8">byte</span><span
|
|---|
| 1151 | class="cmtt-8"> n</span><span
|
|---|
| 1152 | class="cmtt-8"> [</span><span
|
|---|
| 1153 | class="cmtt-8"> </span><span
|
|---|
| 1154 | class="cmtt-8"> </span><span
|
|---|
| 1155 | class="cmtt-8"> </span><span
|
|---|
| 1156 | class="cmtt-8"> </span><span
|
|---|
| 1157 | class="cmtt-8"> </span><span
|
|---|
| 1158 | class="cmtt-8"> </span><span
|
|---|
| 1159 | class="cmtt-8"> </span><span
|
|---|
| 1160 | class="cmtt-8"> </span><span
|
|---|
| 1161 | class="cmtt-8"> </span><span
|
|---|
| 1162 | class="cmtt-8"> </span><span
|
|---|
| 1163 | class="cmtt-8"> </span><span
|
|---|
| 1164 | class="cmtt-8"> </span><span
|
|---|
| 1165 | class="cmtt-8"> </span><span
|
|---|
| 1166 | class="cmtt-8"> </span><span
|
|---|
| 1167 | class="cmtt-8"> ]</span><span
|
|---|
| 1168 | class="cmtt-8"> </span><span
|
|---|
| 1169 | class="cmtt-8"> bytestream</span><span
|
|---|
| 1170 | class="cmtt-8"> length</span><span
|
|---|
| 1171 | class="cmtt-8"> ==</span><span
|
|---|
| 1172 | class="cmtt-8"> 1</span><span
|
|---|
| 1173 | class="cmtt-8"> byte</span></div>
|
|---|
| 1174 | <!--l. 136--><p class="noindent" >Continue by coding the 7 bit integer value ’17’ [b0010001]:
|
|---|
| 1175 | <!--l. 138--><p class="noindent" >
|
|---|
| 1176 | <div class="fancyvrb" id="fancyvrb4"><a
|
|---|
| 1177 | id="x1-43044r1"></a><span
|
|---|
| 1178 | class="cmr-6">1</span><span
|
|---|
| 1179 | class="cmtt-8"> </span><span
|
|---|
| 1180 | class="cmtt-8"> </span><span
|
|---|
| 1181 | class="cmtt-8"> </span><span
|
|---|
| 1182 | class="cmtt-8"> </span><span
|
|---|
| 1183 | class="cmtt-8"> </span><span
|
|---|
| 1184 | class="cmtt-8"> </span><span
|
|---|
| 1185 | class="cmtt-8"> </span><span
|
|---|
| 1186 | class="cmtt-8"> </span><span
|
|---|
| 1187 | class="cmtt-8"> </span><span
|
|---|
| 1188 | class="cmtt-8"> |</span><br class="fancyvrb" /><a
|
|---|
| 1189 | id="x1-43046r2"></a><span
|
|---|
| 1190 | class="cmr-6">2</span><span
|
|---|
| 1191 | class="cmtt-8"> </span><span
|
|---|
| 1192 | class="cmtt-8"> </span><span
|
|---|
| 1193 | class="cmtt-8"> </span><span
|
|---|
| 1194 | class="cmtt-8"> </span><span
|
|---|
| 1195 | class="cmtt-8"> </span><span
|
|---|
| 1196 | class="cmtt-8"> </span><span
|
|---|
| 1197 | class="cmtt-8"> </span><span
|
|---|
| 1198 | class="cmtt-8"> </span><span
|
|---|
| 1199 | class="cmtt-8"> </span><span
|
|---|
| 1200 | class="cmtt-8"> V</span><br class="fancyvrb" /><a
|
|---|
| 1201 | id="x1-43048r3"></a><span
|
|---|
| 1202 | class="cmr-6">3</span><br class="fancyvrb" /><a
|
|---|
| 1203 | id="x1-43050r4"></a><span
|
|---|
| 1204 | class="cmr-6">4</span><span
|
|---|
| 1205 | class="cmtt-8"> </span><span
|
|---|
| 1206 | class="cmtt-8"> </span><span
|
|---|
| 1207 | class="cmtt-8"> </span><span
|
|---|
| 1208 | class="cmtt-8"> </span><span
|
|---|
| 1209 | class="cmtt-8"> </span><span
|
|---|
| 1210 | class="cmtt-8"> </span><span
|
|---|
| 1211 | class="cmtt-8"> </span><span
|
|---|
| 1212 | class="cmtt-8"> 7</span><span
|
|---|
| 1213 | class="cmtt-8"> 6</span><span
|
|---|
| 1214 | class="cmtt-8"> 5</span><span
|
|---|
| 1215 | class="cmtt-8"> 4</span><span
|
|---|
| 1216 | class="cmtt-8"> 3</span><span
|
|---|
| 1217 | class="cmtt-8"> 2</span><span
|
|---|
| 1218 | class="cmtt-8"> 1</span><span
|
|---|
| 1219 | class="cmtt-8"> 0</span><br class="fancyvrb" /><a
|
|---|
| 1220 | id="x1-43052r5"></a><span
|
|---|
| 1221 | class="cmr-6">5</span><span
|
|---|
| 1222 | class="cmtt-8">byte</span><span
|
|---|
| 1223 | class="cmtt-8"> 0</span><span
|
|---|
| 1224 | class="cmtt-8"> [1</span><span
|
|---|
| 1225 | class="cmtt-8"> 1</span><span
|
|---|
| 1226 | class="cmtt-8"> 1</span><span
|
|---|
| 1227 | class="cmtt-8"> 1</span><span
|
|---|
| 1228 | class="cmtt-8"> 1</span><span
|
|---|
| 1229 | class="cmtt-8"> 1</span><span
|
|---|
| 1230 | class="cmtt-8"> 0</span><span
|
|---|
| 1231 | class="cmtt-8"> 0]</span><br class="fancyvrb" /><a
|
|---|
| 1232 | id="x1-43054r6"></a><span
|
|---|
| 1233 | class="cmr-6">6</span><span
|
|---|
| 1234 | class="cmtt-8">byte</span><span
|
|---|
| 1235 | class="cmtt-8"> 1</span><span
|
|---|
| 1236 | class="cmtt-8"> [0</span><span
|
|---|
| 1237 | class="cmtt-8"> 0</span><span
|
|---|
| 1238 | class="cmtt-8"> 0</span><span
|
|---|
| 1239 | class="cmtt-8"> 0</span><span
|
|---|
| 1240 | class="cmtt-8"> 1</span><span
|
|---|
| 1241 | class="cmtt-8"> 0</span><span
|
|---|
| 1242 | class="cmtt-8"> 0</span><span
|
|---|
| 1243 | class="cmtt-8"> 0]</span><span
|
|---|
| 1244 | class="cmtt-8"> </span><span
|
|---|
| 1245 | class="cmtt-8"> <-</span><br class="fancyvrb" /><a
|
|---|
| 1246 | id="x1-43056r7"></a><span
|
|---|
| 1247 | class="cmr-6">7</span><span
|
|---|
| 1248 | class="cmtt-8">byte</span><span
|
|---|
| 1249 | class="cmtt-8"> 2</span><span
|
|---|
| 1250 | class="cmtt-8"> [</span><span
|
|---|
| 1251 | class="cmtt-8"> </span><span
|
|---|
| 1252 | class="cmtt-8"> </span><span
|
|---|
| 1253 | class="cmtt-8"> </span><span
|
|---|
| 1254 | class="cmtt-8"> </span><span
|
|---|
| 1255 | class="cmtt-8"> </span><span
|
|---|
| 1256 | class="cmtt-8"> </span><span
|
|---|
| 1257 | class="cmtt-8"> </span><span
|
|---|
| 1258 | class="cmtt-8"> </span><span
|
|---|
| 1259 | class="cmtt-8"> </span><span
|
|---|
| 1260 | class="cmtt-8"> </span><span
|
|---|
| 1261 | class="cmtt-8"> </span><span
|
|---|
| 1262 | class="cmtt-8"> </span><span
|
|---|
| 1263 | class="cmtt-8"> </span><span
|
|---|
| 1264 | class="cmtt-8"> </span><span
|
|---|
| 1265 | class="cmtt-8"> ]</span>
|
|---|
| 1266 | <br class="fancyvrb" /><a
|
|---|
| 1267 | id="x1-43058r8"></a><span
|
|---|
| 1268 | class="cmr-6">8</span><span
|
|---|
| 1269 | class="cmtt-8">byte</span><span
|
|---|
| 1270 | class="cmtt-8"> 3</span><span
|
|---|
| 1271 | class="cmtt-8"> [</span><span
|
|---|
| 1272 | class="cmtt-8"> </span><span
|
|---|
| 1273 | class="cmtt-8"> </span><span
|
|---|
| 1274 | class="cmtt-8"> </span><span
|
|---|
| 1275 | class="cmtt-8"> </span><span
|
|---|
| 1276 | class="cmtt-8"> </span><span
|
|---|
| 1277 | class="cmtt-8"> </span><span
|
|---|
| 1278 | class="cmtt-8"> </span><span
|
|---|
| 1279 | class="cmtt-8"> </span><span
|
|---|
| 1280 | class="cmtt-8"> </span><span
|
|---|
| 1281 | class="cmtt-8"> </span><span
|
|---|
| 1282 | class="cmtt-8"> </span><span
|
|---|
| 1283 | class="cmtt-8"> </span><span
|
|---|
| 1284 | class="cmtt-8"> </span><span
|
|---|
| 1285 | class="cmtt-8"> </span><span
|
|---|
| 1286 | class="cmtt-8"> ]</span><br class="fancyvrb" /><a
|
|---|
| 1287 | id="x1-43060r9"></a><span
|
|---|
| 1288 | class="cmr-6">9</span><span
|
|---|
| 1289 | class="cmtt-8"> </span><span
|
|---|
| 1290 | class="cmtt-8"> </span><span
|
|---|
| 1291 | class="cmtt-8"> </span><span
|
|---|
| 1292 | class="cmtt-8"> </span><span
|
|---|
| 1293 | class="cmtt-8"> </span><span
|
|---|
| 1294 | class="cmtt-8"> </span><span
|
|---|
| 1295 | class="cmtt-8"> </span><span
|
|---|
| 1296 | class="cmtt-8"> </span><span
|
|---|
| 1297 | class="cmtt-8"> </span><span
|
|---|
| 1298 | class="cmtt-8"> </span><span
|
|---|
| 1299 | class="cmtt-8"> </span><span
|
|---|
| 1300 | class="cmtt-8"> </span><span
|
|---|
| 1301 | class="cmtt-8"> ...</span><br class="fancyvrb" /><a
|
|---|
| 1302 | id="x1-43062r10"></a><span
|
|---|
| 1303 | class="cmr-6">10</span><span
|
|---|
| 1304 | class="cmtt-8">byte</span><span
|
|---|
| 1305 | class="cmtt-8"> n</span><span
|
|---|
| 1306 | class="cmtt-8"> [</span><span
|
|---|
| 1307 | class="cmtt-8"> </span><span
|
|---|
| 1308 | class="cmtt-8"> </span><span
|
|---|
| 1309 | class="cmtt-8"> </span><span
|
|---|
| 1310 | class="cmtt-8"> </span><span
|
|---|
| 1311 | class="cmtt-8"> </span><span
|
|---|
| 1312 | class="cmtt-8"> </span><span
|
|---|
| 1313 | class="cmtt-8"> </span><span
|
|---|
| 1314 | class="cmtt-8"> </span><span
|
|---|
| 1315 | class="cmtt-8"> </span><span
|
|---|
| 1316 | class="cmtt-8"> </span><span
|
|---|
| 1317 | class="cmtt-8"> </span><span
|
|---|
| 1318 | class="cmtt-8"> </span><span
|
|---|
| 1319 | class="cmtt-8"> </span><span
|
|---|
| 1320 | class="cmtt-8"> </span><span
|
|---|
| 1321 | class="cmtt-8"> ]</span><span
|
|---|
| 1322 | class="cmtt-8"> </span><span
|
|---|
| 1323 | class="cmtt-8"> bytestream</span><span
|
|---|
| 1324 | class="cmtt-8"> length</span><span
|
|---|
| 1325 | class="cmtt-8"> ==</span><span
|
|---|
| 1326 | class="cmtt-8"> 2</span><span
|
|---|
| 1327 | class="cmtt-8"> bytes</span><br class="fancyvrb" /><a
|
|---|
| 1328 | id="x1-43064r11"></a><span
|
|---|
| 1329 | class="cmr-6">11</span><span
|
|---|
| 1330 | class="cmtt-8"> </span><span
|
|---|
| 1331 | class="cmtt-8"> </span><span
|
|---|
| 1332 | class="cmtt-8"> </span><span
|
|---|
| 1333 | class="cmtt-8"> </span><span
|
|---|
| 1334 | class="cmtt-8"> </span><span
|
|---|
| 1335 | class="cmtt-8"> </span><span
|
|---|
| 1336 | class="cmtt-8"> </span><span
|
|---|
| 1337 | class="cmtt-8"> </span><span
|
|---|
| 1338 | class="cmtt-8"> </span><span
|
|---|
| 1339 | class="cmtt-8"> </span><span
|
|---|
| 1340 | class="cmtt-8"> </span><span
|
|---|
| 1341 | class="cmtt-8"> </span><span
|
|---|
| 1342 | class="cmtt-8"> </span><span
|
|---|
| 1343 | class="cmtt-8"> </span><span
|
|---|
| 1344 | class="cmtt-8"> </span><span
|
|---|
| 1345 | class="cmtt-8"> </span><span
|
|---|
| 1346 | class="cmtt-8"> </span><span
|
|---|
| 1347 | class="cmtt-8"> </span><span
|
|---|
| 1348 | class="cmtt-8"> </span><span
|
|---|
| 1349 | class="cmtt-8"> </span><span
|
|---|
| 1350 | class="cmtt-8"> </span><span
|
|---|
| 1351 | class="cmtt-8"> </span><span
|
|---|
| 1352 | class="cmtt-8"> </span><span
|
|---|
| 1353 | class="cmtt-8"> </span><span
|
|---|
| 1354 | class="cmtt-8"> </span><span
|
|---|
| 1355 | class="cmtt-8"> bit</span><span
|
|---|
| 1356 | class="cmtt-8"> cursor</span><span
|
|---|
| 1357 | class="cmtt-8"> ==</span><span
|
|---|
| 1358 | class="cmtt-8"> 6</span></div>
|
|---|
| 1359 | <!--l. 153--><p class="noindent" >Continue by coding the 13 bit integer value ’6969’ [b110 11001110 01]:
|
|---|
| 1360 | <!--l. 155--><p class="noindent" >
|
|---|
| 1361 | <div class="fancyvrb" id="fancyvrb5"><a
|
|---|
| 1362 | id="x1-43066r1"></a><span
|
|---|
| 1363 | class="cmr-6">1</span><span
|
|---|
| 1364 | class="cmtt-8"> </span><span
|
|---|
| 1365 | class="cmtt-8"> </span><span
|
|---|
| 1366 | class="cmtt-8"> </span><span
|
|---|
| 1367 | class="cmtt-8"> </span><span
|
|---|
| 1368 | class="cmtt-8"> </span><span
|
|---|
| 1369 | class="cmtt-8"> </span><span
|
|---|
| 1370 | class="cmtt-8"> </span><span
|
|---|
| 1371 | class="cmtt-8"> </span><span
|
|---|
| 1372 | class="cmtt-8"> </span><span
|
|---|
| 1373 | class="cmtt-8"> </span><span
|
|---|
| 1374 | class="cmtt-8"> </span><span
|
|---|
| 1375 | class="cmtt-8"> </span><span
|
|---|
| 1376 | class="cmtt-8"> </span><span
|
|---|
| 1377 | class="cmtt-8"> </span><span
|
|---|
| 1378 | class="cmtt-8"> </span><span
|
|---|
| 1379 | class="cmtt-8"> |</span><br class="fancyvrb" /><a
|
|---|
| 1380 | id="x1-43068r2"></a><span
|
|---|
| 1381 | class="cmr-6">2</span><span
|
|---|
| 1382 | class="cmtt-8"> </span><span
|
|---|
| 1383 | class="cmtt-8"> </span><span
|
|---|
| 1384 | class="cmtt-8"> </span><span
|
|---|
| 1385 | class="cmtt-8"> </span><span
|
|---|
| 1386 | class="cmtt-8"> </span><span
|
|---|
| 1387 | class="cmtt-8"> </span><span
|
|---|
| 1388 | class="cmtt-8"> </span><span
|
|---|
| 1389 | class="cmtt-8"> </span><span
|
|---|
| 1390 | class="cmtt-8"> </span><span
|
|---|
| 1391 | class="cmtt-8"> </span><span
|
|---|
| 1392 | class="cmtt-8"> </span><span
|
|---|
| 1393 | class="cmtt-8"> </span><span
|
|---|
| 1394 | class="cmtt-8"> </span><span
|
|---|
| 1395 | class="cmtt-8"> </span><span
|
|---|
| 1396 | class="cmtt-8"> </span><span
|
|---|
| 1397 | class="cmtt-8"> V</span><br class="fancyvrb" /><a
|
|---|
| 1398 | id="x1-43070r3"></a><span
|
|---|
| 1399 | class="cmr-6">3</span><br class="fancyvrb" /><a
|
|---|
| 1400 | id="x1-43072r4"></a><span
|
|---|
| 1401 | class="cmr-6">4</span><span
|
|---|
| 1402 | class="cmtt-8"> </span><span
|
|---|
| 1403 | class="cmtt-8"> </span><span
|
|---|
| 1404 | class="cmtt-8"> </span><span
|
|---|
| 1405 | class="cmtt-8"> </span><span
|
|---|
| 1406 | class="cmtt-8"> </span><span
|
|---|
| 1407 | class="cmtt-8"> </span><span
|
|---|
| 1408 | class="cmtt-8"> </span><span
|
|---|
| 1409 | class="cmtt-8"> 7</span><span
|
|---|
| 1410 | class="cmtt-8"> 6</span><span
|
|---|
| 1411 | class="cmtt-8"> 5</span><span
|
|---|
| 1412 | class="cmtt-8"> 4</span><span
|
|---|
| 1413 | class="cmtt-8"> 3</span><span
|
|---|
| 1414 | class="cmtt-8"> 2</span><span
|
|---|
| 1415 | class="cmtt-8"> 1</span><span
|
|---|
| 1416 | class="cmtt-8"> 0</span><br class="fancyvrb" /><a
|
|---|
| 1417 | id="x1-43074r5"></a><span
|
|---|
| 1418 | class="cmr-6">5</span><span
|
|---|
| 1419 | class="cmtt-8">byte</span><span
|
|---|
| 1420 | class="cmtt-8"> 0</span><span
|
|---|
| 1421 | class="cmtt-8"> [1</span><span
|
|---|
| 1422 | class="cmtt-8"> 1</span><span
|
|---|
| 1423 | class="cmtt-8"> 1</span><span
|
|---|
| 1424 | class="cmtt-8"> 1</span><span
|
|---|
| 1425 | class="cmtt-8"> 1</span><span
|
|---|
| 1426 | class="cmtt-8"> 1</span><span
|
|---|
| 1427 | class="cmtt-8"> 0</span><span
|
|---|
| 1428 | class="cmtt-8"> 0]</span><br class="fancyvrb" /><a
|
|---|
| 1429 | id="x1-43076r6"></a><span
|
|---|
| 1430 | class="cmr-6">6</span><span
|
|---|
| 1431 | class="cmtt-8">byte</span><span
|
|---|
| 1432 | class="cmtt-8"> 1</span><span
|
|---|
| 1433 | class="cmtt-8"> [0</span><span
|
|---|
| 1434 | class="cmtt-8"> 1</span><span
|
|---|
| 1435 | class="cmtt-8"> 0</span><span
|
|---|
| 1436 | class="cmtt-8"> 0</span><span
|
|---|
| 1437 | class="cmtt-8"> 1</span><span
|
|---|
| 1438 | class="cmtt-8"> 0</span><span
|
|---|
| 1439 | class="cmtt-8"> 0</span><span
|
|---|
| 1440 | class="cmtt-8"> 0]</span>
|
|---|
| 1441 | <br class="fancyvrb" /><a
|
|---|
| 1442 | id="x1-43078r7"></a><span
|
|---|
| 1443 | class="cmr-6">7</span><span
|
|---|
| 1444 | class="cmtt-8">byte</span><span
|
|---|
| 1445 | class="cmtt-8"> 2</span><span
|
|---|
| 1446 | class="cmtt-8"> [1</span><span
|
|---|
| 1447 | class="cmtt-8"> 1</span><span
|
|---|
| 1448 | class="cmtt-8"> 0</span><span
|
|---|
| 1449 | class="cmtt-8"> 0</span><span
|
|---|
| 1450 | class="cmtt-8"> 1</span><span
|
|---|
| 1451 | class="cmtt-8"> 1</span><span
|
|---|
| 1452 | class="cmtt-8"> 1</span><span
|
|---|
| 1453 | class="cmtt-8"> 0]</span><br class="fancyvrb" /><a
|
|---|
| 1454 | id="x1-43080r8"></a><span
|
|---|
| 1455 | class="cmr-6">8</span><span
|
|---|
| 1456 | class="cmtt-8">byte</span><span
|
|---|
| 1457 | class="cmtt-8"> 3</span><span
|
|---|
| 1458 | class="cmtt-8"> [0</span><span
|
|---|
| 1459 | class="cmtt-8"> 0</span><span
|
|---|
| 1460 | class="cmtt-8"> 0</span><span
|
|---|
| 1461 | class="cmtt-8"> 0</span><span
|
|---|
| 1462 | class="cmtt-8"> 0</span><span
|
|---|
| 1463 | class="cmtt-8"> 1</span><span
|
|---|
| 1464 | class="cmtt-8"> 1</span><span
|
|---|
| 1465 | class="cmtt-8"> 0]</span><span
|
|---|
| 1466 | class="cmtt-8"> </span><span
|
|---|
| 1467 | class="cmtt-8"> <-</span><br class="fancyvrb" /><a
|
|---|
| 1468 | id="x1-43082r9"></a><span
|
|---|
| 1469 | class="cmr-6">9</span><span
|
|---|
| 1470 | class="cmtt-8"> </span><span
|
|---|
| 1471 | class="cmtt-8"> </span><span
|
|---|
| 1472 | class="cmtt-8"> </span><span
|
|---|
| 1473 | class="cmtt-8"> </span><span
|
|---|
| 1474 | class="cmtt-8"> </span><span
|
|---|
| 1475 | class="cmtt-8"> </span><span
|
|---|
| 1476 | class="cmtt-8"> </span><span
|
|---|
| 1477 | class="cmtt-8"> </span><span
|
|---|
| 1478 | class="cmtt-8"> </span><span
|
|---|
| 1479 | class="cmtt-8"> </span><span
|
|---|
| 1480 | class="cmtt-8"> </span><span
|
|---|
| 1481 | class="cmtt-8"> </span><span
|
|---|
| 1482 | class="cmtt-8"> ...</span><br class="fancyvrb" /><a
|
|---|
| 1483 | id="x1-43084r10"></a><span
|
|---|
| 1484 | class="cmr-6">10</span><span
|
|---|
| 1485 | class="cmtt-8">byte</span><span
|
|---|
| 1486 | class="cmtt-8"> n</span><span
|
|---|
| 1487 | class="cmtt-8"> [</span><span
|
|---|
| 1488 | class="cmtt-8"> </span><span
|
|---|
| 1489 | class="cmtt-8"> </span><span
|
|---|
| 1490 | class="cmtt-8"> </span><span
|
|---|
| 1491 | class="cmtt-8"> </span><span
|
|---|
| 1492 | class="cmtt-8"> </span><span
|
|---|
| 1493 | class="cmtt-8"> </span><span
|
|---|
| 1494 | class="cmtt-8"> </span><span
|
|---|
| 1495 | class="cmtt-8"> </span><span
|
|---|
| 1496 | class="cmtt-8"> </span><span
|
|---|
| 1497 | class="cmtt-8"> </span><span
|
|---|
| 1498 | class="cmtt-8"> </span><span
|
|---|
| 1499 | class="cmtt-8"> </span><span
|
|---|
| 1500 | class="cmtt-8"> </span><span
|
|---|
| 1501 | class="cmtt-8"> </span><span
|
|---|
| 1502 | class="cmtt-8"> ]</span><span
|
|---|
| 1503 | class="cmtt-8"> </span><span
|
|---|
| 1504 | class="cmtt-8"> bytestream</span><span
|
|---|
| 1505 | class="cmtt-8"> length</span><span
|
|---|
| 1506 | class="cmtt-8"> ==</span><span
|
|---|
| 1507 | class="cmtt-8"> 4</span><span
|
|---|
| 1508 | class="cmtt-8"> bytes</span><br class="fancyvrb" /><a
|
|---|
| 1509 | id="x1-43086r11"></a><span
|
|---|
| 1510 | class="cmr-6">11</span></div>
|
|---|
| 1511 |
|
|---|
| 1512 |
|
|---|
| 1513 |
|
|---|
| 1514 | <!--l. 172--><p class="noindent" >
|
|---|
| 1515 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.7. </span> <a
|
|---|
| 1516 | id="x1-440002.1.7"></a>decoding example</h5>
|
|---|
| 1517 | <!--l. 174--><p class="noindent" >Reading from the beginning of the bytestream encoded in the above example:
|
|---|
| 1518 | <!--l. 176--><p class="noindent" >
|
|---|
| 1519 | <div class="fancyvrb" id="fancyvrb6"><a
|
|---|
| 1520 | id="x1-44002r1"></a><span
|
|---|
| 1521 | class="cmr-6">1</span><span
|
|---|
| 1522 | class="cmtt-8"> </span><span
|
|---|
| 1523 | class="cmtt-8"> </span><span
|
|---|
| 1524 | class="cmtt-8"> </span><span
|
|---|
| 1525 | class="cmtt-8"> </span><span
|
|---|
| 1526 | class="cmtt-8"> </span><span
|
|---|
| 1527 | class="cmtt-8"> </span><span
|
|---|
| 1528 | class="cmtt-8"> </span><span
|
|---|
| 1529 | class="cmtt-8"> </span><span
|
|---|
| 1530 | class="cmtt-8"> </span><span
|
|---|
| 1531 | class="cmtt-8"> </span><span
|
|---|
| 1532 | class="cmtt-8"> </span><span
|
|---|
| 1533 | class="cmtt-8"> </span><span
|
|---|
| 1534 | class="cmtt-8"> </span><span
|
|---|
| 1535 | class="cmtt-8"> </span><span
|
|---|
| 1536 | class="cmtt-8"> </span><span
|
|---|
| 1537 | class="cmtt-8"> </span><span
|
|---|
| 1538 | class="cmtt-8"> </span><span
|
|---|
| 1539 | class="cmtt-8"> </span><span
|
|---|
| 1540 | class="cmtt-8"> </span><span
|
|---|
| 1541 | class="cmtt-8"> </span><span
|
|---|
| 1542 | class="cmtt-8"> </span><span
|
|---|
| 1543 | class="cmtt-8"> |</span><br class="fancyvrb" /><a
|
|---|
| 1544 | id="x1-44004r2"></a><span
|
|---|
| 1545 | class="cmr-6">2</span><span
|
|---|
| 1546 | class="cmtt-8"> </span><span
|
|---|
| 1547 | class="cmtt-8"> </span><span
|
|---|
| 1548 | class="cmtt-8"> </span><span
|
|---|
| 1549 | class="cmtt-8"> </span><span
|
|---|
| 1550 | class="cmtt-8"> </span><span
|
|---|
| 1551 | class="cmtt-8"> </span><span
|
|---|
| 1552 | class="cmtt-8"> </span><span
|
|---|
| 1553 | class="cmtt-8"> </span><span
|
|---|
| 1554 | class="cmtt-8"> </span><span
|
|---|
| 1555 | class="cmtt-8"> </span><span
|
|---|
| 1556 | class="cmtt-8"> </span><span
|
|---|
| 1557 | class="cmtt-8"> </span><span
|
|---|
| 1558 | class="cmtt-8"> </span><span
|
|---|
| 1559 | class="cmtt-8"> </span><span
|
|---|
| 1560 | class="cmtt-8"> </span><span
|
|---|
| 1561 | class="cmtt-8"> </span><span
|
|---|
| 1562 | class="cmtt-8"> </span><span
|
|---|
| 1563 | class="cmtt-8"> </span><span
|
|---|
| 1564 | class="cmtt-8"> </span><span
|
|---|
| 1565 | class="cmtt-8"> </span><span
|
|---|
| 1566 | class="cmtt-8"> </span><span
|
|---|
| 1567 | class="cmtt-8"> V</span><br class="fancyvrb" /><a
|
|---|
| 1568 | id="x1-44006r3"></a><span
|
|---|
| 1569 | class="cmr-6">3</span><br class="fancyvrb" /><a
|
|---|
| 1570 | id="x1-44008r4"></a><span
|
|---|
| 1571 | class="cmr-6">4</span><span
|
|---|
| 1572 | class="cmtt-8"> </span><span
|
|---|
| 1573 | class="cmtt-8"> </span><span
|
|---|
| 1574 | class="cmtt-8"> </span><span
|
|---|
| 1575 | class="cmtt-8"> </span><span
|
|---|
| 1576 | class="cmtt-8"> </span><span
|
|---|
| 1577 | class="cmtt-8"> </span><span
|
|---|
| 1578 | class="cmtt-8"> </span><span
|
|---|
| 1579 | class="cmtt-8"> 7</span><span
|
|---|
| 1580 | class="cmtt-8"> 6</span><span
|
|---|
| 1581 | class="cmtt-8"> 5</span><span
|
|---|
| 1582 | class="cmtt-8"> 4</span><span
|
|---|
| 1583 | class="cmtt-8"> 3</span><span
|
|---|
| 1584 | class="cmtt-8"> 2</span><span
|
|---|
| 1585 | class="cmtt-8"> 1</span><span
|
|---|
| 1586 | class="cmtt-8"> 0</span><br class="fancyvrb" /><a
|
|---|
| 1587 | id="x1-44010r5"></a><span
|
|---|
| 1588 | class="cmr-6">5</span><span
|
|---|
| 1589 | class="cmtt-8">byte</span><span
|
|---|
| 1590 | class="cmtt-8"> 0</span><span
|
|---|
| 1591 | class="cmtt-8"> [1</span><span
|
|---|
| 1592 | class="cmtt-8"> 1</span><span
|
|---|
| 1593 | class="cmtt-8"> 1</span><span
|
|---|
| 1594 | class="cmtt-8"> 1</span><span
|
|---|
| 1595 | class="cmtt-8"> 1</span><span
|
|---|
| 1596 | class="cmtt-8"> 1</span><span
|
|---|
| 1597 | class="cmtt-8"> 0</span><span
|
|---|
| 1598 | class="cmtt-8"> 0]</span><span
|
|---|
| 1599 | class="cmtt-8"> </span><span
|
|---|
| 1600 | class="cmtt-8"> <-</span><br class="fancyvrb" /><a
|
|---|
| 1601 | id="x1-44012r6"></a><span
|
|---|
| 1602 | class="cmr-6">6</span><span
|
|---|
| 1603 | class="cmtt-8">byte</span><span
|
|---|
| 1604 | class="cmtt-8"> 1</span><span
|
|---|
| 1605 | class="cmtt-8"> [0</span><span
|
|---|
| 1606 | class="cmtt-8"> 1</span><span
|
|---|
| 1607 | class="cmtt-8"> 0</span><span
|
|---|
| 1608 | class="cmtt-8"> 0</span><span
|
|---|
| 1609 | class="cmtt-8"> 1</span><span
|
|---|
| 1610 | class="cmtt-8"> 0</span><span
|
|---|
| 1611 | class="cmtt-8"> 0</span><span
|
|---|
| 1612 | class="cmtt-8"> 0]</span>
|
|---|
| 1613 | <br class="fancyvrb" /><a
|
|---|
| 1614 | id="x1-44014r7"></a><span
|
|---|
| 1615 | class="cmr-6">7</span><span
|
|---|
| 1616 | class="cmtt-8">byte</span><span
|
|---|
| 1617 | class="cmtt-8"> 2</span><span
|
|---|
| 1618 | class="cmtt-8"> [1</span><span
|
|---|
| 1619 | class="cmtt-8"> 1</span><span
|
|---|
| 1620 | class="cmtt-8"> 0</span><span
|
|---|
| 1621 | class="cmtt-8"> 0</span><span
|
|---|
| 1622 | class="cmtt-8"> 1</span><span
|
|---|
| 1623 | class="cmtt-8"> 1</span><span
|
|---|
| 1624 | class="cmtt-8"> 1</span><span
|
|---|
| 1625 | class="cmtt-8"> 0]</span><br class="fancyvrb" /><a
|
|---|
| 1626 | id="x1-44016r8"></a><span
|
|---|
| 1627 | class="cmr-6">8</span><span
|
|---|
| 1628 | class="cmtt-8">byte</span><span
|
|---|
| 1629 | class="cmtt-8"> 3</span><span
|
|---|
| 1630 | class="cmtt-8"> [0</span><span
|
|---|
| 1631 | class="cmtt-8"> 0</span><span
|
|---|
| 1632 | class="cmtt-8"> 0</span><span
|
|---|
| 1633 | class="cmtt-8"> 0</span><span
|
|---|
| 1634 | class="cmtt-8"> 0</span><span
|
|---|
| 1635 | class="cmtt-8"> 1</span><span
|
|---|
| 1636 | class="cmtt-8"> 1</span><span
|
|---|
| 1637 | class="cmtt-8"> 0]</span><span
|
|---|
| 1638 | class="cmtt-8"> </span><span
|
|---|
| 1639 | class="cmtt-8"> bytestream</span><span
|
|---|
| 1640 | class="cmtt-8"> length</span><span
|
|---|
| 1641 | class="cmtt-8"> ==</span><span
|
|---|
| 1642 | class="cmtt-8"> 4</span><span
|
|---|
| 1643 | class="cmtt-8"> bytes</span><br class="fancyvrb" /><a
|
|---|
| 1644 | id="x1-44018r9"></a><span
|
|---|
| 1645 | class="cmr-6">9</span></div>
|
|---|
| 1646 | <!--l. 189--><p class="noindent" >We read two, two-bit integer fields, resulting in the returned numbers ’b00’ and ’b11’. Two things
|
|---|
| 1647 | are worth noting here:
|
|---|
| 1648 | <ul class="itemize1">
|
|---|
| 1649 | <li class="itemize">Although these four bits were originally written as a single four-bit integer, reading
|
|---|
| 1650 | some other combination of bit-widths from the bitstream is well defined. There are
|
|---|
| 1651 | no artificial alignment boundaries maintained in the bitstream.
|
|---|
| 1652 | </li>
|
|---|
| 1653 | <li class="itemize">The second value is the two-bit-wide integer ’b11’. This value may be interpreted
|
|---|
| 1654 | either as the unsigned value ’3’, or the signed value ’-1’. Signedness is dependent on
|
|---|
| 1655 | decode context.</li></ul>
|
|---|
| 1656 | <!--l. 207--><p class="noindent" >
|
|---|
| 1657 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.8. </span> <a
|
|---|
| 1658 | id="x1-450002.1.8"></a>end-of-packet alignment</h5>
|
|---|
| 1659 | <!--l. 209--><p class="noindent" >The typical use of bitpacking is to produce many independent byte-aligned packets which are
|
|---|
| 1660 | embedded into a larger byte-aligned container structure, such as an Ogg transport bitstream.
|
|---|
| 1661 | Externally, each bytestream (encoded bitstream) must begin and end on a byte boundary. Often,
|
|---|
| 1662 | the encoded bitstream is not an integer number of bytes, and so there is unused (uncoded) space
|
|---|
| 1663 | in the last byte of a packet.
|
|---|
| 1664 | <!--l. 217--><p class="noindent" >Unused space in the last byte of a bytestream is always zeroed during the coding process. Thus,
|
|---|
| 1665 | should this unused space be read, it will return binary zeroes.
|
|---|
| 1666 | <!--l. 221--><p class="noindent" >Attempting to read past the end of an encoded packet results in an ’end-of-packet’ condition.
|
|---|
| 1667 | End-of-packet is not to be considered an error; it is merely a state indicating that there is
|
|---|
| 1668 | insufficient remaining data to fulfill the desired read size. Vorbis uses truncated packets as a
|
|---|
| 1669 |
|
|---|
| 1670 |
|
|---|
| 1671 |
|
|---|
| 1672 | normal mode of operation, and as such, decoders must handle reading past the end of a packet as
|
|---|
| 1673 | a typical mode of operation. Any further read operations after an ’end-of-packet’ condition shall
|
|---|
| 1674 | also return ’end-of-packet’.
|
|---|
| 1675 | <!--l. 232--><p class="noindent" >
|
|---|
| 1676 | <h5 class="subsubsectionHead"><span class="titlemark">2.1.9. </span> <a
|
|---|
| 1677 | id="x1-460002.1.9"></a>reading zero bits</h5>
|
|---|
| 1678 | <!--l. 234--><p class="noindent" >Reading a zero-bit-wide integer returns the value ’0’ and does not increment the stream cursor.
|
|---|
| 1679 | Reading to the end of the packet (but not past, such that an ’end-of-packet’ condition has not
|
|---|
| 1680 | triggered) and then reading a zero bit integer shall succeed, returning 0, and not trigger an
|
|---|
| 1681 | end-of-packet condition. Reading a zero-bit-wide integer after a previous read sets ’end-of-packet’
|
|---|
| 1682 | shall also fail with ’end-of-packet’.
|
|---|
| 1683 |
|
|---|
| 1684 |
|
|---|
| 1685 |
|
|---|
| 1686 |
|
|---|
| 1687 |
|
|---|
| 1688 |
|
|---|
| 1689 | <h3 class="sectionHead"><span class="titlemark">3. </span> <a
|
|---|
| 1690 | id="x1-470003"></a>Probability Model and Codebooks</h3>
|
|---|
| 1691 | <!--l. 5--><p class="noindent" >
|
|---|
| 1692 | <h4 class="subsectionHead"><span class="titlemark">3.1. </span> <a
|
|---|
| 1693 | id="x1-480003.1"></a>Overview</h4>
|
|---|
| 1694 | <!--l. 7--><p class="noindent" >Unlike practically every other mainstream audio codec, Vorbis has no statically configured
|
|---|
| 1695 | probability model, instead packing all entropy decoding configuration, VQ and Huffman, into the
|
|---|
| 1696 | bitstream itself in the third header, the codec setup header. This packed configuration consists of
|
|---|
| 1697 | multiple ’codebooks’, each containing a specific Huffman-equivalent representation for decoding
|
|---|
| 1698 | compressed codewords as well as an optional lookup table of output vector values to which a
|
|---|
| 1699 | decoded Huffman value is applied as an offset, generating the final decoded output corresponding
|
|---|
| 1700 | to a given compressed codeword.
|
|---|
| 1701 | <!--l. 17--><p class="noindent" >
|
|---|
| 1702 | <h5 class="subsubsectionHead"><span class="titlemark">3.1.1. </span> <a
|
|---|
| 1703 | id="x1-490003.1.1"></a>Bitwise operation</h5>
|
|---|
| 1704 | <!--l. 18--><p class="noindent" >The codebook mechanism is built on top of the vorbis bitpacker. Both the codebooks themselves
|
|---|
| 1705 | and the codewords they decode are unrolled from a packet as a series of arbitrary-width values
|
|---|
| 1706 | read from the stream according to <a
|
|---|
| 1707 | href="#x1-360002">section 2</a>, “<a
|
|---|
| 1708 | href="#x1-360002">Bitpacking Convention<!--tex4ht:ref: vorbis:spec:bitpacking --></a>”.
|
|---|
| 1709 | <!--l. 26--><p class="noindent" >
|
|---|
| 1710 | <h4 class="subsectionHead"><span class="titlemark">3.2. </span> <a
|
|---|
| 1711 | id="x1-500003.2"></a>Packed codebook format</h4>
|
|---|
| 1712 | <!--l. 28--><p class="noindent" >For purposes of the examples below, we assume that the storage system’s native byte width is
|
|---|
| 1713 | eight bits. This is not universally true; see <a
|
|---|
| 1714 | href="#x1-360002">section 2</a>, “<a
|
|---|
| 1715 | href="#x1-360002">Bitpacking Convention<!--tex4ht:ref: vorbis:spec:bitpacking --></a>” for discussion
|
|---|
| 1716 | relating to non-eight-bit bytes.
|
|---|
| 1717 |
|
|---|
| 1718 |
|
|---|
| 1719 |
|
|---|
| 1720 | <!--l. 33--><p class="noindent" >
|
|---|
| 1721 | <h5 class="subsubsectionHead"><span class="titlemark">3.2.1. </span> <a
|
|---|
| 1722 | id="x1-510003.2.1"></a>codebook decode</h5>
|
|---|
| 1723 | <!--l. 35--><p class="noindent" >A codebook begins with a 24 bit sync pattern, 0x564342:
|
|---|
| 1724 | <!--l. 37--><p class="noindent" >
|
|---|
| 1725 | <div class="fancyvrb" id="fancyvrb7"><a
|
|---|
| 1726 | id="x1-51002r1"></a><span
|
|---|
| 1727 | class="cmr-6">1</span><span
|
|---|
| 1728 | class="cmtt-8">byte</span><span
|
|---|
| 1729 | class="cmtt-8"> 0:</span><span
|
|---|
| 1730 | class="cmtt-8"> [</span><span
|
|---|
| 1731 | class="cmtt-8"> 0</span><span
|
|---|
| 1732 | class="cmtt-8"> 1</span><span
|
|---|
| 1733 | class="cmtt-8"> 0</span><span
|
|---|
| 1734 | class="cmtt-8"> 0</span><span
|
|---|
| 1735 | class="cmtt-8"> 0</span><span
|
|---|
| 1736 | class="cmtt-8"> 0</span><span
|
|---|
| 1737 | class="cmtt-8"> 1</span><span
|
|---|
| 1738 | class="cmtt-8"> 0</span><span
|
|---|
| 1739 | class="cmtt-8"> ]</span><span
|
|---|
| 1740 | class="cmtt-8"> (0x42)</span><br class="fancyvrb" /><a
|
|---|
| 1741 | id="x1-51004r2"></a><span
|
|---|
| 1742 | class="cmr-6">2</span><span
|
|---|
| 1743 | class="cmtt-8">byte</span><span
|
|---|
| 1744 | class="cmtt-8"> 1:</span><span
|
|---|
| 1745 | class="cmtt-8"> [</span><span
|
|---|
| 1746 | class="cmtt-8"> 0</span><span
|
|---|
| 1747 | class="cmtt-8"> 1</span><span
|
|---|
| 1748 | class="cmtt-8"> 0</span><span
|
|---|
| 1749 | class="cmtt-8"> 0</span><span
|
|---|
| 1750 | class="cmtt-8"> 0</span><span
|
|---|
| 1751 | class="cmtt-8"> 0</span><span
|
|---|
| 1752 | class="cmtt-8"> 1</span><span
|
|---|
| 1753 | class="cmtt-8"> 1</span><span
|
|---|
| 1754 | class="cmtt-8"> ]</span><span
|
|---|
| 1755 | class="cmtt-8"> (0x43)</span><br class="fancyvrb" /><a
|
|---|
| 1756 | id="x1-51006r3"></a><span
|
|---|
| 1757 | class="cmr-6">3</span><span
|
|---|
| 1758 | class="cmtt-8">byte</span><span
|
|---|
| 1759 | class="cmtt-8"> 2:</span><span
|
|---|
| 1760 | class="cmtt-8"> [</span><span
|
|---|
| 1761 | class="cmtt-8"> 0</span><span
|
|---|
| 1762 | class="cmtt-8"> 1</span><span
|
|---|
| 1763 | class="cmtt-8"> 0</span><span
|
|---|
| 1764 | class="cmtt-8"> 1</span><span
|
|---|
| 1765 | class="cmtt-8"> 0</span><span
|
|---|
| 1766 | class="cmtt-8"> 1</span><span
|
|---|
| 1767 | class="cmtt-8"> 1</span><span
|
|---|
| 1768 | class="cmtt-8"> 0</span><span
|
|---|
| 1769 | class="cmtt-8"> ]</span><span
|
|---|
| 1770 | class="cmtt-8"> (0x56)</span></div>
|
|---|
| 1771 | <!--l. 43--><p class="noindent" >16 bit <span
|
|---|
| 1772 | class="cmtt-12">[codebook</span><span
|
|---|
| 1773 | class="cmtt-12">_dimensions] </span>and 24 bit <span
|
|---|
| 1774 | class="cmtt-12">[codebook</span><span
|
|---|
| 1775 | class="cmtt-12">_entries] </span>fields:
|
|---|
| 1776 | <!--l. 45--><p class="noindent" >
|
|---|
| 1777 | <div class="fancyvrb" id="fancyvrb8"><a
|
|---|
| 1778 | id="x1-51008r1"></a><span
|
|---|
| 1779 | class="cmr-6">1</span><br class="fancyvrb" /><a
|
|---|
| 1780 | id="x1-51010r2"></a><span
|
|---|
| 1781 | class="cmr-6">2</span><span
|
|---|
| 1782 | class="cmtt-8">byte</span><span
|
|---|
| 1783 | class="cmtt-8"> 3:</span><span
|
|---|
| 1784 | class="cmtt-8"> [</span><span
|
|---|
| 1785 | class="cmtt-8"> X</span><span
|
|---|
| 1786 | class="cmtt-8"> X</span><span
|
|---|
| 1787 | class="cmtt-8"> X</span><span
|
|---|
| 1788 | class="cmtt-8"> X</span><span
|
|---|
| 1789 | class="cmtt-8"> X</span><span
|
|---|
| 1790 | class="cmtt-8"> X</span><span
|
|---|
| 1791 | class="cmtt-8"> X</span><span
|
|---|
| 1792 | class="cmtt-8"> X</span><span
|
|---|
| 1793 | class="cmtt-8"> ]</span><br class="fancyvrb" /><a
|
|---|
| 1794 | id="x1-51012r3"></a><span
|
|---|
| 1795 | class="cmr-6">3</span><span
|
|---|
| 1796 | class="cmtt-8">byte</span><span
|
|---|
| 1797 | class="cmtt-8"> 4:</span><span
|
|---|
| 1798 | class="cmtt-8"> [</span><span
|
|---|
| 1799 | class="cmtt-8"> X</span><span
|
|---|
| 1800 | class="cmtt-8"> X</span><span
|
|---|
| 1801 | class="cmtt-8"> X</span><span
|
|---|
| 1802 | class="cmtt-8"> X</span><span
|
|---|
| 1803 | class="cmtt-8"> X</span><span
|
|---|
| 1804 | class="cmtt-8"> X</span><span
|
|---|
| 1805 | class="cmtt-8"> X</span><span
|
|---|
| 1806 | class="cmtt-8"> X</span><span
|
|---|
| 1807 | class="cmtt-8"> ]</span><span
|
|---|
| 1808 | class="cmtt-8"> [codebook</span><span
|
|---|
| 1809 | class="cmtt-8">_dimensions]</span><span
|
|---|
| 1810 | class="cmtt-8"> (16</span><span
|
|---|
| 1811 | class="cmtt-8"> bit</span><span
|
|---|
| 1812 | class="cmtt-8"> unsigned)</span><br class="fancyvrb" /><a
|
|---|
| 1813 | id="x1-51014r4"></a><span
|
|---|
| 1814 | class="cmr-6">4</span><br class="fancyvrb" /><a
|
|---|
| 1815 | id="x1-51016r5"></a><span
|
|---|
| 1816 | class="cmr-6">5</span><span
|
|---|
| 1817 | class="cmtt-8">byte</span><span
|
|---|
| 1818 | class="cmtt-8"> 5:</span><span
|
|---|
| 1819 | class="cmtt-8"> [</span><span
|
|---|
| 1820 | class="cmtt-8"> X</span><span
|
|---|
| 1821 | class="cmtt-8"> X</span><span
|
|---|
| 1822 | class="cmtt-8"> X</span><span
|
|---|
| 1823 | class="cmtt-8"> X</span><span
|
|---|
| 1824 | class="cmtt-8"> X</span><span
|
|---|
| 1825 | class="cmtt-8"> X</span><span
|
|---|
| 1826 | class="cmtt-8"> X</span><span
|
|---|
| 1827 | class="cmtt-8"> X</span><span
|
|---|
| 1828 | class="cmtt-8"> ]</span>
|
|---|
| 1829 | <br class="fancyvrb" /><a
|
|---|
| 1830 | id="x1-51018r6"></a><span
|
|---|
| 1831 | class="cmr-6">6</span><span
|
|---|
| 1832 | class="cmtt-8">byte</span><span
|
|---|
| 1833 | class="cmtt-8"> 6:</span><span
|
|---|
| 1834 | class="cmtt-8"> [</span><span
|
|---|
| 1835 | class="cmtt-8"> X</span><span
|
|---|
| 1836 | class="cmtt-8"> X</span><span
|
|---|
| 1837 | class="cmtt-8"> X</span><span
|
|---|
| 1838 | class="cmtt-8"> X</span><span
|
|---|
| 1839 | class="cmtt-8"> X</span><span
|
|---|
| 1840 | class="cmtt-8"> X</span><span
|
|---|
| 1841 | class="cmtt-8"> X</span><span
|
|---|
| 1842 | class="cmtt-8"> X</span><span
|
|---|
| 1843 | class="cmtt-8"> ]</span><br class="fancyvrb" /><a
|
|---|
| 1844 | id="x1-51020r7"></a><span
|
|---|
| 1845 | class="cmr-6">7</span><span
|
|---|
| 1846 | class="cmtt-8">byte</span><span
|
|---|
| 1847 | class="cmtt-8"> 7:</span><span
|
|---|
| 1848 | class="cmtt-8"> [</span><span
|
|---|
| 1849 | class="cmtt-8"> X</span><span
|
|---|
| 1850 | class="cmtt-8"> X</span><span
|
|---|
| 1851 | class="cmtt-8"> X</span><span
|
|---|
| 1852 | class="cmtt-8"> X</span><span
|
|---|
| 1853 | class="cmtt-8"> X</span><span
|
|---|
| 1854 | class="cmtt-8"> X</span><span
|
|---|
| 1855 | class="cmtt-8"> X</span><span
|
|---|
| 1856 | class="cmtt-8"> X</span><span
|
|---|
| 1857 | class="cmtt-8"> ]</span><span
|
|---|
| 1858 | class="cmtt-8"> [codebook</span><span
|
|---|
| 1859 | class="cmtt-8">_entries]</span><span
|
|---|
| 1860 | class="cmtt-8"> (24</span><span
|
|---|
| 1861 | class="cmtt-8"> bit</span><span
|
|---|
| 1862 | class="cmtt-8"> unsigned)</span><br class="fancyvrb" /><a
|
|---|
| 1863 | id="x1-51022r8"></a><span
|
|---|
| 1864 | class="cmr-6">8</span></div>
|
|---|
| 1865 | <!--l. 56--><p class="noindent" >Next is the <span
|
|---|
| 1866 | class="cmtt-12">[ordered] </span>bit flag:
|
|---|
| 1867 | <!--l. 58--><p class="noindent" >
|
|---|
| 1868 | <div class="fancyvrb" id="fancyvrb9"><a
|
|---|
| 1869 | id="x1-51024r1"></a><span
|
|---|
| 1870 | class="cmr-6">1</span><br class="fancyvrb" /><a
|
|---|
| 1871 | id="x1-51026r2"></a><span
|
|---|
| 1872 | class="cmr-6">2</span><span
|
|---|
| 1873 | class="cmtt-8">byte</span><span
|
|---|
| 1874 | class="cmtt-8"> 8:</span><span
|
|---|
| 1875 | class="cmtt-8"> [</span><span
|
|---|
| 1876 | class="cmtt-8"> </span><span
|
|---|
| 1877 | class="cmtt-8"> </span><span
|
|---|
| 1878 | class="cmtt-8"> </span><span
|
|---|
| 1879 | class="cmtt-8"> </span><span
|
|---|
| 1880 | class="cmtt-8"> </span><span
|
|---|
| 1881 | class="cmtt-8"> </span><span
|
|---|
| 1882 | class="cmtt-8"> </span><span
|
|---|
| 1883 | class="cmtt-8"> </span><span
|
|---|
| 1884 | class="cmtt-8"> </span><span
|
|---|
| 1885 | class="cmtt-8"> </span><span
|
|---|
| 1886 | class="cmtt-8"> </span><span
|
|---|
| 1887 | class="cmtt-8"> </span><span
|
|---|
| 1888 | class="cmtt-8"> </span><span
|
|---|
| 1889 | class="cmtt-8"> </span><span
|
|---|
| 1890 | class="cmtt-8"> X</span><span
|
|---|
| 1891 | class="cmtt-8"> ]</span><span
|
|---|
| 1892 | class="cmtt-8"> [ordered]</span><span
|
|---|
| 1893 | class="cmtt-8"> (1</span><span
|
|---|
| 1894 | class="cmtt-8"> bit)</span><br class="fancyvrb" /><a
|
|---|
| 1895 | id="x1-51028r3"></a><span
|
|---|
| 1896 | class="cmr-6">3</span></div>
|
|---|
| 1897 | <!--l. 64--><p class="noindent" >Each entry, numbering a total of <span
|
|---|
| 1898 | class="cmtt-12">[codebook</span><span
|
|---|
| 1899 | class="cmtt-12">_entries]</span>, is assigned a codeword length.
|
|---|
| 1900 | We now read the list of codeword lengths and store these lengths in the array
|
|---|
| 1901 | <span
|
|---|
| 1902 | class="cmtt-12">[codebook</span><span
|
|---|
| 1903 | class="cmtt-12">_codeword</span><span
|
|---|
| 1904 | class="cmtt-12">_lengths]</span>. Decode of lengths is according to whether the <span
|
|---|
| 1905 | class="cmtt-12">[ordered] </span>flag
|
|---|
| 1906 | is set or unset.
|
|---|
| 1907 | <ul class="itemize1">
|
|---|
| 1908 | <li class="itemize">If the <span
|
|---|
| 1909 | class="cmtt-12">[ordered] </span>flag is unset, the codeword list is not length ordered and the decoder
|
|---|
| 1910 | needs to read each codeword length one-by-one.
|
|---|
| 1911 | <!--l. 76--><p class="noindent" >The decoder first reads one additional bit flag, the <span
|
|---|
| 1912 | class="cmtt-12">[sparse] </span>flag. This flag determines
|
|---|
| 1913 | whether or not the codebook contains unused entries that are not to be included in
|
|---|
| 1914 | the codeword decode tree:
|
|---|
| 1915 | <!--l. 81--><p class="noindent" >
|
|---|
| 1916 | <div class="fancyvrb" id="fancyvrb10"><a
|
|---|
| 1917 | id="x1-51030r1"></a><span
|
|---|
| 1918 | class="cmr-6">1</span><span
|
|---|
| 1919 | class="cmtt-8">byte</span><span
|
|---|
| 1920 | class="cmtt-8"> 8:</span><span
|
|---|
| 1921 | class="cmtt-8"> [</span><span
|
|---|
| 1922 | class="cmtt-8"> </span><span
|
|---|
| 1923 | class="cmtt-8"> </span><span
|
|---|
| 1924 | class="cmtt-8"> </span><span
|
|---|
| 1925 | class="cmtt-8"> </span><span
|
|---|
| 1926 | class="cmtt-8"> </span><span
|
|---|
| 1927 | class="cmtt-8"> </span><span
|
|---|
| 1928 | class="cmtt-8"> </span><span
|
|---|
| 1929 | class="cmtt-8"> </span><span
|
|---|
| 1930 | class="cmtt-8"> </span><span
|
|---|
| 1931 | class="cmtt-8"> </span><span
|
|---|
| 1932 | class="cmtt-8"> </span><span
|
|---|
| 1933 | class="cmtt-8"> </span><span
|
|---|
| 1934 | class="cmtt-8"> X</span><span
|
|---|
| 1935 | class="cmtt-8"> 1</span><span
|
|---|
| 1936 | class="cmtt-8"> ]</span><span
|
|---|
| 1937 | class="cmtt-8"> [sparse]</span><span
|
|---|
| 1938 | class="cmtt-8"> flag</span><span
|
|---|
| 1939 | class="cmtt-8"> (1</span><span
|
|---|
| 1940 | class="cmtt-8"> bit)</span></div>
|
|---|
| 1941 | <!--l. 85--><p class="noindent" >The decoder now performs for each of the <span
|
|---|
| 1942 | class="cmtt-12">[codebook</span><span
|
|---|
| 1943 | class="cmtt-12">_entries] </span>codebook entries:
|
|---|
| 1944 | <!--l. 88--><p class="noindent" >
|
|---|
| 1945 | <div class="fancyvrb" id="fancyvrb11"><a
|
|---|
| 1946 | id="x1-51032r1"></a><span
|
|---|
| 1947 | class="cmr-6">1</span><br class="fancyvrb" /><a
|
|---|
| 1948 | id="x1-51034r2"></a><span
|
|---|
| 1949 | class="cmr-6">2</span><span
|
|---|
| 1950 | class="cmtt-8"> </span><span
|
|---|
| 1951 | class="cmtt-8"> 1)</span><span
|
|---|
| 1952 | class="cmtt-8"> if([sparse]</span><span
|
|---|
| 1953 | class="cmtt-8"> is</span><span
|
|---|
| 1954 | class="cmtt-8"> set)</span><span
|
|---|
| 1955 | class="cmtt-8"> </span><span
|
|---|
| 1956 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 1957 | id="x1-51036r3"></a><span
|
|---|
| 1958 | class="cmr-6">3</span><br class="fancyvrb" /><a
|
|---|
| 1959 | id="x1-51038r4"></a><span
|
|---|
| 1960 | class="cmr-6">4</span><span
|
|---|
| 1961 | class="cmtt-8"> </span><span
|
|---|
| 1962 | class="cmtt-8"> </span><span
|
|---|
| 1963 | class="cmtt-8"> </span><span
|
|---|
| 1964 | class="cmtt-8"> </span><span
|
|---|
| 1965 | class="cmtt-8"> </span><span
|
|---|
| 1966 | class="cmtt-8"> </span><span
|
|---|
| 1967 | class="cmtt-8"> </span><span
|
|---|
| 1968 | class="cmtt-8"> </span><span
|
|---|
| 1969 | class="cmtt-8"> 2)</span><span
|
|---|
| 1970 | class="cmtt-8"> [flag]</span><span
|
|---|
| 1971 | class="cmtt-8"> =</span><span
|
|---|
| 1972 | class="cmtt-8"> read</span><span
|
|---|
| 1973 | class="cmtt-8"> one</span><span
|
|---|
| 1974 | class="cmtt-8"> bit;</span><br class="fancyvrb" /><a
|
|---|
| 1975 | id="x1-51040r5"></a><span
|
|---|
| 1976 | class="cmr-6">5</span><span
|
|---|
| 1977 | class="cmtt-8"> </span><span
|
|---|
| 1978 | class="cmtt-8"> </span><span
|
|---|
| 1979 | class="cmtt-8"> </span><span
|
|---|
| 1980 | class="cmtt-8"> </span><span
|
|---|
| 1981 | class="cmtt-8"> </span><span
|
|---|
| 1982 | class="cmtt-8"> </span><span
|
|---|
| 1983 | class="cmtt-8"> </span><span
|
|---|
| 1984 | class="cmtt-8"> </span><span
|
|---|
| 1985 | class="cmtt-8"> 3)</span><span
|
|---|
| 1986 | class="cmtt-8"> if([flag]</span><span
|
|---|
| 1987 | class="cmtt-8"> is</span><span
|
|---|
| 1988 | class="cmtt-8"> set)</span><span
|
|---|
| 1989 | class="cmtt-8"> </span><span
|
|---|
| 1990 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 1991 | id="x1-51042r6"></a><span
|
|---|
| 1992 | class="cmr-6">6</span>
|
|---|
| 1993 | <br class="fancyvrb" /><a
|
|---|
| 1994 | id="x1-51044r7"></a><span
|
|---|
| 1995 | class="cmr-6">7</span><span
|
|---|
| 1996 | class="cmtt-8"> </span><span
|
|---|
| 1997 | class="cmtt-8"> </span><span
|
|---|
| 1998 | class="cmtt-8"> </span><span
|
|---|
| 1999 | class="cmtt-8"> </span><span
|
|---|
| 2000 | class="cmtt-8"> </span><span
|
|---|
| 2001 | class="cmtt-8"> </span><span
|
|---|
| 2002 | class="cmtt-8"> </span><span
|
|---|
| 2003 | class="cmtt-8"> </span><span
|
|---|
| 2004 | class="cmtt-8"> </span><span
|
|---|
| 2005 | class="cmtt-8"> </span><span
|
|---|
| 2006 | class="cmtt-8"> </span><span
|
|---|
| 2007 | class="cmtt-8"> </span><span
|
|---|
| 2008 | class="cmtt-8"> </span><span
|
|---|
| 2009 | class="cmtt-8"> 4)</span><span
|
|---|
| 2010 | class="cmtt-8"> [length]</span><span
|
|---|
| 2011 | class="cmtt-8"> =</span><span
|
|---|
| 2012 | class="cmtt-8"> read</span><span
|
|---|
| 2013 | class="cmtt-8"> a</span><span
|
|---|
| 2014 | class="cmtt-8"> five</span><span
|
|---|
| 2015 | class="cmtt-8"> bit</span><span
|
|---|
| 2016 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2017 | class="cmtt-8"> integer;</span><br class="fancyvrb" /><a
|
|---|
| 2018 | id="x1-51046r8"></a><span
|
|---|
| 2019 | class="cmr-6">8</span><span
|
|---|
| 2020 | class="cmtt-8"> </span><span
|
|---|
| 2021 | class="cmtt-8"> </span><span
|
|---|
| 2022 | class="cmtt-8"> </span><span
|
|---|
| 2023 | class="cmtt-8"> </span><span
|
|---|
| 2024 | class="cmtt-8"> </span><span
|
|---|
| 2025 | class="cmtt-8"> </span><span
|
|---|
| 2026 | class="cmtt-8"> </span><span
|
|---|
| 2027 | class="cmtt-8"> </span><span
|
|---|
| 2028 | class="cmtt-8"> </span><span
|
|---|
| 2029 | class="cmtt-8"> </span><span
|
|---|
| 2030 | class="cmtt-8"> </span><span
|
|---|
| 2031 | class="cmtt-8"> </span><span
|
|---|
| 2032 | class="cmtt-8"> </span><span
|
|---|
| 2033 | class="cmtt-8"> 5)</span><span
|
|---|
| 2034 | class="cmtt-8"> codeword</span><span
|
|---|
| 2035 | class="cmtt-8"> length</span><span
|
|---|
| 2036 | class="cmtt-8"> for</span><span
|
|---|
| 2037 | class="cmtt-8"> this</span><span
|
|---|
| 2038 | class="cmtt-8"> entry</span><span
|
|---|
| 2039 | class="cmtt-8"> is</span><span
|
|---|
| 2040 | class="cmtt-8"> [length]+1;</span><br class="fancyvrb" /><a
|
|---|
| 2041 | id="x1-51048r9"></a><span
|
|---|
| 2042 | class="cmr-6">9</span>
|
|---|
| 2043 | <br class="fancyvrb" /><a
|
|---|
| 2044 | id="x1-51050r10"></a><span
|
|---|
| 2045 | class="cmr-6">10</span><span
|
|---|
| 2046 | class="cmtt-8"> </span><span
|
|---|
| 2047 | class="cmtt-8"> </span><span
|
|---|
| 2048 | class="cmtt-8"> </span><span
|
|---|
| 2049 | class="cmtt-8"> </span><span
|
|---|
| 2050 | class="cmtt-8"> </span><span
|
|---|
| 2051 | class="cmtt-8"> </span><span
|
|---|
| 2052 | class="cmtt-8"> </span><span
|
|---|
| 2053 | class="cmtt-8"> </span><span
|
|---|
| 2054 | class="cmtt-8"> </span><span
|
|---|
| 2055 | class="cmtt-8"> </span><span
|
|---|
| 2056 | class="cmtt-8"> </span><span
|
|---|
| 2057 | class="cmtt-8"> </span><span
|
|---|
| 2058 | class="cmsy-8">}</span><span
|
|---|
| 2059 | class="cmtt-8"> else</span><span
|
|---|
| 2060 | class="cmtt-8"> </span><span
|
|---|
| 2061 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 2062 | id="x1-51052r11"></a><span
|
|---|
| 2063 | class="cmr-6">11</span><br class="fancyvrb" /><a
|
|---|
| 2064 | id="x1-51054r12"></a><span
|
|---|
| 2065 | class="cmr-6">12</span><span
|
|---|
| 2066 | class="cmtt-8"> </span><span
|
|---|
| 2067 | class="cmtt-8"> </span><span
|
|---|
| 2068 | class="cmtt-8"> </span><span
|
|---|
| 2069 | class="cmtt-8"> </span><span
|
|---|
| 2070 | class="cmtt-8"> </span><span
|
|---|
| 2071 | class="cmtt-8"> </span><span
|
|---|
| 2072 | class="cmtt-8"> </span><span
|
|---|
| 2073 | class="cmtt-8"> </span><span
|
|---|
| 2074 | class="cmtt-8"> </span><span
|
|---|
| 2075 | class="cmtt-8"> </span><span
|
|---|
| 2076 | class="cmtt-8"> </span><span
|
|---|
| 2077 | class="cmtt-8"> </span><span
|
|---|
| 2078 | class="cmtt-8"> </span><span
|
|---|
| 2079 | class="cmtt-8"> 6)</span><span
|
|---|
| 2080 | class="cmtt-8"> this</span><span
|
|---|
| 2081 | class="cmtt-8"> entry</span><span
|
|---|
| 2082 | class="cmtt-8"> is</span><span
|
|---|
| 2083 | class="cmtt-8"> unused.</span><span
|
|---|
| 2084 | class="cmtt-8"> </span><span
|
|---|
| 2085 | class="cmtt-8"> mark</span><span
|
|---|
| 2086 | class="cmtt-8"> it</span><span
|
|---|
| 2087 | class="cmtt-8"> as</span><span
|
|---|
| 2088 | class="cmtt-8"> such.</span><br class="fancyvrb" /><a
|
|---|
| 2089 | id="x1-51056r13"></a><span
|
|---|
| 2090 | class="cmr-6">13</span><br class="fancyvrb" /><a
|
|---|
| 2091 | id="x1-51058r14"></a><span
|
|---|
| 2092 | class="cmr-6">14</span><span
|
|---|
| 2093 | class="cmtt-8"> </span><span
|
|---|
| 2094 | class="cmtt-8"> </span><span
|
|---|
| 2095 | class="cmtt-8"> </span><span
|
|---|
| 2096 | class="cmtt-8"> </span><span
|
|---|
| 2097 | class="cmtt-8"> </span><span
|
|---|
| 2098 | class="cmtt-8"> </span><span
|
|---|
| 2099 | class="cmtt-8"> </span><span
|
|---|
| 2100 | class="cmtt-8"> </span><span
|
|---|
| 2101 | class="cmtt-8"> </span><span
|
|---|
| 2102 | class="cmtt-8"> </span><span
|
|---|
| 2103 | class="cmtt-8"> </span><span
|
|---|
| 2104 | class="cmtt-8"> </span><span
|
|---|
| 2105 | class="cmsy-8">}</span><br class="fancyvrb" /><a
|
|---|
| 2106 | id="x1-51060r15"></a><span
|
|---|
| 2107 | class="cmr-6">15</span><br class="fancyvrb" /><a
|
|---|
| 2108 | id="x1-51062r16"></a><span
|
|---|
| 2109 | class="cmr-6">16</span><span
|
|---|
| 2110 | class="cmtt-8"> </span><span
|
|---|
| 2111 | class="cmtt-8"> </span><span
|
|---|
| 2112 | class="cmtt-8"> </span><span
|
|---|
| 2113 | class="cmtt-8"> </span><span
|
|---|
| 2114 | class="cmtt-8"> </span><span
|
|---|
| 2115 | class="cmsy-8">}</span><span
|
|---|
| 2116 | class="cmtt-8"> else</span><span
|
|---|
| 2117 | class="cmtt-8"> the</span><span
|
|---|
| 2118 | class="cmtt-8"> sparse</span><span
|
|---|
| 2119 | class="cmtt-8"> flag</span><span
|
|---|
| 2120 | class="cmtt-8"> is</span><span
|
|---|
| 2121 | class="cmtt-8"> not</span><span
|
|---|
| 2122 | class="cmtt-8"> set</span><span
|
|---|
| 2123 | class="cmtt-8"> </span><span
|
|---|
| 2124 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 2125 | id="x1-51064r17"></a><span
|
|---|
| 2126 | class="cmr-6">17</span>
|
|---|
| 2127 | <br class="fancyvrb" /><a
|
|---|
| 2128 | id="x1-51066r18"></a><span
|
|---|
| 2129 | class="cmr-6">18</span><span
|
|---|
| 2130 | class="cmtt-8"> </span><span
|
|---|
| 2131 | class="cmtt-8"> </span><span
|
|---|
| 2132 | class="cmtt-8"> </span><span
|
|---|
| 2133 | class="cmtt-8"> </span><span
|
|---|
| 2134 | class="cmtt-8"> </span><span
|
|---|
| 2135 | class="cmtt-8"> </span><span
|
|---|
| 2136 | class="cmtt-8"> </span><span
|
|---|
| 2137 | class="cmtt-8"> 7)</span><span
|
|---|
| 2138 | class="cmtt-8"> [length]</span><span
|
|---|
| 2139 | class="cmtt-8"> =</span><span
|
|---|
| 2140 | class="cmtt-8"> read</span><span
|
|---|
| 2141 | class="cmtt-8"> a</span><span
|
|---|
| 2142 | class="cmtt-8"> five</span><span
|
|---|
| 2143 | class="cmtt-8"> bit</span><span
|
|---|
| 2144 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2145 | class="cmtt-8"> integer;</span><br class="fancyvrb" /><a
|
|---|
| 2146 | id="x1-51068r19"></a><span
|
|---|
| 2147 | class="cmr-6">19</span><span
|
|---|
| 2148 | class="cmtt-8"> </span><span
|
|---|
| 2149 | class="cmtt-8"> </span><span
|
|---|
| 2150 | class="cmtt-8"> </span><span
|
|---|
| 2151 | class="cmtt-8"> </span><span
|
|---|
| 2152 | class="cmtt-8"> </span><span
|
|---|
| 2153 | class="cmtt-8"> </span><span
|
|---|
| 2154 | class="cmtt-8"> </span><span
|
|---|
| 2155 | class="cmtt-8"> 8)</span><span
|
|---|
| 2156 | class="cmtt-8"> the</span><span
|
|---|
| 2157 | class="cmtt-8"> codeword</span><span
|
|---|
| 2158 | class="cmtt-8"> length</span><span
|
|---|
| 2159 | class="cmtt-8"> for</span><span
|
|---|
| 2160 | class="cmtt-8"> this</span><span
|
|---|
| 2161 | class="cmtt-8"> entry</span><span
|
|---|
| 2162 | class="cmtt-8"> is</span><span
|
|---|
| 2163 | class="cmtt-8"> [length]+1;</span><br class="fancyvrb" /><a
|
|---|
| 2164 | id="x1-51070r20"></a><span
|
|---|
| 2165 | class="cmr-6">20</span><br class="fancyvrb" /><a
|
|---|
| 2166 | id="x1-51072r21"></a><span
|
|---|
| 2167 | class="cmr-6">21</span><span
|
|---|
| 2168 | class="cmtt-8"> </span><span
|
|---|
| 2169 | class="cmtt-8"> </span><span
|
|---|
| 2170 | class="cmtt-8"> </span><span
|
|---|
| 2171 | class="cmtt-8"> </span><span
|
|---|
| 2172 | class="cmtt-8"> </span><span
|
|---|
| 2173 | class="cmsy-8">}</span><br class="fancyvrb" /><a
|
|---|
| 2174 | id="x1-51074r22"></a><span
|
|---|
| 2175 | class="cmr-6">22</span></div>
|
|---|
| 2176 |
|
|---|
| 2177 |
|
|---|
| 2178 |
|
|---|
| 2179 | </li>
|
|---|
| 2180 | <li class="itemize">If the <span
|
|---|
| 2181 | class="cmtt-12">[ordered] </span>flag is set, the codeword list for this codebook is encoded in
|
|---|
| 2182 | ascending length order. Rather than reading a length for every codeword, the
|
|---|
| 2183 | encoder reads the number of codewords per length. That is, beginning at entry
|
|---|
| 2184 | zero:
|
|---|
| 2185 | <!--l. 119--><p class="noindent" >
|
|---|
| 2186 | <div class="fancyvrb" id="fancyvrb12"><a
|
|---|
| 2187 | id="x1-51076r1"></a><span
|
|---|
| 2188 | class="cmr-6">1</span><span
|
|---|
| 2189 | class="cmtt-8"> </span><span
|
|---|
| 2190 | class="cmtt-8"> 1)</span><span
|
|---|
| 2191 | class="cmtt-8"> [current</span><span
|
|---|
| 2192 | class="cmtt-8">_entry]</span><span
|
|---|
| 2193 | class="cmtt-8"> =</span><span
|
|---|
| 2194 | class="cmtt-8"> 0;</span><br class="fancyvrb" /><a
|
|---|
| 2195 | id="x1-51078r2"></a><span
|
|---|
| 2196 | class="cmr-6">2</span><span
|
|---|
| 2197 | class="cmtt-8"> </span><span
|
|---|
| 2198 | class="cmtt-8"> 2)</span><span
|
|---|
| 2199 | class="cmtt-8"> [current</span><span
|
|---|
| 2200 | class="cmtt-8">_length]</span><span
|
|---|
| 2201 | class="cmtt-8"> =</span><span
|
|---|
| 2202 | class="cmtt-8"> read</span><span
|
|---|
| 2203 | class="cmtt-8"> a</span><span
|
|---|
| 2204 | class="cmtt-8"> five</span><span
|
|---|
| 2205 | class="cmtt-8"> bit</span><span
|
|---|
| 2206 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2207 | class="cmtt-8"> integer</span><span
|
|---|
| 2208 | class="cmtt-8"> and</span><span
|
|---|
| 2209 | class="cmtt-8"> add</span><span
|
|---|
| 2210 | class="cmtt-8"> 1;</span>
|
|---|
| 2211 | <br class="fancyvrb" /><a
|
|---|
| 2212 | id="x1-51080r3"></a><span
|
|---|
| 2213 | class="cmr-6">3</span><span
|
|---|
| 2214 | class="cmtt-8"> </span><span
|
|---|
| 2215 | class="cmtt-8"> 3)</span><span
|
|---|
| 2216 | class="cmtt-8"> [number]</span><span
|
|---|
| 2217 | class="cmtt-8"> =</span><span
|
|---|
| 2218 | class="cmtt-8"> read</span><span
|
|---|
| 2219 | class="cmtt-8"> </span><a
|
|---|
| 2220 | href="#x1-1190009.2.1"><span
|
|---|
| 2221 | class="cmtt-8">ilog</span></a><span
|
|---|
| 2222 | class="cmtt-8">([codebook</span><span
|
|---|
| 2223 | class="cmtt-8">_entries]</span><span
|
|---|
| 2224 | class="cmtt-8"> -</span><span
|
|---|
| 2225 | class="cmtt-8"> [current</span><span
|
|---|
| 2226 | class="cmtt-8">_entry])</span><span
|
|---|
| 2227 | class="cmtt-8"> bits</span><span
|
|---|
| 2228 | class="cmtt-8"> as</span><span
|
|---|
| 2229 | class="cmtt-8"> an</span><span
|
|---|
| 2230 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2231 | class="cmtt-8"> integer</span>
|
|---|
| 2232 | <br class="fancyvrb" /><a
|
|---|
| 2233 | id="x1-51082r4"></a><span
|
|---|
| 2234 | class="cmr-6">4</span><span
|
|---|
| 2235 | class="cmtt-8"> </span><span
|
|---|
| 2236 | class="cmtt-8"> 4)</span><span
|
|---|
| 2237 | class="cmtt-8"> set</span><span
|
|---|
| 2238 | class="cmtt-8"> the</span><span
|
|---|
| 2239 | class="cmtt-8"> entries</span><span
|
|---|
| 2240 | class="cmtt-8"> [current</span><span
|
|---|
| 2241 | class="cmtt-8">_entry]</span><span
|
|---|
| 2242 | class="cmtt-8"> through</span><span
|
|---|
| 2243 | class="cmtt-8"> [current</span><span
|
|---|
| 2244 | class="cmtt-8">_entry]+[number]-1,</span><span
|
|---|
| 2245 | class="cmtt-8"> inclusive,</span>
|
|---|
| 2246 | <br class="fancyvrb" /><a
|
|---|
| 2247 | id="x1-51084r5"></a><span
|
|---|
| 2248 | class="cmr-6">5</span><span
|
|---|
| 2249 | class="cmtt-8"> </span><span
|
|---|
| 2250 | class="cmtt-8"> </span><span
|
|---|
| 2251 | class="cmtt-8"> </span><span
|
|---|
| 2252 | class="cmtt-8"> of</span><span
|
|---|
| 2253 | class="cmtt-8"> the</span><span
|
|---|
| 2254 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2255 | class="cmtt-8">_codeword</span><span
|
|---|
| 2256 | class="cmtt-8">_lengths]</span><span
|
|---|
| 2257 | class="cmtt-8"> array</span><span
|
|---|
| 2258 | class="cmtt-8"> to</span><span
|
|---|
| 2259 | class="cmtt-8"> [current</span><span
|
|---|
| 2260 | class="cmtt-8">_length]</span><br class="fancyvrb" /><a
|
|---|
| 2261 | id="x1-51086r6"></a><span
|
|---|
| 2262 | class="cmr-6">6</span><span
|
|---|
| 2263 | class="cmtt-8"> </span><span
|
|---|
| 2264 | class="cmtt-8"> 5)</span><span
|
|---|
| 2265 | class="cmtt-8"> set</span><span
|
|---|
| 2266 | class="cmtt-8"> [current</span><span
|
|---|
| 2267 | class="cmtt-8">_entry]</span><span
|
|---|
| 2268 | class="cmtt-8"> to</span><span
|
|---|
| 2269 | class="cmtt-8"> [number]</span><span
|
|---|
| 2270 | class="cmtt-8"> +</span><span
|
|---|
| 2271 | class="cmtt-8"> [current</span><span
|
|---|
| 2272 | class="cmtt-8">_entry]</span>
|
|---|
| 2273 | <br class="fancyvrb" /><a
|
|---|
| 2274 | id="x1-51088r7"></a><span
|
|---|
| 2275 | class="cmr-6">7</span><span
|
|---|
| 2276 | class="cmtt-8"> </span><span
|
|---|
| 2277 | class="cmtt-8"> 6)</span><span
|
|---|
| 2278 | class="cmtt-8"> increment</span><span
|
|---|
| 2279 | class="cmtt-8"> [current</span><span
|
|---|
| 2280 | class="cmtt-8">_length]</span><span
|
|---|
| 2281 | class="cmtt-8"> by</span><span
|
|---|
| 2282 | class="cmtt-8"> 1</span><br class="fancyvrb" /><a
|
|---|
| 2283 | id="x1-51090r8"></a><span
|
|---|
| 2284 | class="cmr-6">8</span><span
|
|---|
| 2285 | class="cmtt-8"> </span><span
|
|---|
| 2286 | class="cmtt-8"> 7)</span><span
|
|---|
| 2287 | class="cmtt-8"> if</span><span
|
|---|
| 2288 | class="cmtt-8"> [current</span><span
|
|---|
| 2289 | class="cmtt-8">_entry]</span><span
|
|---|
| 2290 | class="cmtt-8"> is</span><span
|
|---|
| 2291 | class="cmtt-8"> greater</span><span
|
|---|
| 2292 | class="cmtt-8"> than</span><span
|
|---|
| 2293 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2294 | class="cmtt-8">_entries]</span><span
|
|---|
| 2295 | class="cmtt-8"> ERROR</span><span
|
|---|
| 2296 | class="cmtt-8"> CONDITION;</span>
|
|---|
| 2297 | <br class="fancyvrb" /><a
|
|---|
| 2298 | id="x1-51092r9"></a><span
|
|---|
| 2299 | class="cmr-6">9</span><span
|
|---|
| 2300 | class="cmtt-8"> </span><span
|
|---|
| 2301 | class="cmtt-8"> </span><span
|
|---|
| 2302 | class="cmtt-8"> </span><span
|
|---|
| 2303 | class="cmtt-8"> the</span><span
|
|---|
| 2304 | class="cmtt-8"> decoder</span><span
|
|---|
| 2305 | class="cmtt-8"> will</span><span
|
|---|
| 2306 | class="cmtt-8"> not</span><span
|
|---|
| 2307 | class="cmtt-8"> be</span><span
|
|---|
| 2308 | class="cmtt-8"> able</span><span
|
|---|
| 2309 | class="cmtt-8"> to</span><span
|
|---|
| 2310 | class="cmtt-8"> read</span><span
|
|---|
| 2311 | class="cmtt-8"> this</span><span
|
|---|
| 2312 | class="cmtt-8"> stream.</span><br class="fancyvrb" /><a
|
|---|
| 2313 | id="x1-51094r10"></a><span
|
|---|
| 2314 | class="cmr-6">10</span><span
|
|---|
| 2315 | class="cmtt-8"> </span><span
|
|---|
| 2316 | class="cmtt-8"> 8)</span><span
|
|---|
| 2317 | class="cmtt-8"> if</span><span
|
|---|
| 2318 | class="cmtt-8"> [current</span><span
|
|---|
| 2319 | class="cmtt-8">_entry]</span><span
|
|---|
| 2320 | class="cmtt-8"> is</span><span
|
|---|
| 2321 | class="cmtt-8"> less</span><span
|
|---|
| 2322 | class="cmtt-8"> than</span><span
|
|---|
| 2323 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2324 | class="cmtt-8">_entries],</span><span
|
|---|
| 2325 | class="cmtt-8"> repeat</span><span
|
|---|
| 2326 | class="cmtt-8"> process</span><span
|
|---|
| 2327 | class="cmtt-8"> starting</span><span
|
|---|
| 2328 | class="cmtt-8"> at</span><span
|
|---|
| 2329 | class="cmtt-8"> 3)</span>
|
|---|
| 2330 | <br class="fancyvrb" /><a
|
|---|
| 2331 | id="x1-51096r11"></a><span
|
|---|
| 2332 | class="cmr-6">11</span><span
|
|---|
| 2333 | class="cmtt-8"> </span><span
|
|---|
| 2334 | class="cmtt-8"> 9)</span><span
|
|---|
| 2335 | class="cmtt-8"> done.</span></div>
|
|---|
| 2336 | </li></ul>
|
|---|
| 2337 | <!--l. 135--><p class="noindent" >After all codeword lengths have been decoded, the decoder reads the vector lookup table. Vorbis
|
|---|
| 2338 | I supports three lookup types:
|
|---|
| 2339 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 2340 | 1. </dt><dd
|
|---|
| 2341 | class="enumerate-enumitem">No lookup
|
|---|
| 2342 | </dd><dt class="enumerate-enumitem">
|
|---|
| 2343 | 2. </dt><dd
|
|---|
| 2344 | class="enumerate-enumitem">Implicitly populated value mapping (lattice VQ)
|
|---|
| 2345 | </dd><dt class="enumerate-enumitem">
|
|---|
| 2346 | 3. </dt><dd
|
|---|
| 2347 | class="enumerate-enumitem">Explicitly populated value mapping (tessellated or ’foam’ VQ)</dd></dl>
|
|---|
| 2348 | <!--l. 148--><p class="noindent" >The lookup table type is read as a four bit unsigned integer:
|
|---|
| 2349 | <div class="fancyvrb" id="fancyvrb13"><a
|
|---|
| 2350 | id="x1-51101r1"></a><span
|
|---|
| 2351 | class="cmr-6">1</span><span
|
|---|
| 2352 | class="cmtt-8"> </span><span
|
|---|
| 2353 | class="cmtt-8"> 1)</span><span
|
|---|
| 2354 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2355 | class="cmtt-8">_lookup</span><span
|
|---|
| 2356 | class="cmtt-8">_type]</span><span
|
|---|
| 2357 | class="cmtt-8"> =</span><span
|
|---|
| 2358 | class="cmtt-8"> read</span><span
|
|---|
| 2359 | class="cmtt-8"> four</span><span
|
|---|
| 2360 | class="cmtt-8"> bits</span><span
|
|---|
| 2361 | class="cmtt-8"> as</span><span
|
|---|
| 2362 | class="cmtt-8"> an</span><span
|
|---|
| 2363 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2364 | class="cmtt-8"> integer</span></div>
|
|---|
| 2365 | <!--l. 153--><p class="noindent" >Codebook decode precedes according to <span
|
|---|
| 2366 | class="cmtt-12">[codebook</span><span
|
|---|
| 2367 | class="cmtt-12">_lookup</span><span
|
|---|
| 2368 | class="cmtt-12">_type]</span>:
|
|---|
| 2369 | <ul class="itemize1">
|
|---|
| 2370 | <li class="itemize">Lookup type zero indicates no lookup to be read. Proceed past lookup decode.
|
|---|
| 2371 | </li>
|
|---|
| 2372 | <li class="itemize">Lookup types one and two are similar, differing only in the number of lookup values to
|
|---|
| 2373 | be read. Lookup type one reads a list of values that are permuted in a set pattern to
|
|---|
| 2374 | build a list of vectors, each vector of order <span
|
|---|
| 2375 | class="cmtt-12">[codebook</span><span
|
|---|
| 2376 | class="cmtt-12">_dimensions] </span>scalars. Lookup
|
|---|
| 2377 | type two builds the same vector list, but reads each scalar for each vector explicitly,
|
|---|
| 2378 | rather than building vectors from a smaller list of possible scalar values. Lookup
|
|---|
| 2379 | decode proceeds as follows:
|
|---|
| 2380 | <!--l. 167--><p class="noindent" >
|
|---|
| 2381 | <div class="fancyvrb" id="fancyvrb14"><a
|
|---|
| 2382 | id="x1-51103r1"></a><span
|
|---|
| 2383 | class="cmr-6">1</span><span
|
|---|
| 2384 | class="cmtt-8"> </span><span
|
|---|
| 2385 | class="cmtt-8"> 1)</span><span
|
|---|
| 2386 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2387 | class="cmtt-8">_minimum</span><span
|
|---|
| 2388 | class="cmtt-8">_value]</span><span
|
|---|
| 2389 | class="cmtt-8"> =</span><span
|
|---|
| 2390 | class="cmtt-8"> </span><a
|
|---|
| 2391 | href="#x1-1200009.2.2"><span
|
|---|
| 2392 | class="cmtt-8">float32</span><span
|
|---|
| 2393 | class="cmtt-8">_unpack</span></a><span
|
|---|
| 2394 | class="cmtt-8">(</span><span
|
|---|
| 2395 | class="cmtt-8"> read</span><span
|
|---|
| 2396 | class="cmtt-8"> 32</span><span
|
|---|
| 2397 | class="cmtt-8"> bits</span><span
|
|---|
| 2398 | class="cmtt-8"> as</span><span
|
|---|
| 2399 | class="cmtt-8"> an</span><span
|
|---|
| 2400 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2401 | class="cmtt-8"> integer)</span>
|
|---|
| 2402 | <br class="fancyvrb" /><a
|
|---|
| 2403 | id="x1-51105r2"></a><span
|
|---|
| 2404 | class="cmr-6">2</span><span
|
|---|
| 2405 | class="cmtt-8"> </span><span
|
|---|
| 2406 | class="cmtt-8"> 2)</span><span
|
|---|
| 2407 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2408 | class="cmtt-8">_delta</span><span
|
|---|
| 2409 | class="cmtt-8">_value]</span><span
|
|---|
| 2410 | class="cmtt-8"> =</span><span
|
|---|
| 2411 | class="cmtt-8"> </span><a
|
|---|
| 2412 | href="#x1-1200009.2.2"><span
|
|---|
| 2413 | class="cmtt-8">float32</span><span
|
|---|
| 2414 | class="cmtt-8">_unpack</span></a><span
|
|---|
| 2415 | class="cmtt-8">(</span><span
|
|---|
| 2416 | class="cmtt-8"> read</span><span
|
|---|
| 2417 | class="cmtt-8"> 32</span><span
|
|---|
| 2418 | class="cmtt-8"> bits</span><span
|
|---|
| 2419 | class="cmtt-8"> as</span><span
|
|---|
| 2420 | class="cmtt-8"> an</span><span
|
|---|
| 2421 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2422 | class="cmtt-8"> integer)</span>
|
|---|
| 2423 | <br class="fancyvrb" /><a
|
|---|
| 2424 | id="x1-51107r3"></a><span
|
|---|
| 2425 | class="cmr-6">3</span><span
|
|---|
| 2426 | class="cmtt-8"> </span><span
|
|---|
| 2427 | class="cmtt-8"> 3)</span><span
|
|---|
| 2428 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2429 | class="cmtt-8">_value</span><span
|
|---|
| 2430 | class="cmtt-8">_bits]</span><span
|
|---|
| 2431 | class="cmtt-8"> =</span><span
|
|---|
| 2432 | class="cmtt-8"> read</span><span
|
|---|
| 2433 | class="cmtt-8"> 4</span><span
|
|---|
| 2434 | class="cmtt-8"> bits</span><span
|
|---|
| 2435 | class="cmtt-8"> as</span><span
|
|---|
| 2436 | class="cmtt-8"> an</span><span
|
|---|
| 2437 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2438 | class="cmtt-8"> integer</span><span
|
|---|
| 2439 | class="cmtt-8"> and</span><span
|
|---|
| 2440 | class="cmtt-8"> add</span><span
|
|---|
| 2441 | class="cmtt-8"> 1</span><br class="fancyvrb" /><a
|
|---|
| 2442 | id="x1-51109r4"></a><span
|
|---|
| 2443 | class="cmr-6">4</span><span
|
|---|
| 2444 | class="cmtt-8"> </span><span
|
|---|
| 2445 | class="cmtt-8"> 4)</span><span
|
|---|
| 2446 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2447 | class="cmtt-8">_sequence</span><span
|
|---|
| 2448 | class="cmtt-8">_p]</span><span
|
|---|
| 2449 | class="cmtt-8"> =</span><span
|
|---|
| 2450 | class="cmtt-8"> read</span><span
|
|---|
| 2451 | class="cmtt-8"> 1</span><span
|
|---|
| 2452 | class="cmtt-8"> bit</span><span
|
|---|
| 2453 | class="cmtt-8"> as</span><span
|
|---|
| 2454 | class="cmtt-8"> a</span><span
|
|---|
| 2455 | class="cmtt-8"> boolean</span><span
|
|---|
| 2456 | class="cmtt-8"> flag</span><br class="fancyvrb" /><a
|
|---|
| 2457 | id="x1-51111r5"></a><span
|
|---|
| 2458 | class="cmr-6">5</span>
|
|---|
| 2459 |
|
|---|
| 2460 |
|
|---|
| 2461 |
|
|---|
| 2462 | <br class="fancyvrb" /><a
|
|---|
| 2463 | id="x1-51113r6"></a><span
|
|---|
| 2464 | class="cmr-6">6</span><span
|
|---|
| 2465 | class="cmtt-8"> </span><span
|
|---|
| 2466 | class="cmtt-8"> if</span><span
|
|---|
| 2467 | class="cmtt-8"> (</span><span
|
|---|
| 2468 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2469 | class="cmtt-8">_lookup</span><span
|
|---|
| 2470 | class="cmtt-8">_type]</span><span
|
|---|
| 2471 | class="cmtt-8"> is</span><span
|
|---|
| 2472 | class="cmtt-8"> 1</span><span
|
|---|
| 2473 | class="cmtt-8"> )</span><span
|
|---|
| 2474 | class="cmtt-8"> </span><span
|
|---|
| 2475 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 2476 | id="x1-51115r7"></a><span
|
|---|
| 2477 | class="cmr-6">7</span><br class="fancyvrb" /><a
|
|---|
| 2478 | id="x1-51117r8"></a><span
|
|---|
| 2479 | class="cmr-6">8</span><span
|
|---|
| 2480 | class="cmtt-8"> </span><span
|
|---|
| 2481 | class="cmtt-8"> </span><span
|
|---|
| 2482 | class="cmtt-8"> </span><span
|
|---|
| 2483 | class="cmtt-8"> </span><span
|
|---|
| 2484 | class="cmtt-8"> 5)</span><span
|
|---|
| 2485 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2486 | class="cmtt-8">_lookup</span><span
|
|---|
| 2487 | class="cmtt-8">_values]</span><span
|
|---|
| 2488 | class="cmtt-8"> =</span><span
|
|---|
| 2489 | class="cmtt-8"> </span><a
|
|---|
| 2490 | href="#x1-1210009.2.3"><span
|
|---|
| 2491 | class="cmtt-8">lookup1</span><span
|
|---|
| 2492 | class="cmtt-8">_values</span></a><span
|
|---|
| 2493 | class="cmtt-8">([codebook</span><span
|
|---|
| 2494 | class="cmtt-8">_entries],</span><span
|
|---|
| 2495 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2496 | class="cmtt-8">_dimensions]</span><span
|
|---|
| 2497 | class="cmtt-8"> )</span><br class="fancyvrb" /><a
|
|---|
| 2498 | id="x1-51119r9"></a><span
|
|---|
| 2499 | class="cmr-6">9</span>
|
|---|
| 2500 | <br class="fancyvrb" /><a
|
|---|
| 2501 | id="x1-51121r10"></a><span
|
|---|
| 2502 | class="cmr-6">10</span><span
|
|---|
| 2503 | class="cmtt-8"> </span><span
|
|---|
| 2504 | class="cmtt-8"> </span><span
|
|---|
| 2505 | class="cmsy-8">}</span><span
|
|---|
| 2506 | class="cmtt-8"> else</span><span
|
|---|
| 2507 | class="cmtt-8"> </span><span
|
|---|
| 2508 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 2509 | id="x1-51123r11"></a><span
|
|---|
| 2510 | class="cmr-6">11</span><br class="fancyvrb" /><a
|
|---|
| 2511 | id="x1-51125r12"></a><span
|
|---|
| 2512 | class="cmr-6">12</span><span
|
|---|
| 2513 | class="cmtt-8"> </span><span
|
|---|
| 2514 | class="cmtt-8"> </span><span
|
|---|
| 2515 | class="cmtt-8"> </span><span
|
|---|
| 2516 | class="cmtt-8"> </span><span
|
|---|
| 2517 | class="cmtt-8"> 6)</span><span
|
|---|
| 2518 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2519 | class="cmtt-8">_lookup</span><span
|
|---|
| 2520 | class="cmtt-8">_values]</span><span
|
|---|
| 2521 | class="cmtt-8"> =</span><span
|
|---|
| 2522 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2523 | class="cmtt-8">_entries]</span><span
|
|---|
| 2524 | class="cmtt-8"> *</span><span
|
|---|
| 2525 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2526 | class="cmtt-8">_dimensions]</span><br class="fancyvrb" /><a
|
|---|
| 2527 | id="x1-51127r13"></a><span
|
|---|
| 2528 | class="cmr-6">13</span><br class="fancyvrb" /><a
|
|---|
| 2529 | id="x1-51129r14"></a><span
|
|---|
| 2530 | class="cmr-6">14</span><span
|
|---|
| 2531 | class="cmtt-8"> </span><span
|
|---|
| 2532 | class="cmtt-8"> </span><span
|
|---|
| 2533 | class="cmsy-8">}</span><br class="fancyvrb" /><a
|
|---|
| 2534 | id="x1-51131r15"></a><span
|
|---|
| 2535 | class="cmr-6">15</span>
|
|---|
| 2536 | <br class="fancyvrb" /><a
|
|---|
| 2537 | id="x1-51133r16"></a><span
|
|---|
| 2538 | class="cmr-6">16</span><span
|
|---|
| 2539 | class="cmtt-8"> </span><span
|
|---|
| 2540 | class="cmtt-8"> 7)</span><span
|
|---|
| 2541 | class="cmtt-8"> read</span><span
|
|---|
| 2542 | class="cmtt-8"> a</span><span
|
|---|
| 2543 | class="cmtt-8"> total</span><span
|
|---|
| 2544 | class="cmtt-8"> of</span><span
|
|---|
| 2545 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2546 | class="cmtt-8">_lookup</span><span
|
|---|
| 2547 | class="cmtt-8">_values]</span><span
|
|---|
| 2548 | class="cmtt-8"> unsigned</span><span
|
|---|
| 2549 | class="cmtt-8"> integers</span><span
|
|---|
| 2550 | class="cmtt-8"> of</span><span
|
|---|
| 2551 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2552 | class="cmtt-8">_value</span><span
|
|---|
| 2553 | class="cmtt-8">_bits]</span><span
|
|---|
| 2554 | class="cmtt-8"> each;</span>
|
|---|
| 2555 | <br class="fancyvrb" /><a
|
|---|
| 2556 | id="x1-51135r17"></a><span
|
|---|
| 2557 | class="cmr-6">17</span><span
|
|---|
| 2558 | class="cmtt-8"> </span><span
|
|---|
| 2559 | class="cmtt-8"> </span><span
|
|---|
| 2560 | class="cmtt-8"> </span><span
|
|---|
| 2561 | class="cmtt-8"> </span><span
|
|---|
| 2562 | class="cmtt-8"> store</span><span
|
|---|
| 2563 | class="cmtt-8"> these</span><span
|
|---|
| 2564 | class="cmtt-8"> in</span><span
|
|---|
| 2565 | class="cmtt-8"> order</span><span
|
|---|
| 2566 | class="cmtt-8"> in</span><span
|
|---|
| 2567 | class="cmtt-8"> the</span><span
|
|---|
| 2568 | class="cmtt-8"> array</span><span
|
|---|
| 2569 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2570 | class="cmtt-8">_multiplicands]</span></div>
|
|---|
| 2571 | </li>
|
|---|
| 2572 | <li class="itemize">A <span
|
|---|
| 2573 | class="cmtt-12">[codebook</span><span
|
|---|
| 2574 | class="cmtt-12">_lookup</span><span
|
|---|
| 2575 | class="cmtt-12">_type] </span>of greater than two is reserved and indicates a stream that is
|
|---|
| 2576 | not decodable by the specification in this document.
|
|---|
| 2577 | </li></ul>
|
|---|
| 2578 | <!--l. 194--><p class="noindent" >An ’end of packet’ during any read operation in the above steps is considered an error condition
|
|---|
| 2579 | rendering the stream undecodable.
|
|---|
| 2580 | <!--l. 197--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 2581 | id="x1-520003.2.1"></a><span
|
|---|
| 2582 | class="cmbx-12">Huffman decision tree representation</span></span>
|
|---|
| 2583 | The <span
|
|---|
| 2584 | class="cmtt-12">[codebook</span><span
|
|---|
| 2585 | class="cmtt-12">_codeword</span><span
|
|---|
| 2586 | class="cmtt-12">_lengths] </span>array and <span
|
|---|
| 2587 | class="cmtt-12">[codebook</span><span
|
|---|
| 2588 | class="cmtt-12">_entries] </span>value uniquely define the
|
|---|
| 2589 | Huffman decision tree used for entropy decoding.
|
|---|
| 2590 | <!--l. 203--><p class="noindent" >Briefly, each used codebook entry (recall that length-unordered codebooks support unused
|
|---|
| 2591 | codeword entries) is assigned, in order, the lowest valued unused binary Huffman codeword
|
|---|
| 2592 | possible. Assume the following codeword length list:
|
|---|
| 2593 | <!--l. 208--><p class="noindent" >
|
|---|
| 2594 | <div class="fancyvrb" id="fancyvrb15"><a
|
|---|
| 2595 | id="x1-52002r1"></a><span
|
|---|
| 2596 | class="cmr-6">1</span><span
|
|---|
| 2597 | class="cmtt-8">entry</span><span
|
|---|
| 2598 | class="cmtt-8"> 0:</span><span
|
|---|
| 2599 | class="cmtt-8"> length</span><span
|
|---|
| 2600 | class="cmtt-8"> 2</span><br class="fancyvrb" /><a
|
|---|
| 2601 | id="x1-52004r2"></a><span
|
|---|
| 2602 | class="cmr-6">2</span><span
|
|---|
| 2603 | class="cmtt-8">entry</span><span
|
|---|
| 2604 | class="cmtt-8"> 1:</span><span
|
|---|
| 2605 | class="cmtt-8"> length</span><span
|
|---|
| 2606 | class="cmtt-8"> 4</span><br class="fancyvrb" /><a
|
|---|
| 2607 | id="x1-52006r3"></a><span
|
|---|
| 2608 | class="cmr-6">3</span><span
|
|---|
| 2609 | class="cmtt-8">entry</span><span
|
|---|
| 2610 | class="cmtt-8"> 2:</span><span
|
|---|
| 2611 | class="cmtt-8"> length</span><span
|
|---|
| 2612 | class="cmtt-8"> 4</span><br class="fancyvrb" /><a
|
|---|
| 2613 | id="x1-52008r4"></a><span
|
|---|
| 2614 | class="cmr-6">4</span><span
|
|---|
| 2615 | class="cmtt-8">entry</span><span
|
|---|
| 2616 | class="cmtt-8"> 3:</span><span
|
|---|
| 2617 | class="cmtt-8"> length</span><span
|
|---|
| 2618 | class="cmtt-8"> 4</span><br class="fancyvrb" /><a
|
|---|
| 2619 | id="x1-52010r5"></a><span
|
|---|
| 2620 | class="cmr-6">5</span><span
|
|---|
| 2621 | class="cmtt-8">entry</span><span
|
|---|
| 2622 | class="cmtt-8"> 4:</span><span
|
|---|
| 2623 | class="cmtt-8"> length</span><span
|
|---|
| 2624 | class="cmtt-8"> 4</span><br class="fancyvrb" /><a
|
|---|
| 2625 | id="x1-52012r6"></a><span
|
|---|
| 2626 | class="cmr-6">6</span><span
|
|---|
| 2627 | class="cmtt-8">entry</span><span
|
|---|
| 2628 | class="cmtt-8"> 5:</span><span
|
|---|
| 2629 | class="cmtt-8"> length</span><span
|
|---|
| 2630 | class="cmtt-8"> 2</span><br class="fancyvrb" /><a
|
|---|
| 2631 | id="x1-52014r7"></a><span
|
|---|
| 2632 | class="cmr-6">7</span><span
|
|---|
| 2633 | class="cmtt-8">entry</span><span
|
|---|
| 2634 | class="cmtt-8"> 6:</span><span
|
|---|
| 2635 | class="cmtt-8"> length</span><span
|
|---|
| 2636 | class="cmtt-8"> 3</span><br class="fancyvrb" /><a
|
|---|
| 2637 | id="x1-52016r8"></a><span
|
|---|
| 2638 | class="cmr-6">8</span><span
|
|---|
| 2639 | class="cmtt-8">entry</span><span
|
|---|
| 2640 | class="cmtt-8"> 7:</span><span
|
|---|
| 2641 | class="cmtt-8"> length</span><span
|
|---|
| 2642 | class="cmtt-8"> 3</span></div>
|
|---|
| 2643 | <!--l. 219--><p class="noindent" >Assigning codewords in order (lowest possible value of the appropriate length to highest) results
|
|---|
| 2644 | in the following codeword list:
|
|---|
| 2645 | <!--l. 222--><p class="noindent" >
|
|---|
| 2646 | <div class="fancyvrb" id="fancyvrb16"><a
|
|---|
| 2647 | id="x1-52018r1"></a><span
|
|---|
| 2648 | class="cmr-6">1</span><span
|
|---|
| 2649 | class="cmtt-8">entry</span><span
|
|---|
| 2650 | class="cmtt-8"> 0:</span><span
|
|---|
| 2651 | class="cmtt-8"> length</span><span
|
|---|
| 2652 | class="cmtt-8"> 2</span><span
|
|---|
| 2653 | class="cmtt-8"> codeword</span><span
|
|---|
| 2654 | class="cmtt-8"> 00</span><br class="fancyvrb" /><a
|
|---|
| 2655 | id="x1-52020r2"></a><span
|
|---|
| 2656 | class="cmr-6">2</span><span
|
|---|
| 2657 | class="cmtt-8">entry</span><span
|
|---|
| 2658 | class="cmtt-8"> 1:</span><span
|
|---|
| 2659 | class="cmtt-8"> length</span><span
|
|---|
| 2660 | class="cmtt-8"> 4</span><span
|
|---|
| 2661 | class="cmtt-8"> codeword</span><span
|
|---|
| 2662 | class="cmtt-8"> 0100</span><br class="fancyvrb" /><a
|
|---|
| 2663 | id="x1-52022r3"></a><span
|
|---|
| 2664 | class="cmr-6">3</span><span
|
|---|
| 2665 | class="cmtt-8">entry</span><span
|
|---|
| 2666 | class="cmtt-8"> 2:</span><span
|
|---|
| 2667 | class="cmtt-8"> length</span><span
|
|---|
| 2668 | class="cmtt-8"> 4</span><span
|
|---|
| 2669 | class="cmtt-8"> codeword</span><span
|
|---|
| 2670 | class="cmtt-8"> 0101</span><br class="fancyvrb" /><a
|
|---|
| 2671 | id="x1-52024r4"></a><span
|
|---|
| 2672 | class="cmr-6">4</span><span
|
|---|
| 2673 | class="cmtt-8">entry</span><span
|
|---|
| 2674 | class="cmtt-8"> 3:</span><span
|
|---|
| 2675 | class="cmtt-8"> length</span><span
|
|---|
| 2676 | class="cmtt-8"> 4</span><span
|
|---|
| 2677 | class="cmtt-8"> codeword</span><span
|
|---|
| 2678 | class="cmtt-8"> 0110</span>
|
|---|
| 2679 | <br class="fancyvrb" /><a
|
|---|
| 2680 | id="x1-52026r5"></a><span
|
|---|
| 2681 | class="cmr-6">5</span><span
|
|---|
| 2682 | class="cmtt-8">entry</span><span
|
|---|
| 2683 | class="cmtt-8"> 4:</span><span
|
|---|
| 2684 | class="cmtt-8"> length</span><span
|
|---|
| 2685 | class="cmtt-8"> 4</span><span
|
|---|
| 2686 | class="cmtt-8"> codeword</span><span
|
|---|
| 2687 | class="cmtt-8"> 0111</span><br class="fancyvrb" /><a
|
|---|
| 2688 | id="x1-52028r6"></a><span
|
|---|
| 2689 | class="cmr-6">6</span><span
|
|---|
| 2690 | class="cmtt-8">entry</span><span
|
|---|
| 2691 | class="cmtt-8"> 5:</span><span
|
|---|
| 2692 | class="cmtt-8"> length</span><span
|
|---|
| 2693 | class="cmtt-8"> 2</span><span
|
|---|
| 2694 | class="cmtt-8"> codeword</span><span
|
|---|
| 2695 | class="cmtt-8"> 10</span><br class="fancyvrb" /><a
|
|---|
| 2696 | id="x1-52030r7"></a><span
|
|---|
| 2697 | class="cmr-6">7</span><span
|
|---|
| 2698 | class="cmtt-8">entry</span><span
|
|---|
| 2699 | class="cmtt-8"> 6:</span><span
|
|---|
| 2700 | class="cmtt-8"> length</span><span
|
|---|
| 2701 | class="cmtt-8"> 3</span><span
|
|---|
| 2702 | class="cmtt-8"> codeword</span><span
|
|---|
| 2703 | class="cmtt-8"> 110</span><br class="fancyvrb" /><a
|
|---|
| 2704 | id="x1-52032r8"></a><span
|
|---|
| 2705 | class="cmr-6">8</span><span
|
|---|
| 2706 | class="cmtt-8">entry</span><span
|
|---|
| 2707 | class="cmtt-8"> 7:</span><span
|
|---|
| 2708 | class="cmtt-8"> length</span><span
|
|---|
| 2709 | class="cmtt-8"> 3</span><span
|
|---|
| 2710 | class="cmtt-8"> codeword</span><span
|
|---|
| 2711 | class="cmtt-8"> 111</span></div>
|
|---|
| 2712 | <!--l. 234--><p class="noindent" ><span class="likesubparagraphHead"><a
|
|---|
| 2713 | id="x1-530003.2.1"></a><span
|
|---|
| 2714 | class="cmbx-12">Note:</span></span> Unlike most binary numerical values in this document, we intend the above codewords to
|
|---|
| 2715 | be read and used bit by bit from left to right, thus the codeword ’001’ is the bit string ’zero, zero,
|
|---|
| 2716 | one’. When determining ’lowest possible value’ in the assignment definition above, the leftmost
|
|---|
| 2717 | bit is the MSb.
|
|---|
| 2718 | <!--l. 242--><p class="noindent" >It is clear that the codeword length list represents a Huffman decision tree with the entry
|
|---|
| 2719 | numbers equivalent to the leaves numbered left-to-right:
|
|---|
| 2720 |
|
|---|
| 2721 |
|
|---|
| 2722 |
|
|---|
| 2723 | <div class="center"
|
|---|
| 2724 | >
|
|---|
| 2725 | <!--l. 246--><p class="noindent" >
|
|---|
| 2726 |
|
|---|
| 2727 | <!--l. 247--><p class="noindent" ><img
|
|---|
| 2728 | src="hufftree.png" alt="PIC"
|
|---|
| 2729 | >
|
|---|
| 2730 | <br /> <div class="caption"
|
|---|
| 2731 | ><span class="id">Figure 4: </span><span
|
|---|
| 2732 | class="content">huffman tree illustration</span></div><!--tex4ht:label?: x1-530014 -->
|
|---|
| 2733 | </div>
|
|---|
| 2734 | <!--l. 252--><p class="noindent" >As we assign codewords in order, we see that each choice constructs a new leaf in the leftmost
|
|---|
| 2735 | possible position.
|
|---|
| 2736 | <!--l. 255--><p class="noindent" >Note that it’s possible to underspecify or overspecify a Huffman tree via the length list.
|
|---|
| 2737 | In the above example, if codeword seven were eliminated, it’s clear that the tree is
|
|---|
| 2738 | unfinished:
|
|---|
| 2739 | <div class="center"
|
|---|
| 2740 | >
|
|---|
| 2741 | <!--l. 259--><p class="noindent" >
|
|---|
| 2742 |
|
|---|
| 2743 | <!--l. 260--><p class="noindent" ><img
|
|---|
| 2744 | src="hufftree-under.png" alt="PIC"
|
|---|
| 2745 | >
|
|---|
| 2746 | <br /> <div class="caption"
|
|---|
| 2747 | ><span class="id">Figure 5: </span><span
|
|---|
| 2748 | class="content">underspecified huffman tree illustration</span></div><!--tex4ht:label?: x1-530025 -->
|
|---|
| 2749 | </div>
|
|---|
| 2750 | <!--l. 265--><p class="noindent" >Similarly, in the original codebook, it’s clear that the tree is fully populated and a ninth
|
|---|
| 2751 | codeword is impossible. Both underspecified and overspecified trees are an error condition
|
|---|
| 2752 | rendering the stream undecodable.
|
|---|
| 2753 | <!--l. 270--><p class="noindent" >Codebook entries marked ’unused’ are simply skipped in the assigning process. They have no
|
|---|
| 2754 | codeword and do not appear in the decision tree, thus it’s impossible for any bit pattern read
|
|---|
| 2755 | from the stream to decode to that entry number.
|
|---|
| 2756 | <!--l. 275--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 2757 | id="x1-540003.2.1"></a><span
|
|---|
| 2758 | class="cmbx-12">Errata 20150226: Single entry codebooks</span></span>
|
|---|
| 2759 | A ’single-entry codebook’ is a codebook with one active codeword entry. A single-entry codebook
|
|---|
| 2760 | may be either a fully populated codebook with only one declared entry, or a sparse codebook
|
|---|
| 2761 | with only one entry marked used. The Vorbis I spec provides no means to specify a codeword
|
|---|
| 2762 | length of zero, and as a result, a single-entry codebook is inherently malformed because it is
|
|---|
| 2763 | underpopulated. The original specification did not address directly the matter of single-entry
|
|---|
| 2764 | codebooks; they were implicitly illegal as it was not possible to write such a codebook with a
|
|---|
| 2765 | valid tree structure.
|
|---|
| 2766 |
|
|---|
| 2767 |
|
|---|
| 2768 |
|
|---|
| 2769 | <!--l. 287--><p class="noindent" >In r14811 of the libvorbis reference implementation, Xiph added an additional check to the
|
|---|
| 2770 | codebook implementation to reject underpopulated Huffman trees. This change led to the
|
|---|
| 2771 | discovery of single-entry books used ’in the wild’ when the new, stricter checks rejected a number
|
|---|
| 2772 | of apparently working streams.
|
|---|
| 2773 | <!--l. 293--><p class="noindent" >In order to minimize breakage of deployed (if technically erroneous) streams, r16073 of the
|
|---|
| 2774 | reference implementation explicitly special-cased single-entry codebooks to tolerate the
|
|---|
| 2775 | single-entry case. Commit r16073 also added the following to the specification:
|
|---|
| 2776 | <!--l. 302--><p class="noindent" >“<span class="sout">Take special care that a codebook with a single used entry is handled properly; it consists of a
|
|---|
| 2777 | single codework of zero bits and reading a value out of such a codebook always returns the single
|
|---|
| 2778 | used value and sinks zero bits. </span>”
|
|---|
| 2779 | <!--l. 304--><p class="noindent" >The intent was to clarify the spec and codify current practice. However, this addition is
|
|---|
| 2780 | erroneously at odds with the intent of preserving usability of existing streams using single-entry
|
|---|
| 2781 | codebooks, disagrees with the code changes that reinstated decoding, and does not address how
|
|---|
| 2782 | single-entry codebooks should be encoded.
|
|---|
| 2783 | <!--l. 310--><p class="noindent" >As such, the above addition made in r16037 is struck from the specification and replaced by the
|
|---|
| 2784 | following:
|
|---|
| 2785 | <!--l. 329--><p class="noindent" >
|
|---|
| 2786 | <div class="quote">
|
|---|
| 2787 | <!--l. 329--><p class="noindent" >It is possible to declare a Vorbis codebook containing a single codework
|
|---|
| 2788 | entry. A single-entry codebook may be either a fully populated codebook with
|
|---|
| 2789 | <span
|
|---|
| 2790 | class="cmtt-12">[codebook</span><span
|
|---|
| 2791 | class="cmtt-12">_entries] </span>set to 1, or a sparse codebook marking only one entry
|
|---|
| 2792 | used. Note that it is not possible to also encode a <span
|
|---|
| 2793 | class="cmtt-12">[codeword</span><span
|
|---|
| 2794 | class="cmtt-12">_length] </span>of zero
|
|---|
| 2795 | for the single used codeword, as the unsigned value written to the stream
|
|---|
| 2796 | is <span
|
|---|
| 2797 | class="cmtt-12">[codeword</span><span
|
|---|
| 2798 | class="cmtt-12">_length]-1</span>. Instead, encoder implementations should indicate a
|
|---|
| 2799 | <span
|
|---|
| 2800 | class="cmtt-12">[codeword</span><span
|
|---|
| 2801 | class="cmtt-12">_length] </span>of 1 and ’write’ the codeword to a stream during audio
|
|---|
| 2802 | encoding by writing a single zero bit.
|
|---|
| 2803 | <!--l. 329--><p class="noindent" >Decoder implementations shall reject a codebook if it contains only one used
|
|---|
| 2804 | entry and the encoded <span
|
|---|
| 2805 | class="cmtt-12">[codeword</span><span
|
|---|
| 2806 | class="cmtt-12">_length] </span>of that entry is not 1. ’Reading’ a
|
|---|
| 2807 | value from single-entry codebook always returns the single used codeword value
|
|---|
| 2808 | and sinks one bit. Decoders should tolerate that the bit read from the stream
|
|---|
| 2809 | be ’1’ instead of ’0’; both values shall return the single used codeword.</div>
|
|---|
| 2810 | <!--l. 331--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 2811 | id="x1-550003.2.1"></a><span
|
|---|
| 2812 | class="cmbx-12">VQ lookup table vector representation</span></span>
|
|---|
| 2813 | Unpacking the VQ lookup table vectors relies on the following values:
|
|---|
| 2814 |
|
|---|
| 2815 |
|
|---|
| 2816 |
|
|---|
| 2817 | <div class="fancyvrb" id="fancyvrb17"><a
|
|---|
| 2818 | id="x1-55002r1"></a><span
|
|---|
| 2819 | class="cmr-6">1</span><span
|
|---|
| 2820 | class="cmtt-8">the</span><span
|
|---|
| 2821 | class="cmtt-8"> [codebook\_multiplicands]</span><span
|
|---|
| 2822 | class="cmtt-8"> array</span><br class="fancyvrb" /><a
|
|---|
| 2823 | id="x1-55004r2"></a><span
|
|---|
| 2824 | class="cmr-6">2</span><span
|
|---|
| 2825 | class="cmtt-8">[codebook\_minimum\_value]</span><br class="fancyvrb" /><a
|
|---|
| 2826 | id="x1-55006r3"></a><span
|
|---|
| 2827 | class="cmr-6">3</span><span
|
|---|
| 2828 | class="cmtt-8">[codebook\_delta\_value]</span><br class="fancyvrb" /><a
|
|---|
| 2829 | id="x1-55008r4"></a><span
|
|---|
| 2830 | class="cmr-6">4</span><span
|
|---|
| 2831 | class="cmtt-8">[codebook\_sequence\_p]</span>
|
|---|
| 2832 | <br class="fancyvrb" /><a
|
|---|
| 2833 | id="x1-55010r5"></a><span
|
|---|
| 2834 | class="cmr-6">5</span><span
|
|---|
| 2835 | class="cmtt-8">[codebook\_lookup\_type]</span><br class="fancyvrb" /><a
|
|---|
| 2836 | id="x1-55012r6"></a><span
|
|---|
| 2837 | class="cmr-6">6</span><span
|
|---|
| 2838 | class="cmtt-8">[codebook\_entries]</span><br class="fancyvrb" /><a
|
|---|
| 2839 | id="x1-55014r7"></a><span
|
|---|
| 2840 | class="cmr-6">7</span><span
|
|---|
| 2841 | class="cmtt-8">[codebook\_dimensions]</span><br class="fancyvrb" /><a
|
|---|
| 2842 | id="x1-55016r8"></a><span
|
|---|
| 2843 | class="cmr-6">8</span><span
|
|---|
| 2844 | class="cmtt-8">[codebook\_lookup\_values]</span></div>
|
|---|
| 2845 | <!--l. 347--><p class="noindent" >Decoding (unpacking) a specific vector in the vector lookup table proceeds according to
|
|---|
| 2846 | <span
|
|---|
| 2847 | class="cmtt-12">[codebook</span><span
|
|---|
| 2848 | class="cmtt-12">_lookup</span><span
|
|---|
| 2849 | class="cmtt-12">_type]</span>. The unpacked vector values are what a codebook would return
|
|---|
| 2850 | during audio packet decode in a VQ context.
|
|---|
| 2851 | <!--l. 352--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 2852 | id="x1-560003.2.1"></a><span
|
|---|
| 2853 | class="cmbx-12">Vector value decode: Lookup type 1</span></span>
|
|---|
| 2854 | Lookup type one specifies a lattice VQ lookup table built algorithmically from a list of
|
|---|
| 2855 | scalar values. Calculate (unpack) the final values of a codebook entry vector from
|
|---|
| 2856 | the entries in <span
|
|---|
| 2857 | class="cmtt-12">[codebook</span><span
|
|---|
| 2858 | class="cmtt-12">_multiplicands] </span>as follows (<span
|
|---|
| 2859 | class="cmtt-12">[value</span><span
|
|---|
| 2860 | class="cmtt-12">_vector] </span>is the output
|
|---|
| 2861 | vector representing the vector of values for entry number <span
|
|---|
| 2862 | class="cmtt-12">[lookup</span><span
|
|---|
| 2863 | class="cmtt-12">_offset] </span>in this
|
|---|
| 2864 | codebook):
|
|---|
| 2865 | <!--l. 361--><p class="noindent" >
|
|---|
| 2866 | <div class="fancyvrb" id="fancyvrb18"><a
|
|---|
| 2867 | id="x1-56002r1"></a><span
|
|---|
| 2868 | class="cmr-6">1</span><span
|
|---|
| 2869 | class="cmtt-8"> </span><span
|
|---|
| 2870 | class="cmtt-8"> 1)</span><span
|
|---|
| 2871 | class="cmtt-8"> [last]</span><span
|
|---|
| 2872 | class="cmtt-8"> =</span><span
|
|---|
| 2873 | class="cmtt-8"> 0;</span><br class="fancyvrb" /><a
|
|---|
| 2874 | id="x1-56004r2"></a><span
|
|---|
| 2875 | class="cmr-6">2</span><span
|
|---|
| 2876 | class="cmtt-8"> </span><span
|
|---|
| 2877 | class="cmtt-8"> 2)</span><span
|
|---|
| 2878 | class="cmtt-8"> [index</span><span
|
|---|
| 2879 | class="cmtt-8">_divisor]</span><span
|
|---|
| 2880 | class="cmtt-8"> =</span><span
|
|---|
| 2881 | class="cmtt-8"> 1;</span><br class="fancyvrb" /><a
|
|---|
| 2882 | id="x1-56006r3"></a><span
|
|---|
| 2883 | class="cmr-6">3</span><span
|
|---|
| 2884 | class="cmtt-8"> </span><span
|
|---|
| 2885 | class="cmtt-8"> 3)</span><span
|
|---|
| 2886 | class="cmtt-8"> iterate</span><span
|
|---|
| 2887 | class="cmtt-8"> [i]</span><span
|
|---|
| 2888 | class="cmtt-8"> over</span><span
|
|---|
| 2889 | class="cmtt-8"> the</span><span
|
|---|
| 2890 | class="cmtt-8"> range</span><span
|
|---|
| 2891 | class="cmtt-8"> 0</span><span
|
|---|
| 2892 | class="cmtt-8"> ...</span><span
|
|---|
| 2893 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2894 | class="cmtt-8">_dimensions]-1</span><span
|
|---|
| 2895 | class="cmtt-8"> (once</span><span
|
|---|
| 2896 | class="cmtt-8"> for</span><span
|
|---|
| 2897 | class="cmtt-8"> each</span><span
|
|---|
| 2898 | class="cmtt-8"> scalar</span><span
|
|---|
| 2899 | class="cmtt-8"> value</span><span
|
|---|
| 2900 | class="cmtt-8"> in</span><span
|
|---|
| 2901 | class="cmtt-8"> the</span><span
|
|---|
| 2902 | class="cmtt-8"> value</span><span
|
|---|
| 2903 | class="cmtt-8"> vector)</span><span
|
|---|
| 2904 | class="cmtt-8"> </span><span
|
|---|
| 2905 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 2906 | id="x1-56008r4"></a><span
|
|---|
| 2907 | class="cmr-6">4</span>
|
|---|
| 2908 | <br class="fancyvrb" /><a
|
|---|
| 2909 | id="x1-56010r5"></a><span
|
|---|
| 2910 | class="cmr-6">5</span><span
|
|---|
| 2911 | class="cmtt-8"> </span><span
|
|---|
| 2912 | class="cmtt-8"> </span><span
|
|---|
| 2913 | class="cmtt-8"> </span><span
|
|---|
| 2914 | class="cmtt-8"> </span><span
|
|---|
| 2915 | class="cmtt-8"> </span><span
|
|---|
| 2916 | class="cmtt-8"> </span><span
|
|---|
| 2917 | class="cmtt-8"> 4)</span><span
|
|---|
| 2918 | class="cmtt-8"> [multiplicand</span><span
|
|---|
| 2919 | class="cmtt-8">_offset]</span><span
|
|---|
| 2920 | class="cmtt-8"> =</span><span
|
|---|
| 2921 | class="cmtt-8"> (</span><span
|
|---|
| 2922 | class="cmtt-8"> [lookup</span><span
|
|---|
| 2923 | class="cmtt-8">_offset]</span><span
|
|---|
| 2924 | class="cmtt-8"> divided</span><span
|
|---|
| 2925 | class="cmtt-8"> by</span><span
|
|---|
| 2926 | class="cmtt-8"> [index</span><span
|
|---|
| 2927 | class="cmtt-8">_divisor]</span><span
|
|---|
| 2928 | class="cmtt-8"> using</span><span
|
|---|
| 2929 | class="cmtt-8"> integer</span>
|
|---|
| 2930 | <br class="fancyvrb" /><a
|
|---|
| 2931 | id="x1-56012r6"></a><span
|
|---|
| 2932 | class="cmr-6">6</span><span
|
|---|
| 2933 | class="cmtt-8"> </span><span
|
|---|
| 2934 | class="cmtt-8"> </span><span
|
|---|
| 2935 | class="cmtt-8"> </span><span
|
|---|
| 2936 | class="cmtt-8"> </span><span
|
|---|
| 2937 | class="cmtt-8"> </span><span
|
|---|
| 2938 | class="cmtt-8"> </span><span
|
|---|
| 2939 | class="cmtt-8"> </span><span
|
|---|
| 2940 | class="cmtt-8"> </span><span
|
|---|
| 2941 | class="cmtt-8"> </span><span
|
|---|
| 2942 | class="cmtt-8"> division</span><span
|
|---|
| 2943 | class="cmtt-8"> )</span><span
|
|---|
| 2944 | class="cmtt-8"> integer</span><span
|
|---|
| 2945 | class="cmtt-8"> modulo</span><span
|
|---|
| 2946 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2947 | class="cmtt-8">_lookup</span><span
|
|---|
| 2948 | class="cmtt-8">_values]</span><br class="fancyvrb" /><a
|
|---|
| 2949 | id="x1-56014r7"></a><span
|
|---|
| 2950 | class="cmr-6">7</span><br class="fancyvrb" /><a
|
|---|
| 2951 | id="x1-56016r8"></a><span
|
|---|
| 2952 | class="cmr-6">8</span><span
|
|---|
| 2953 | class="cmtt-8"> </span><span
|
|---|
| 2954 | class="cmtt-8"> </span><span
|
|---|
| 2955 | class="cmtt-8"> </span><span
|
|---|
| 2956 | class="cmtt-8"> </span><span
|
|---|
| 2957 | class="cmtt-8"> </span><span
|
|---|
| 2958 | class="cmtt-8"> </span><span
|
|---|
| 2959 | class="cmtt-8"> 5)</span><span
|
|---|
| 2960 | class="cmtt-8"> vector</span><span
|
|---|
| 2961 | class="cmtt-8"> [value</span><span
|
|---|
| 2962 | class="cmtt-8">_vector]</span><span
|
|---|
| 2963 | class="cmtt-8"> element</span><span
|
|---|
| 2964 | class="cmtt-8"> [i]</span><span
|
|---|
| 2965 | class="cmtt-8"> =</span>
|
|---|
| 2966 | <br class="fancyvrb" /><a
|
|---|
| 2967 | id="x1-56018r9"></a><span
|
|---|
| 2968 | class="cmr-6">9</span><span
|
|---|
| 2969 | class="cmtt-8"> </span><span
|
|---|
| 2970 | class="cmtt-8"> </span><span
|
|---|
| 2971 | class="cmtt-8"> </span><span
|
|---|
| 2972 | class="cmtt-8"> </span><span
|
|---|
| 2973 | class="cmtt-8"> </span><span
|
|---|
| 2974 | class="cmtt-8"> </span><span
|
|---|
| 2975 | class="cmtt-8"> </span><span
|
|---|
| 2976 | class="cmtt-8"> </span><span
|
|---|
| 2977 | class="cmtt-8"> </span><span
|
|---|
| 2978 | class="cmtt-8"> </span><span
|
|---|
| 2979 | class="cmtt-8"> </span><span
|
|---|
| 2980 | class="cmtt-8"> (</span><span
|
|---|
| 2981 | class="cmtt-8"> [codebook</span><span
|
|---|
| 2982 | class="cmtt-8">_multiplicands]</span><span
|
|---|
| 2983 | class="cmtt-8"> array</span><span
|
|---|
| 2984 | class="cmtt-8"> element</span><span
|
|---|
| 2985 | class="cmtt-8"> number</span><span
|
|---|
| 2986 | class="cmtt-8"> [multiplicand</span><span
|
|---|
| 2987 | class="cmtt-8">_offset]</span><span
|
|---|
| 2988 | class="cmtt-8"> )</span><span
|
|---|
| 2989 | class="cmtt-8"> *</span>
|
|---|
| 2990 | <br class="fancyvrb" /><a
|
|---|
| 2991 | id="x1-56020r10"></a><span
|
|---|
| 2992 | class="cmr-6">10</span><span
|
|---|
| 2993 | class="cmtt-8"> </span><span
|
|---|
| 2994 | class="cmtt-8"> </span><span
|
|---|
| 2995 | class="cmtt-8"> </span><span
|
|---|
| 2996 | class="cmtt-8"> </span><span
|
|---|
| 2997 | class="cmtt-8"> </span><span
|
|---|
| 2998 | class="cmtt-8"> </span><span
|
|---|
| 2999 | class="cmtt-8"> </span><span
|
|---|
| 3000 | class="cmtt-8"> </span><span
|
|---|
| 3001 | class="cmtt-8"> </span><span
|
|---|
| 3002 | class="cmtt-8"> </span><span
|
|---|
| 3003 | class="cmtt-8"> </span><span
|
|---|
| 3004 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3005 | class="cmtt-8">_delta</span><span
|
|---|
| 3006 | class="cmtt-8">_value]</span><span
|
|---|
| 3007 | class="cmtt-8"> +</span><span
|
|---|
| 3008 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3009 | class="cmtt-8">_minimum</span><span
|
|---|
| 3010 | class="cmtt-8">_value]</span><span
|
|---|
| 3011 | class="cmtt-8"> +</span><span
|
|---|
| 3012 | class="cmtt-8"> [last];</span><br class="fancyvrb" /><a
|
|---|
| 3013 | id="x1-56022r11"></a><span
|
|---|
| 3014 | class="cmr-6">11</span>
|
|---|
| 3015 | <br class="fancyvrb" /><a
|
|---|
| 3016 | id="x1-56024r12"></a><span
|
|---|
| 3017 | class="cmr-6">12</span><span
|
|---|
| 3018 | class="cmtt-8"> </span><span
|
|---|
| 3019 | class="cmtt-8"> </span><span
|
|---|
| 3020 | class="cmtt-8"> </span><span
|
|---|
| 3021 | class="cmtt-8"> </span><span
|
|---|
| 3022 | class="cmtt-8"> </span><span
|
|---|
| 3023 | class="cmtt-8"> </span><span
|
|---|
| 3024 | class="cmtt-8"> 6)</span><span
|
|---|
| 3025 | class="cmtt-8"> if</span><span
|
|---|
| 3026 | class="cmtt-8"> (</span><span
|
|---|
| 3027 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3028 | class="cmtt-8">_sequence</span><span
|
|---|
| 3029 | class="cmtt-8">_p]</span><span
|
|---|
| 3030 | class="cmtt-8"> is</span><span
|
|---|
| 3031 | class="cmtt-8"> set</span><span
|
|---|
| 3032 | class="cmtt-8"> )</span><span
|
|---|
| 3033 | class="cmtt-8"> then</span><span
|
|---|
| 3034 | class="cmtt-8"> set</span><span
|
|---|
| 3035 | class="cmtt-8"> [last]</span><span
|
|---|
| 3036 | class="cmtt-8"> =</span><span
|
|---|
| 3037 | class="cmtt-8"> vector</span><span
|
|---|
| 3038 | class="cmtt-8"> [value</span><span
|
|---|
| 3039 | class="cmtt-8">_vector]</span><span
|
|---|
| 3040 | class="cmtt-8"> element</span><span
|
|---|
| 3041 | class="cmtt-8"> [i]</span><br class="fancyvrb" /><a
|
|---|
| 3042 | id="x1-56026r13"></a><span
|
|---|
| 3043 | class="cmr-6">13</span>
|
|---|
| 3044 | <br class="fancyvrb" /><a
|
|---|
| 3045 | id="x1-56028r14"></a><span
|
|---|
| 3046 | class="cmr-6">14</span><span
|
|---|
| 3047 | class="cmtt-8"> </span><span
|
|---|
| 3048 | class="cmtt-8"> </span><span
|
|---|
| 3049 | class="cmtt-8"> </span><span
|
|---|
| 3050 | class="cmtt-8"> </span><span
|
|---|
| 3051 | class="cmtt-8"> </span><span
|
|---|
| 3052 | class="cmtt-8"> </span><span
|
|---|
| 3053 | class="cmtt-8"> 7)</span><span
|
|---|
| 3054 | class="cmtt-8"> [index</span><span
|
|---|
| 3055 | class="cmtt-8">_divisor]</span><span
|
|---|
| 3056 | class="cmtt-8"> =</span><span
|
|---|
| 3057 | class="cmtt-8"> [index</span><span
|
|---|
| 3058 | class="cmtt-8">_divisor]</span><span
|
|---|
| 3059 | class="cmtt-8"> *</span><span
|
|---|
| 3060 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3061 | class="cmtt-8">_lookup</span><span
|
|---|
| 3062 | class="cmtt-8">_values]</span><br class="fancyvrb" /><a
|
|---|
| 3063 | id="x1-56030r15"></a><span
|
|---|
| 3064 | class="cmr-6">15</span><br class="fancyvrb" /><a
|
|---|
| 3065 | id="x1-56032r16"></a><span
|
|---|
| 3066 | class="cmr-6">16</span><span
|
|---|
| 3067 | class="cmtt-8"> </span><span
|
|---|
| 3068 | class="cmtt-8"> </span><span
|
|---|
| 3069 | class="cmtt-8"> </span><span
|
|---|
| 3070 | class="cmtt-8"> </span><span
|
|---|
| 3071 | class="cmtt-8"> </span><span
|
|---|
| 3072 | class="cmsy-8">}</span><br class="fancyvrb" /><a
|
|---|
| 3073 | id="x1-56034r17"></a><span
|
|---|
| 3074 | class="cmr-6">17</span><br class="fancyvrb" /><a
|
|---|
| 3075 | id="x1-56036r18"></a><span
|
|---|
| 3076 | class="cmr-6">18</span><span
|
|---|
| 3077 | class="cmtt-8"> </span><span
|
|---|
| 3078 | class="cmtt-8"> 8)</span><span
|
|---|
| 3079 | class="cmtt-8"> vector</span><span
|
|---|
| 3080 | class="cmtt-8"> calculation</span><span
|
|---|
| 3081 | class="cmtt-8"> completed.</span></div>
|
|---|
| 3082 | <!--l. 384--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 3083 | id="x1-570003.2.1"></a><span
|
|---|
| 3084 | class="cmbx-12">Vector value decode: Lookup type 2</span></span>
|
|---|
| 3085 | Lookup type two specifies a VQ lookup table in which each scalar in each vector is explicitly set
|
|---|
| 3086 | by the <span
|
|---|
| 3087 | class="cmtt-12">[codebook</span><span
|
|---|
| 3088 | class="cmtt-12">_multiplicands] </span>array in a one-to-one mapping. Calculate [unpack] the final
|
|---|
| 3089 | values of a codebook entry vector from the entries in <span
|
|---|
| 3090 | class="cmtt-12">[codebook</span><span
|
|---|
| 3091 | class="cmtt-12">_multiplicands] </span>as follows
|
|---|
| 3092 | (<span
|
|---|
| 3093 | class="cmtt-12">[value</span><span
|
|---|
| 3094 | class="cmtt-12">_vector] </span>is the output vector representing the vector of values for entry number
|
|---|
| 3095 | <span
|
|---|
| 3096 | class="cmtt-12">[lookup</span><span
|
|---|
| 3097 | class="cmtt-12">_offset] </span>in this codebook):
|
|---|
| 3098 | <!--l. 394--><p class="noindent" >
|
|---|
| 3099 | <div class="fancyvrb" id="fancyvrb19"><a
|
|---|
| 3100 | id="x1-57002r1"></a><span
|
|---|
| 3101 | class="cmr-6">1</span><span
|
|---|
| 3102 | class="cmtt-8"> </span><span
|
|---|
| 3103 | class="cmtt-8"> 1)</span><span
|
|---|
| 3104 | class="cmtt-8"> [last]</span><span
|
|---|
| 3105 | class="cmtt-8"> =</span><span
|
|---|
| 3106 | class="cmtt-8"> 0;</span><br class="fancyvrb" /><a
|
|---|
| 3107 | id="x1-57004r2"></a><span
|
|---|
| 3108 | class="cmr-6">2</span><span
|
|---|
| 3109 | class="cmtt-8"> </span><span
|
|---|
| 3110 | class="cmtt-8"> 2)</span><span
|
|---|
| 3111 | class="cmtt-8"> [multiplicand</span><span
|
|---|
| 3112 | class="cmtt-8">_offset]</span><span
|
|---|
| 3113 | class="cmtt-8"> =</span><span
|
|---|
| 3114 | class="cmtt-8"> [lookup</span><span
|
|---|
| 3115 | class="cmtt-8">_offset]</span><span
|
|---|
| 3116 | class="cmtt-8"> *</span><span
|
|---|
| 3117 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3118 | class="cmtt-8">_dimensions]</span>
|
|---|
| 3119 | <br class="fancyvrb" /><a
|
|---|
| 3120 | id="x1-57006r3"></a><span
|
|---|
| 3121 | class="cmr-6">3</span><span
|
|---|
| 3122 | class="cmtt-8"> </span><span
|
|---|
| 3123 | class="cmtt-8"> 3)</span><span
|
|---|
| 3124 | class="cmtt-8"> iterate</span><span
|
|---|
| 3125 | class="cmtt-8"> [i]</span><span
|
|---|
| 3126 | class="cmtt-8"> over</span><span
|
|---|
| 3127 | class="cmtt-8"> the</span><span
|
|---|
| 3128 | class="cmtt-8"> range</span><span
|
|---|
| 3129 | class="cmtt-8"> 0</span><span
|
|---|
| 3130 | class="cmtt-8"> ...</span><span
|
|---|
| 3131 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3132 | class="cmtt-8">_dimensions]-1</span><span
|
|---|
| 3133 | class="cmtt-8"> (once</span><span
|
|---|
| 3134 | class="cmtt-8"> for</span><span
|
|---|
| 3135 | class="cmtt-8"> each</span><span
|
|---|
| 3136 | class="cmtt-8"> scalar</span><span
|
|---|
| 3137 | class="cmtt-8"> value</span><span
|
|---|
| 3138 | class="cmtt-8"> in</span><span
|
|---|
| 3139 | class="cmtt-8"> the</span><span
|
|---|
| 3140 | class="cmtt-8"> value</span><span
|
|---|
| 3141 | class="cmtt-8"> vector)</span><span
|
|---|
| 3142 | class="cmtt-8"> </span><span
|
|---|
| 3143 | class="cmsy-8">{</span><br class="fancyvrb" /><a
|
|---|
| 3144 | id="x1-57008r4"></a><span
|
|---|
| 3145 | class="cmr-6">4</span>
|
|---|
| 3146 | <br class="fancyvrb" /><a
|
|---|
| 3147 | id="x1-57010r5"></a><span
|
|---|
| 3148 | class="cmr-6">5</span><span
|
|---|
| 3149 | class="cmtt-8"> </span><span
|
|---|
| 3150 | class="cmtt-8"> </span><span
|
|---|
| 3151 | class="cmtt-8"> </span><span
|
|---|
| 3152 | class="cmtt-8"> </span><span
|
|---|
| 3153 | class="cmtt-8"> </span><span
|
|---|
| 3154 | class="cmtt-8"> </span><span
|
|---|
| 3155 | class="cmtt-8"> 4)</span><span
|
|---|
| 3156 | class="cmtt-8"> vector</span><span
|
|---|
| 3157 | class="cmtt-8"> [value</span><span
|
|---|
| 3158 | class="cmtt-8">_vector]</span><span
|
|---|
| 3159 | class="cmtt-8"> element</span><span
|
|---|
| 3160 | class="cmtt-8"> [i]</span><span
|
|---|
| 3161 | class="cmtt-8"> =</span><br class="fancyvrb" /><a
|
|---|
| 3162 | id="x1-57012r6"></a><span
|
|---|
| 3163 | class="cmr-6">6</span><span
|
|---|
| 3164 | class="cmtt-8"> </span><span
|
|---|
| 3165 | class="cmtt-8"> </span><span
|
|---|
| 3166 | class="cmtt-8"> </span><span
|
|---|
| 3167 | class="cmtt-8"> </span><span
|
|---|
| 3168 | class="cmtt-8"> </span><span
|
|---|
| 3169 | class="cmtt-8"> </span><span
|
|---|
| 3170 | class="cmtt-8"> </span><span
|
|---|
| 3171 | class="cmtt-8"> </span><span
|
|---|
| 3172 | class="cmtt-8"> </span><span
|
|---|
| 3173 | class="cmtt-8"> </span><span
|
|---|
| 3174 | class="cmtt-8"> </span><span
|
|---|
| 3175 | class="cmtt-8"> (</span><span
|
|---|
| 3176 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3177 | class="cmtt-8">_multiplicands]</span><span
|
|---|
| 3178 | class="cmtt-8"> array</span><span
|
|---|
| 3179 | class="cmtt-8"> element</span><span
|
|---|
| 3180 | class="cmtt-8"> number</span><span
|
|---|
| 3181 | class="cmtt-8"> [multiplicand</span><span
|
|---|
| 3182 | class="cmtt-8">_offset]</span><span
|
|---|
| 3183 | class="cmtt-8"> )</span><span
|
|---|
| 3184 | class="cmtt-8"> *</span>
|
|---|
| 3185 | <br class="fancyvrb" /><a
|
|---|
| 3186 | id="x1-57014r7"></a><span
|
|---|
| 3187 | class="cmr-6">7</span><span
|
|---|
| 3188 | class="cmtt-8"> </span><span
|
|---|
| 3189 | class="cmtt-8"> </span><span
|
|---|
| 3190 | class="cmtt-8"> </span><span
|
|---|
| 3191 | class="cmtt-8"> </span><span
|
|---|
| 3192 | class="cmtt-8"> </span><span
|
|---|
| 3193 | class="cmtt-8"> </span><span
|
|---|
| 3194 | class="cmtt-8"> </span><span
|
|---|
| 3195 | class="cmtt-8"> </span><span
|
|---|
| 3196 | class="cmtt-8"> </span><span
|
|---|
| 3197 | class="cmtt-8"> </span><span
|
|---|
| 3198 | class="cmtt-8"> </span><span
|
|---|
| 3199 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3200 | class="cmtt-8">_delta</span><span
|
|---|
| 3201 | class="cmtt-8">_value]</span><span
|
|---|
| 3202 | class="cmtt-8"> +</span><span
|
|---|
| 3203 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3204 | class="cmtt-8">_minimum</span><span
|
|---|
| 3205 | class="cmtt-8">_value]</span><span
|
|---|
| 3206 | class="cmtt-8"> +</span><span
|
|---|
| 3207 | class="cmtt-8"> [last];</span><br class="fancyvrb" /><a
|
|---|
| 3208 | id="x1-57016r8"></a><span
|
|---|
| 3209 | class="cmr-6">8</span>
|
|---|
| 3210 | <br class="fancyvrb" /><a
|
|---|
| 3211 | id="x1-57018r9"></a><span
|
|---|
| 3212 | class="cmr-6">9</span><span
|
|---|
| 3213 | class="cmtt-8"> </span><span
|
|---|
| 3214 | class="cmtt-8"> </span><span
|
|---|
| 3215 | class="cmtt-8"> </span><span
|
|---|
| 3216 | class="cmtt-8"> </span><span
|
|---|
| 3217 | class="cmtt-8"> </span><span
|
|---|
| 3218 | class="cmtt-8"> </span><span
|
|---|
| 3219 | class="cmtt-8"> 5)</span><span
|
|---|
| 3220 | class="cmtt-8"> if</span><span
|
|---|
| 3221 | class="cmtt-8"> (</span><span
|
|---|
| 3222 | class="cmtt-8"> [codebook</span><span
|
|---|
| 3223 | class="cmtt-8">_sequence</span><span
|
|---|
| 3224 | class="cmtt-8">_p]</span><span
|
|---|
| 3225 | class="cmtt-8"> is</span><span
|
|---|
| 3226 | class="cmtt-8"> set</span><span
|
|---|
| 3227 | class="cmtt-8"> )</span><span
|
|---|
| 3228 | class="cmtt-8"> then</span><span
|
|---|
| 3229 | class="cmtt-8"> set</span><span
|
|---|
| 3230 | class="cmtt-8"> [last]</span><span
|
|---|
| 3231 | class="cmtt-8"> =</span><span
|
|---|
| 3232 | class="cmtt-8"> vector</span><span
|
|---|
| 3233 | class="cmtt-8"> [value</span><span
|
|---|
| 3234 | class="cmtt-8">_vector]</span><span
|
|---|
| 3235 | class="cmtt-8"> element</span><span
|
|---|
| 3236 | class="cmtt-8"> [i]</span><br class="fancyvrb" /><a
|
|---|
| 3237 | id="x1-57020r10"></a><span
|
|---|
| 3238 | class="cmr-6">10</span>
|
|---|
| 3239 | <br class="fancyvrb" /><a
|
|---|
| 3240 | id="x1-57022r11"></a><span
|
|---|
| 3241 | class="cmr-6">11</span><span
|
|---|
| 3242 | class="cmtt-8"> </span><span
|
|---|
| 3243 | class="cmtt-8"> </span><span
|
|---|
| 3244 | class="cmtt-8"> </span><span
|
|---|
| 3245 | class="cmtt-8"> </span><span
|
|---|
| 3246 | class="cmtt-8"> </span><span
|
|---|
| 3247 | class="cmtt-8"> </span><span
|
|---|
| 3248 | class="cmtt-8"> 6)</span><span
|
|---|
| 3249 | class="cmtt-8"> increment</span><span
|
|---|
| 3250 | class="cmtt-8"> [multiplicand</span><span
|
|---|
| 3251 | class="cmtt-8">_offset]</span><br class="fancyvrb" /><a
|
|---|
| 3252 | id="x1-57024r12"></a><span
|
|---|
| 3253 | class="cmr-6">12</span><br class="fancyvrb" /><a
|
|---|
| 3254 | id="x1-57026r13"></a><span
|
|---|
| 3255 | class="cmr-6">13</span><span
|
|---|
| 3256 | class="cmtt-8"> </span><span
|
|---|
| 3257 | class="cmtt-8"> </span><span
|
|---|
| 3258 | class="cmtt-8"> </span><span
|
|---|
| 3259 | class="cmtt-8"> </span><span
|
|---|
| 3260 | class="cmtt-8"> </span><span
|
|---|
| 3261 | class="cmsy-8">}</span><br class="fancyvrb" /><a
|
|---|
| 3262 | id="x1-57028r14"></a><span
|
|---|
| 3263 | class="cmr-6">14</span><br class="fancyvrb" /><a
|
|---|
| 3264 | id="x1-57030r15"></a><span
|
|---|
| 3265 | class="cmr-6">15</span><span
|
|---|
| 3266 | class="cmtt-8"> </span><span
|
|---|
| 3267 | class="cmtt-8"> 7)</span><span
|
|---|
| 3268 | class="cmtt-8"> vector</span><span
|
|---|
| 3269 | class="cmtt-8"> calculation</span><span
|
|---|
| 3270 | class="cmtt-8"> completed.</span></div>
|
|---|
| 3271 |
|
|---|
| 3272 |
|
|---|
| 3273 |
|
|---|
| 3274 | <!--l. 420--><p class="noindent" >
|
|---|
| 3275 | <h4 class="subsectionHead"><span class="titlemark">3.3. </span> <a
|
|---|
| 3276 | id="x1-580003.3"></a>Use of the codebook abstraction</h4>
|
|---|
| 3277 | <!--l. 422--><p class="noindent" >The decoder uses the codebook abstraction much as it does the bit-unpacking convention; a
|
|---|
| 3278 | specific codebook reads a codeword from the bitstream, decoding it into an entry number, and
|
|---|
| 3279 | then returns that entry number to the decoder (when used in a scalar entropy coding context), or
|
|---|
| 3280 | uses that entry number as an offset into the VQ lookup table, returning a vector of values (when
|
|---|
| 3281 | used in a context desiring a VQ value). Scalar or VQ context is always explicit; any
|
|---|
| 3282 | call to the codebook mechanism requests either a scalar entry number or a lookup
|
|---|
| 3283 | vector.
|
|---|
| 3284 | <!--l. 432--><p class="noindent" >Note that VQ lookup type zero indicates that there is no lookup table; requesting
|
|---|
| 3285 | decode using a codebook of lookup type 0 in any context expecting a vector return
|
|---|
| 3286 | value (even in a case where a vector of dimension one) is forbidden. If decoder setup
|
|---|
| 3287 | or decode requests such an action, that is an error condition rendering the packet
|
|---|
| 3288 | undecodable.
|
|---|
| 3289 | <!--l. 439--><p class="noindent" >Using a codebook to read from the packet bitstream consists first of reading and decoding the
|
|---|
| 3290 | next codeword in the bitstream. The decoder reads bits until the accumulated bits match a
|
|---|
| 3291 | codeword in the codebook. This process can be though of as logically walking the
|
|---|
| 3292 | Huffman decode tree by reading one bit at a time from the bitstream, and using the
|
|---|
| 3293 | bit as a decision boolean to take the 0 branch (left in the above examples) or the 1
|
|---|
| 3294 | branch (right in the above examples). Walking the tree finishes when the decode process
|
|---|
| 3295 | hits a leaf in the decision tree; the result is the entry number corresponding to that
|
|---|
| 3296 | leaf. Reading past the end of a packet propagates the ’end-of-stream’ condition to the
|
|---|
| 3297 | decoder.
|
|---|
| 3298 | <!--l. 451--><p class="noindent" >When used in a scalar context, the resulting codeword entry is the desired return
|
|---|
| 3299 | value.
|
|---|
| 3300 | <!--l. 454--><p class="noindent" >When used in a VQ context, the codeword entry number is used as an offset into the VQ lookup
|
|---|
| 3301 | table. The value returned to the decoder is the vector of scalars corresponding to this
|
|---|
| 3302 | offset.
|
|---|
| 3303 |
|
|---|
| 3304 |
|
|---|
| 3305 |
|
|---|
| 3306 |
|
|---|
| 3307 |
|
|---|
| 3308 |
|
|---|
| 3309 | <h3 class="sectionHead"><span class="titlemark">4. </span> <a
|
|---|
| 3310 | id="x1-590004"></a>Codec Setup and Packet Decode</h3>
|
|---|
| 3311 | <!--l. 6--><p class="noindent" >
|
|---|
| 3312 | <h4 class="subsectionHead"><span class="titlemark">4.1. </span> <a
|
|---|
| 3313 | id="x1-600004.1"></a>Overview</h4>
|
|---|
| 3314 | <!--l. 8--><p class="noindent" >This document serves as the top-level reference document for the bit-by-bit decode specification
|
|---|
| 3315 | of Vorbis I. This document assumes a high-level understanding of the Vorbis decode
|
|---|
| 3316 | process, which is provided in <a
|
|---|
| 3317 | href="#x1-20001">section 1</a>, “<a
|
|---|
| 3318 | href="#x1-20001">Introduction and Description<!--tex4ht:ref: vorbis:spec:intro --></a>”. <a
|
|---|
| 3319 | href="#x1-360002">section 2</a>,
|
|---|
| 3320 | “<a
|
|---|
| 3321 | href="#x1-360002">Bitpacking Convention<!--tex4ht:ref: vorbis:spec:bitpacking --></a>” covers reading and writing bit fields from and to bitstream
|
|---|
| 3322 | packets.
|
|---|
| 3323 | <!--l. 16--><p class="noindent" >
|
|---|
| 3324 | <h4 class="subsectionHead"><span class="titlemark">4.2. </span> <a
|
|---|
| 3325 | id="x1-610004.2"></a>Header decode and decode setup</h4>
|
|---|
| 3326 | <!--l. 18--><p class="noindent" >A Vorbis bitstream begins with three header packets. The header packets are, in order, the
|
|---|
| 3327 | identification header, the comments header, and the setup header. All are required for decode
|
|---|
| 3328 | compliance. An end-of-packet condition during decoding the first or third header packet renders
|
|---|
| 3329 | the stream undecodable. End-of-packet decoding the comment header is a non-fatal error
|
|---|
| 3330 | condition.
|
|---|
| 3331 | <!--l. 25--><p class="noindent" >
|
|---|
| 3332 | <h5 class="subsubsectionHead"><span class="titlemark">4.2.1. </span> <a
|
|---|
| 3333 | id="x1-620004.2.1"></a>Common header decode</h5>
|
|---|
| 3334 | <!--l. 27--><p class="noindent" >Each header packet begins with the same header fields.
|
|---|
| 3335 | <!--l. 30--><p class="noindent" >
|
|---|
| 3336 | <div class="fancyvrb" id="fancyvrb20"><a
|
|---|
| 3337 | id="x1-62002r1"></a><span
|
|---|
| 3338 | class="cmr-6">1</span><span
|
|---|
| 3339 | class="cmtt-8"> </span><span
|
|---|
| 3340 | class="cmtt-8"> 1)</span><span
|
|---|
| 3341 | class="cmtt-8"> [packet</span><span
|
|---|
| 3342 | class="cmtt-8">_type]</span><span
|
|---|
| 3343 | class="cmtt-8"> :</span><span
|
|---|
| 3344 | class="cmtt-8"> 8</span><span
|
|---|
| 3345 | class="cmtt-8"> bit</span><span
|
|---|
| 3346 | class="cmtt-8"> value</span><br class="fancyvrb" /><a
|
|---|
| 3347 | id="x1-62004r2"></a><span
|
|---|
| 3348 | class="cmr-6">2</span><span
|
|---|
| 3349 | class="cmtt-8"> </span><span
|
|---|
| 3350 | class="cmtt-8"> 2)</span><span
|
|---|
| 3351 | class="cmtt-8"> 0x76,</span><span
|
|---|
| 3352 | class="cmtt-8"> 0x6f,</span><span
|
|---|
| 3353 | class="cmtt-8"> 0x72,</span><span
|
|---|
| 3354 | class="cmtt-8"> 0x62,</span><span
|
|---|
| 3355 | class="cmtt-8"> 0x69,</span><span
|
|---|
| 3356 | class="cmtt-8"> 0x73:</span><span
|
|---|
| 3357 | class="cmtt-8"> the</span><span
|
|---|
| 3358 | class="cmtt-8"> characters</span><span
|
|---|
| 3359 | class="cmtt-8"> ’v’,’o’,’r’,’b’,’i’,’s’</span><span
|
|---|
| 3360 | class="cmtt-8"> as</span><span
|
|---|
| 3361 | class="cmtt-8"> six</span><span
|
|---|
| 3362 | class="cmtt-8"> octets</span></div>
|
|---|
| 3363 | <!--l. 35--><p class="noindent" >Decode continues according to packet type; the identification header is type 1, the comment
|
|---|
| 3364 | header type 3 and the setup header type 5 (these types are all odd as a packet with a leading
|
|---|
| 3365 | single bit of ’0’ is an audio packet). The packets must occur in the order of identification,
|
|---|
| 3366 |
|
|---|
| 3367 |
|
|---|
| 3368 |
|
|---|
| 3369 | comment, setup.
|
|---|
| 3370 | <!--l. 43--><p class="noindent" >
|
|---|
| 3371 | <h5 class="subsubsectionHead"><span class="titlemark">4.2.2. </span> <a
|
|---|
| 3372 | id="x1-630004.2.2"></a>Identification header</h5>
|
|---|
| 3373 | <!--l. 45--><p class="noindent" >The identification header is a short header of only a few fields used to declare the stream
|
|---|
| 3374 | definitively as Vorbis, and provide a few externally relevant pieces of information about the audio
|
|---|
| 3375 | stream. The identification header is coded as follows:
|
|---|
| 3376 | <!--l. 50--><p class="noindent" >
|
|---|
| 3377 | <div class="fancyvrb" id="fancyvrb21"><a
|
|---|
| 3378 | id="x1-63002r1"></a><span
|
|---|
| 3379 | class="cmr-6">1</span><span
|
|---|
| 3380 | class="cmtt-8"> 1)</span><span
|
|---|
| 3381 | class="cmtt-8"> [vorbis</span><span
|
|---|
| 3382 | class="cmtt-8">_version]</span><span
|
|---|
| 3383 | class="cmtt-8"> =</span><span
|
|---|
| 3384 | class="cmtt-8"> read</span><span
|
|---|
| 3385 | class="cmtt-8"> 32</span><span
|
|---|
| 3386 | class="cmtt-8"> bits</span><span
|
|---|
| 3387 | class="cmtt-8"> as</span><span
|
|---|
| 3388 | class="cmtt-8"> unsigned</span><span
|
|---|
| 3389 | class="cmtt-8"> integer</span><br class="fancyvrb" /><a
|
|---|
| 3390 | id="x1-63004r2"></a><span
|
|---|
| 3391 | class="cmr-6">2</span><span
|
|---|
| 3392 | class="cmtt-8"> 2)</span><span
|
|---|
| 3393 | class="cmtt-8"> [audio</span><span
|
|---|
| 3394 | class="cmtt-8">_channels]</span><span
|
|---|
| 3395 | class="cmtt-8"> =</span><span
|
|---|
| 3396 | class="cmtt-8"> read</span><span
|
|---|
| 3397 | class="cmtt-8"> 8</span><span
|
|---|
| 3398 | class="cmtt-8"> bit</span><span
|
|---|
| 3399 | class="cmtt-8"> integer</span><span
|
|---|
| 3400 | class="cmtt-8"> as</span><span
|
|---|
| 3401 | class="cmtt-8"> unsigned</span>
|
|---|
| 3402 | <br class="fancyvrb" /><a
|
|---|
| 3403 | id="x1-63006r3"></a><span
|
|---|
| 3404 | class="cmr-6">3</span><span
|
|---|
| 3405 | class="cmtt-8"> 3)</span><span
|
|---|
| 3406 | class="cmtt-8"> [audio</span><span
|
|---|
| 3407 | class="cmtt-8">_sample</span><span
|
|---|
| 3408 | class="cmtt-8">_rate]</span><span
|
|---|
| 3409 | class="cmtt-8"> =</span><span
|
|---|
| 3410 | class="cmtt-8"> read</span><span
|
|---|
| 3411 | class="cmtt-8"> 32</span><span
|
|---|
| 3412 | class="cmtt-8"> bits</span><span
|
|---|
| 3413 | class="cmtt-8"> as</span><span
|
|---|
| 3414 | class="cmtt-8"> unsigned</span><span
|
|---|
| 3415 | class="cmtt-8"> integer</span><br class="fancyvrb" /><a
|
|---|
| 3416 | id="x1-63008r4"></a><span
|
|---|
| 3417 | class="cmr-6">4</span><span
|
|---|
| 3418 | class="cmtt-8"> 4)</span><span
|
|---|
| 3419 | class="cmtt-8"> [bitrate</span><span
|
|---|
| 3420 | class="cmtt-8">_maximum]</span><span
|
|---|
| 3421 | class="cmtt-8"> =</span><span
|
|---|
| 3422 | class="cmtt-8"> read</span><span
|
|---|
| 3423 | class="cmtt-8"> 32</span><span
|
|---|
| 3424 | class="cmtt-8"> bits</span><span
|
|---|
| 3425 | class="cmtt-8"> as</span><span
|
|---|
| 3426 | class="cmtt-8"> signed</span><span
|
|---|
| 3427 | class="cmtt-8"> integer</span>
|
|---|
| 3428 | <br class="fancyvrb" /><a
|
|---|
| 3429 | id="x1-63010r5"></a><span
|
|---|
| 3430 | class="cmr-6">5</span><span
|
|---|
| 3431 | class="cmtt-8"> 5)</span><span
|
|---|
| 3432 | class="cmtt-8"> [bitrate</span><span
|
|---|
| 3433 | class="cmtt-8">_nominal]</span><span
|
|---|
| 3434 | class="cmtt-8"> =</span><span
|
|---|
| 3435 | class="cmtt-8"> read</span><span
|
|---|
| 3436 | class="cmtt-8"> 32</span><span
|
|---|
| 3437 | class="cmtt-8"> bits</span><span
|
|---|
| 3438 | class="cmtt-8"> as</span><span
|
|---|
| 3439 | class="cmtt-8"> signed</span><span
|
|---|
| 3440 | class="cmtt-8"> integer</span><br class="fancyvrb" /><a
|
|---|
| 3441 | id="x1-63012r6"></a><span
|
|---|
| 3442 | class="cmr-6">6</span><span
|
|---|
| 3443 | class="cmtt-8"> 6)</span><span
|
|---|
| 3444 | class="cmtt-8"> [bitrate</span><span
|
|---|
| 3445 | class="cmtt-8">_minimum]</span><span
|
|---|
| 3446 | class="cmtt-8"> =</span><span
|
|---|
| 3447 | class="cmtt-8"> read</span><span
|
|---|
| 3448 | class="cmtt-8"> 32</span><span
|
|---|
| 3449 | class="cmtt-8"> bits</span><span
|
|---|
| 3450 | class="cmtt-8"> as</span><span
|
|---|
| 3451 | class="cmtt-8"> signed</span><span
|
|---|
| 3452 | class="cmtt-8"> integer</span>
|
|---|
| 3453 | <br class="fancyvrb" /><a
|
|---|
| 3454 | id="x1-63014r7"></a><span
|
|---|
| 3455 | class="cmr-6">7</span><span
|
|---|
| 3456 | class="cmtt-8"> 7)</span><span
|
|---|
| 3457 | class="cmtt-8"> [blocksize</span><span
|
|---|
| 3458 | class="cmtt-8">_0]</span><span
|
|---|
| 3459 | class="cmtt-8"> =</span><span
|
|---|
| 3460 | class="cmtt-8"> 2</span><span
|
|---|
| 3461 | class="cmtt-8"> exponent</span><span
|
|---|
| 3462 | class="cmtt-8"> (read</span><span
|
|---|
| 3463 | class="cmtt-8"> 4</span><span
|
|---|
| 3464 | class="cmtt-8"> bits</span><span
|
|---|
| 3465 | class="cmtt-8"> as</span><span
|
|---|
| 3466 | class="cmtt-8"> unsigned</span><span
|
|---|
| 3467 | class="cmtt-8"> integer)</span><br class="fancyvrb" /><a
|
|---|
| 3468 | id="x1-63016r8"></a><span
|
|---|
| 3469 | class="cmr-6">8</span><span
|
|---|
| 3470 | class="cmtt-8"> 8)</span><span
|
|---|
| 3471 | class="cmtt-8"> [blocksize</span><span
|
|---|
| 3472 | class="cmtt-8">_1]</span><span
|
|---|
| 3473 | class="cmtt-8"> =</span><span
|
|---|
| 3474 | class="cmtt-8"> 2</span><span
|
|---|
| 3475 | class="cmtt-8"> exponent</span><span
|
|---|
| 3476 | class="cmtt-8"> (read</span><span
|
|---|
| 3477 | class="cmtt-8"> 4</span><span
|
|---|
| 3478 | class="cmtt-8"> bits</span><span
|
|---|
| 3479 | class="cmtt-8"> as</span><span
|
|---|
| 3480 | class="cmtt-8"> unsigned</span><span
|
|---|
| 3481 | class="cmtt-8"> integer)</span>
|
|---|
| 3482 | <br class="fancyvrb" /><a
|
|---|
| 3483 | id="x1-63018r9"></a><span
|
|---|
| 3484 | class="cmr-6">9</span><span
|
|---|
| 3485 | class="cmtt-8"> 9)</span><span
|
|---|
| 3486 | class="cmtt-8"> [framing</span><span
|
|---|
| 3487 | class="cmtt-8">_flag]</span><span
|
|---|
| 3488 | class="cmtt-8"> =</span><span
|
|---|
| 3489 | class="cmtt-8"> read</span><span
|
|---|
| 3490 | class="cmtt-8"> one</span><span
|
|---|
| 3491 | class="cmtt-8"> bit</span></div>
|
|---|
| 3492 | <!--l. 62--><p class="noindent" ><span
|
|---|
| 3493 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3494 | class="cmtt-12">_version] </span>is to read ’0’ in order to be compatible with this document. Both
|
|---|
| 3495 | <span
|
|---|
| 3496 | class="cmtt-12">[audio</span><span
|
|---|
| 3497 | class="cmtt-12">_channels] </span>and <span
|
|---|
| 3498 | class="cmtt-12">[audio</span><span
|
|---|
| 3499 | class="cmtt-12">_sample</span><span
|
|---|
| 3500 | class="cmtt-12">_rate] </span>must read greater than zero. Allowed final
|
|---|
| 3501 | blocksize values are 64, 128, 256, 512, 1024, 2048, 4096 and 8192 in Vorbis I. <span
|
|---|
| 3502 | class="cmtt-12">[blocksize</span><span
|
|---|
| 3503 | class="cmtt-12">_0]</span>
|
|---|
| 3504 | must be less than or equal to <span
|
|---|
| 3505 | class="cmtt-12">[blocksize</span><span
|
|---|
| 3506 | class="cmtt-12">_1]</span>. The framing bit must be nonzero. Failure to meet
|
|---|
| 3507 | any of these conditions renders a stream undecodable.
|
|---|
| 3508 | <!--l. 70--><p class="noindent" >The bitrate fields above are used only as hints. The nominal bitrate field especially may be
|
|---|
| 3509 | considerably off in purely VBR streams. The fields are meaningful only when greater than
|
|---|
| 3510 | zero.
|
|---|
| 3511 | <ul class="itemize1">
|
|---|
| 3512 | <li class="itemize">All three fields set to the same value implies a fixed rate, or tightly bounded, nearly
|
|---|
| 3513 | fixed-rate bitstream
|
|---|
| 3514 | </li>
|
|---|
| 3515 | <li class="itemize">Only nominal set implies a VBR or ABR stream that averages the nominal bitrate
|
|---|
| 3516 | </li>
|
|---|
| 3517 | <li class="itemize">Maximum and or minimum set implies a VBR bitstream that obeys the bitrate limits
|
|---|
| 3518 | </li>
|
|---|
| 3519 | <li class="itemize">None set indicates the encoder does not care to speculate.</li></ul>
|
|---|
| 3520 |
|
|---|
| 3521 |
|
|---|
| 3522 |
|
|---|
| 3523 | <!--l. 84--><p class="noindent" >
|
|---|
| 3524 | <h5 class="subsubsectionHead"><span class="titlemark">4.2.3. </span> <a
|
|---|
| 3525 | id="x1-640004.2.3"></a>Comment header</h5>
|
|---|
| 3526 | <!--l. 85--><p class="noindent" >Comment header decode and data specification is covered in <a
|
|---|
| 3527 | href="#x1-820005">section 5</a>, “<a
|
|---|
| 3528 | href="#x1-820005">comment field and
|
|---|
| 3529 | header specification<!--tex4ht:ref: vorbis:spec:comment --></a>”.
|
|---|
| 3530 | <!--l. 89--><p class="noindent" >
|
|---|
| 3531 | <h5 class="subsubsectionHead"><span class="titlemark">4.2.4. </span> <a
|
|---|
| 3532 | id="x1-650004.2.4"></a>Setup header</h5>
|
|---|
| 3533 | <!--l. 91--><p class="noindent" >Vorbis codec setup is configurable to an extreme degree:
|
|---|
| 3534 | <div class="center"
|
|---|
| 3535 | >
|
|---|
| 3536 | <!--l. 93--><p class="noindent" >
|
|---|
| 3537 |
|
|---|
| 3538 | <!--l. 94--><p class="noindent" ><img
|
|---|
| 3539 | src="components.png" alt="PIC"
|
|---|
| 3540 | >
|
|---|
| 3541 | <br /> <div class="caption"
|
|---|
| 3542 | ><span class="id">Figure 6: </span><span
|
|---|
| 3543 | class="content">decoder pipeline configuration</span></div><!--tex4ht:label?: x1-650016 -->
|
|---|
| 3544 | </div>
|
|---|
| 3545 | <!--l. 99--><p class="noindent" >The setup header contains the bulk of the codec setup information needed for decode. The setup
|
|---|
| 3546 | header contains, in order, the lists of codebook configurations, time-domain transform
|
|---|
| 3547 | configurations (placeholders in Vorbis I), floor configurations, residue configurations, channel
|
|---|
| 3548 | mapping configurations and mode configurations. It finishes with a framing bit of ’1’. Header
|
|---|
| 3549 | decode proceeds in the following order:
|
|---|
| 3550 | <!--l. 107--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 3551 | id="x1-660004.2.4"></a><span
|
|---|
| 3552 | class="cmbx-12">Codebooks</span></span>
|
|---|
| 3553 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3554 | 1. </dt><dd
|
|---|
| 3555 | class="enumerate-enumitem"><span
|
|---|
| 3556 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3557 | class="cmtt-12">_codebook</span><span
|
|---|
| 3558 | class="cmtt-12">_count] </span>= read eight bits as unsigned integer and add one
|
|---|
| 3559 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3560 | 2. </dt><dd
|
|---|
| 3561 | class="enumerate-enumitem">Decode <span
|
|---|
| 3562 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3563 | class="cmtt-12">_codebook</span><span
|
|---|
| 3564 | class="cmtt-12">_count] </span>codebooks in order as defined in <a
|
|---|
| 3565 | href="#x1-470003">section 3</a>,
|
|---|
| 3566 | “<a
|
|---|
| 3567 | href="#x1-470003">Probability Model and Codebooks<!--tex4ht:ref: vorbis:spec:codebook --></a>”. Save each configuration, in order, in an array
|
|---|
| 3568 | of codebook configurations <span
|
|---|
| 3569 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3570 | class="cmtt-12">_codebook</span><span
|
|---|
| 3571 | class="cmtt-12">_configurations]</span>.</dd></dl>
|
|---|
| 3572 |
|
|---|
| 3573 |
|
|---|
| 3574 |
|
|---|
| 3575 | <!--l. 119--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 3576 | id="x1-670004.2.4"></a><span
|
|---|
| 3577 | class="cmbx-12">Time domain transforms</span></span>
|
|---|
| 3578 | These hooks are placeholders in Vorbis I. Nevertheless, the configuration placeholder values must
|
|---|
| 3579 | be read to maintain bitstream sync.
|
|---|
| 3580 | <!--l. 126--><p class="noindent" >
|
|---|
| 3581 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3582 | 1. </dt><dd
|
|---|
| 3583 | class="enumerate-enumitem"><span
|
|---|
| 3584 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3585 | class="cmtt-12">_time</span><span
|
|---|
| 3586 | class="cmtt-12">_count] </span>= read 6 bits as unsigned integer and add one
|
|---|
| 3587 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3588 | 2. </dt><dd
|
|---|
| 3589 | class="enumerate-enumitem">read <span
|
|---|
| 3590 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3591 | class="cmtt-12">_time</span><span
|
|---|
| 3592 | class="cmtt-12">_count] </span>16 bit values; each value should be zero. If any value is
|
|---|
| 3593 | nonzero, this is an error condition and the stream is undecodable.</dd></dl>
|
|---|
| 3594 | <!--l. 132--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 3595 | id="x1-680004.2.4"></a><span
|
|---|
| 3596 | class="cmbx-12">Floors</span></span>
|
|---|
| 3597 | Vorbis uses two floor types; header decode is handed to the decode abstraction of the appropriate
|
|---|
| 3598 | type.
|
|---|
| 3599 | <!--l. 138--><p class="noindent" >
|
|---|
| 3600 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3601 | 1. </dt><dd
|
|---|
| 3602 | class="enumerate-enumitem"><span
|
|---|
| 3603 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3604 | class="cmtt-12">_floor</span><span
|
|---|
| 3605 | class="cmtt-12">_count] </span>= read 6 bits as unsigned integer and add one
|
|---|
| 3606 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3607 | 2. </dt><dd
|
|---|
| 3608 | class="enumerate-enumitem">For each <span
|
|---|
| 3609 | class="cmtt-12">[i] </span>of <span
|
|---|
| 3610 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3611 | class="cmtt-12">_floor</span><span
|
|---|
| 3612 | class="cmtt-12">_count] </span>floor numbers:
|
|---|
| 3613 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3614 | a) </dt><dd
|
|---|
| 3615 | class="enumerate-enumitem">read the floor type: vector <span
|
|---|
| 3616 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3617 | class="cmtt-12">_floor</span><span
|
|---|
| 3618 | class="cmtt-12">_types] </span>element <span
|
|---|
| 3619 | class="cmtt-12">[i] </span>= read 16 bits
|
|---|
| 3620 | as unsigned integer
|
|---|
| 3621 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3622 | b) </dt><dd
|
|---|
| 3623 | class="enumerate-enumitem">If the floor type is zero, decode the floor configuration as defined in <a
|
|---|
| 3624 | href="#x1-900006">section 6</a>,
|
|---|
| 3625 | “<a
|
|---|
| 3626 | href="#x1-900006">Floor type 0 setup and decode<!--tex4ht:ref: vorbis:spec:floor0 --></a>”; save this configuration in slot <span
|
|---|
| 3627 | class="cmtt-12">[i] </span>of the floor
|
|---|
| 3628 | configuration array <span
|
|---|
| 3629 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3630 | class="cmtt-12">_floor</span><span
|
|---|
| 3631 | class="cmtt-12">_configurations]</span>.
|
|---|
| 3632 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3633 | c) </dt><dd
|
|---|
| 3634 | class="enumerate-enumitem">If the floor type is one, decode the floor configuration as defined in <a
|
|---|
| 3635 | href="#x1-970007">section 7</a>,
|
|---|
| 3636 | “<a
|
|---|
| 3637 | href="#x1-970007">Floor type 1 setup and decode<!--tex4ht:ref: vorbis:spec:floor1 --></a>”; save this configuration in slot <span
|
|---|
| 3638 | class="cmtt-12">[i] </span>of the floor
|
|---|
| 3639 | configuration array <span
|
|---|
| 3640 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3641 | class="cmtt-12">_floor</span><span
|
|---|
| 3642 | class="cmtt-12">_configurations]</span>.
|
|---|
| 3643 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3644 | d) </dt><dd
|
|---|
| 3645 | class="enumerate-enumitem">If the the floor type is greater than one, this stream is undecodable; ERROR
|
|---|
| 3646 | CONDITION</dd></dl>
|
|---|
| 3647 |
|
|---|
| 3648 |
|
|---|
| 3649 |
|
|---|
| 3650 | </dd></dl>
|
|---|
| 3651 | <!--l. 156--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 3652 | id="x1-690004.2.4"></a><span
|
|---|
| 3653 | class="cmbx-12">Residues</span></span>
|
|---|
| 3654 | Vorbis uses three residue types; header decode of each type is identical.
|
|---|
| 3655 | <!--l. 162--><p class="noindent" >
|
|---|
| 3656 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3657 | 1. </dt><dd
|
|---|
| 3658 | class="enumerate-enumitem"><span
|
|---|
| 3659 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3660 | class="cmtt-12">_residue</span><span
|
|---|
| 3661 | class="cmtt-12">_count] </span>= read 6 bits as unsigned integer and add one
|
|---|
| 3662 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3663 | 2. </dt><dd
|
|---|
| 3664 | class="enumerate-enumitem">For each of <span
|
|---|
| 3665 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3666 | class="cmtt-12">_residue</span><span
|
|---|
| 3667 | class="cmtt-12">_count] </span>residue numbers:
|
|---|
| 3668 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3669 | a) </dt><dd
|
|---|
| 3670 | class="enumerate-enumitem">read the residue type; vector <span
|
|---|
| 3671 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3672 | class="cmtt-12">_residue</span><span
|
|---|
| 3673 | class="cmtt-12">_types] </span>element <span
|
|---|
| 3674 | class="cmtt-12">[i] </span>= read 16
|
|---|
| 3675 | bits as unsigned integer
|
|---|
| 3676 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3677 | b) </dt><dd
|
|---|
| 3678 | class="enumerate-enumitem">If the residue type is zero, one or two, decode the residue configuration as defined
|
|---|
| 3679 | in <a
|
|---|
| 3680 | href="#x1-1040008">section 8</a>, “<a
|
|---|
| 3681 | href="#x1-1040008">Residue setup and decode<!--tex4ht:ref: vorbis:spec:residue --></a>”; save this configuration in slot <span
|
|---|
| 3682 | class="cmtt-12">[i] </span>of
|
|---|
| 3683 | the residue configuration array <span
|
|---|
| 3684 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3685 | class="cmtt-12">_residue</span><span
|
|---|
| 3686 | class="cmtt-12">_configurations]</span>.
|
|---|
| 3687 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3688 | c) </dt><dd
|
|---|
| 3689 | class="enumerate-enumitem">If the the residue type is greater than two, this stream is undecodable; ERROR
|
|---|
| 3690 | CONDITION</dd></dl>
|
|---|
| 3691 | </dd></dl>
|
|---|
| 3692 | <!--l. 176--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 3693 | id="x1-700004.2.4"></a><span
|
|---|
| 3694 | class="cmbx-12">Mappings</span></span>
|
|---|
| 3695 | Mappings are used to set up specific pipelines for encoding multichannel audio with varying
|
|---|
| 3696 | channel mapping applications. Vorbis I uses a single mapping type (0), with implicit PCM
|
|---|
| 3697 | channel mappings.
|
|---|
| 3698 | <!--l. 187--><p class="noindent" >
|
|---|
| 3699 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3700 | 1. </dt><dd
|
|---|
| 3701 | class="enumerate-enumitem"><span
|
|---|
| 3702 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3703 | class="cmtt-12">_mapping</span><span
|
|---|
| 3704 | class="cmtt-12">_count] </span>= read 6 bits as unsigned integer and add one
|
|---|
| 3705 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3706 | 2. </dt><dd
|
|---|
| 3707 | class="enumerate-enumitem">For each <span
|
|---|
| 3708 | class="cmtt-12">[i] </span>of <span
|
|---|
| 3709 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3710 | class="cmtt-12">_mapping</span><span
|
|---|
| 3711 | class="cmtt-12">_count] </span>mapping numbers:
|
|---|
| 3712 |
|
|---|
| 3713 |
|
|---|
| 3714 |
|
|---|
| 3715 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3716 | a) </dt><dd
|
|---|
| 3717 | class="enumerate-enumitem">read the mapping type: 16 bits as unsigned integer. There’s no reason to save
|
|---|
| 3718 | the mapping type in Vorbis I.
|
|---|
| 3719 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3720 | b) </dt><dd
|
|---|
| 3721 | class="enumerate-enumitem">If the mapping type is nonzero, the stream is undecodable
|
|---|
| 3722 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3723 | c) </dt><dd
|
|---|
| 3724 | class="enumerate-enumitem">If the mapping type is zero:
|
|---|
| 3725 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3726 | i. </dt><dd
|
|---|
| 3727 | class="enumerate-enumitem">read 1 bit as a boolean flag
|
|---|
| 3728 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3729 | A. </dt><dd
|
|---|
| 3730 | class="enumerate-enumitem">if set, <span
|
|---|
| 3731 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3732 | class="cmtt-12">_mapping</span><span
|
|---|
| 3733 | class="cmtt-12">_submaps] </span>= read 4 bits as unsigned integer
|
|---|
| 3734 | and add one
|
|---|
| 3735 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3736 | B. </dt><dd
|
|---|
| 3737 | class="enumerate-enumitem">if unset, <span
|
|---|
| 3738 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3739 | class="cmtt-12">_mapping</span><span
|
|---|
| 3740 | class="cmtt-12">_submaps] </span>= 1</dd></dl>
|
|---|
| 3741 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3742 | ii. </dt><dd
|
|---|
| 3743 | class="enumerate-enumitem">read 1 bit as a boolean flag
|
|---|
| 3744 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3745 | A. </dt><dd
|
|---|
| 3746 | class="enumerate-enumitem">if set, square polar channel mapping is in use:
|
|---|
| 3747 | <ul class="itemize1">
|
|---|
| 3748 | <li class="itemize"><span
|
|---|
| 3749 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3750 | class="cmtt-12">_mapping</span><span
|
|---|
| 3751 | class="cmtt-12">_coupling</span><span
|
|---|
| 3752 | class="cmtt-12">_steps] </span>= read 8 bits as unsigned
|
|---|
| 3753 | integer and add one
|
|---|
| 3754 | </li>
|
|---|
| 3755 | <li class="itemize">for <span
|
|---|
| 3756 | class="cmtt-12">[j] </span>each of <span
|
|---|
| 3757 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3758 | class="cmtt-12">_mapping</span><span
|
|---|
| 3759 | class="cmtt-12">_coupling</span><span
|
|---|
| 3760 | class="cmtt-12">_steps] </span>steps:
|
|---|
| 3761 | <ul class="itemize2">
|
|---|
| 3762 | <li class="itemize">vector <span
|
|---|
| 3763 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3764 | class="cmtt-12">_mapping</span><span
|
|---|
| 3765 | class="cmtt-12">_magnitude] </span>element <span
|
|---|
| 3766 | class="cmtt-12">[j]</span>= read
|
|---|
| 3767 | <a
|
|---|
| 3768 | href="#x1-1190009.2.1">ilog</a>(<span
|
|---|
| 3769 | class="cmtt-12">[audio</span><span
|
|---|
| 3770 | class="cmtt-12">_channels] </span>- 1) bits as unsigned integer
|
|---|
| 3771 | </li>
|
|---|
| 3772 | <li class="itemize">vector <span
|
|---|
| 3773 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3774 | class="cmtt-12">_mapping</span><span
|
|---|
| 3775 | class="cmtt-12">_angle] </span>element <span
|
|---|
| 3776 | class="cmtt-12">[j]</span>= read
|
|---|
| 3777 | <a
|
|---|
| 3778 | href="#x1-1190009.2.1">ilog</a>(<span
|
|---|
| 3779 | class="cmtt-12">[audio</span><span
|
|---|
| 3780 | class="cmtt-12">_channels] </span>- 1) bits as unsigned integer
|
|---|
| 3781 | </li>
|
|---|
| 3782 | <li class="itemize">the numbers read in the above two steps are channel numbers
|
|---|
| 3783 | representing the channel to treat as magnitude and the channel
|
|---|
| 3784 | to treat as angle, respectively. If for any coupling step the
|
|---|
| 3785 | angle channel number equals the magnitude channel number, the
|
|---|
| 3786 | magnitude channel number is greater than <span
|
|---|
| 3787 | class="cmtt-12">[audio</span><span
|
|---|
| 3788 | class="cmtt-12">_channels]</span>-1, or
|
|---|
| 3789 | the angle channel is greater than <span
|
|---|
| 3790 | class="cmtt-12">[audio</span><span
|
|---|
| 3791 | class="cmtt-12">_channels]</span>-1, the stream
|
|---|
| 3792 | is undecodable.</li></ul>
|
|---|
| 3793 |
|
|---|
| 3794 |
|
|---|
| 3795 |
|
|---|
| 3796 | </li></ul>
|
|---|
| 3797 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3798 | B. </dt><dd
|
|---|
| 3799 | class="enumerate-enumitem">if unset, <span
|
|---|
| 3800 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3801 | class="cmtt-12">_mapping</span><span
|
|---|
| 3802 | class="cmtt-12">_coupling</span><span
|
|---|
| 3803 | class="cmtt-12">_steps] </span>= 0</dd></dl>
|
|---|
| 3804 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3805 | iii. </dt><dd
|
|---|
| 3806 | class="enumerate-enumitem">read 2 bits (reserved field); if the value is nonzero, the stream is undecodable
|
|---|
| 3807 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3808 | iv. </dt><dd
|
|---|
| 3809 | class="enumerate-enumitem">if <span
|
|---|
| 3810 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3811 | class="cmtt-12">_mapping</span><span
|
|---|
| 3812 | class="cmtt-12">_submaps] </span>is greater than one, we read channel multiplex
|
|---|
| 3813 | settings. For each <span
|
|---|
| 3814 | class="cmtt-12">[j] </span>of <span
|
|---|
| 3815 | class="cmtt-12">[audio</span><span
|
|---|
| 3816 | class="cmtt-12">_channels] </span>channels:
|
|---|
| 3817 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3818 | A. </dt><dd
|
|---|
| 3819 | class="enumerate-enumitem">vector <span
|
|---|
| 3820 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3821 | class="cmtt-12">_mapping</span><span
|
|---|
| 3822 | class="cmtt-12">_mux] </span>element <span
|
|---|
| 3823 | class="cmtt-12">[j] </span>= read 4 bits as unsigned
|
|---|
| 3824 | integer
|
|---|
| 3825 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3826 | B. </dt><dd
|
|---|
| 3827 | class="enumerate-enumitem">if the value is greater than the highest numbered submap
|
|---|
| 3828 | (<span
|
|---|
| 3829 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3830 | class="cmtt-12">_mapping</span><span
|
|---|
| 3831 | class="cmtt-12">_submaps] </span>- 1), this in an error condition rendering
|
|---|
| 3832 | the stream undecodable</dd></dl>
|
|---|
| 3833 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3834 | v. </dt><dd
|
|---|
| 3835 | class="enumerate-enumitem">for each submap <span
|
|---|
| 3836 | class="cmtt-12">[j] </span>of <span
|
|---|
| 3837 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3838 | class="cmtt-12">_mapping</span><span
|
|---|
| 3839 | class="cmtt-12">_submaps] </span>submaps, read the floor and
|
|---|
| 3840 | residue numbers for use in decoding that submap:
|
|---|
| 3841 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3842 | A. </dt><dd
|
|---|
| 3843 | class="enumerate-enumitem">read and discard 8 bits (the unused time configuration placeholder)
|
|---|
| 3844 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3845 | B. </dt><dd
|
|---|
| 3846 | class="enumerate-enumitem">read 8 bits as unsigned integer for the floor number; save in vector
|
|---|
| 3847 | <span
|
|---|
| 3848 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3849 | class="cmtt-12">_mapping</span><span
|
|---|
| 3850 | class="cmtt-12">_submap</span><span
|
|---|
| 3851 | class="cmtt-12">_floor] </span>element <span
|
|---|
| 3852 | class="cmtt-12">[j]</span>
|
|---|
| 3853 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3854 | C. </dt><dd
|
|---|
| 3855 | class="enumerate-enumitem">verify the floor number is not greater than the highest number floor
|
|---|
| 3856 | configured for the bitstream. If it is, the bitstream is undecodable
|
|---|
| 3857 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3858 | D. </dt><dd
|
|---|
| 3859 | class="enumerate-enumitem">read 8 bits as unsigned integer for the residue number; save in vector
|
|---|
| 3860 | <span
|
|---|
| 3861 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3862 | class="cmtt-12">_mapping</span><span
|
|---|
| 3863 | class="cmtt-12">_submap</span><span
|
|---|
| 3864 | class="cmtt-12">_residue] </span>element <span
|
|---|
| 3865 | class="cmtt-12">[j]</span>
|
|---|
| 3866 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3867 | E. </dt><dd
|
|---|
| 3868 | class="enumerate-enumitem">verify the residue number is not greater than the highest number residue
|
|---|
| 3869 | configured for the bitstream. If it is, the bitstream is undecodable</dd></dl>
|
|---|
| 3870 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3871 | vi. </dt><dd
|
|---|
| 3872 | class="enumerate-enumitem">save this mapping configuration in slot <span
|
|---|
| 3873 | class="cmtt-12">[i] </span>of the mapping configuration array
|
|---|
| 3874 | <span
|
|---|
| 3875 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3876 | class="cmtt-12">_mapping</span><span
|
|---|
| 3877 | class="cmtt-12">_configurations]</span>.</dd></dl>
|
|---|
| 3878 | </dd></dl>
|
|---|
| 3879 |
|
|---|
| 3880 |
|
|---|
| 3881 |
|
|---|
| 3882 | </dd></dl>
|
|---|
| 3883 | <!--l. 246--><p class="noindent" ><span class="paragraphHead"><a
|
|---|
| 3884 | id="x1-710004.2.4"></a><span
|
|---|
| 3885 | class="cmbx-12">Modes</span></span>
|
|---|
| 3886 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3887 | 1. </dt><dd
|
|---|
| 3888 | class="enumerate-enumitem"><span
|
|---|
| 3889 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3890 | class="cmtt-12">_mode</span><span
|
|---|
| 3891 | class="cmtt-12">_count] </span>= read 6 bits as unsigned integer and add one
|
|---|
| 3892 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3893 | 2. </dt><dd
|
|---|
| 3894 | class="enumerate-enumitem">For each of <span
|
|---|
| 3895 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3896 | class="cmtt-12">_mode</span><span
|
|---|
| 3897 | class="cmtt-12">_count] </span>mode numbers:
|
|---|
| 3898 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3899 | a) </dt><dd
|
|---|
| 3900 | class="enumerate-enumitem"><span
|
|---|
| 3901 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3902 | class="cmtt-12">_mode</span><span
|
|---|
| 3903 | class="cmtt-12">_blockflag] </span>= read 1 bit
|
|---|
| 3904 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3905 | b) </dt><dd
|
|---|
| 3906 | class="enumerate-enumitem"><span
|
|---|
| 3907 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3908 | class="cmtt-12">_mode</span><span
|
|---|
| 3909 | class="cmtt-12">_windowtype] </span>= read 16 bits as unsigned integer
|
|---|
| 3910 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3911 | c) </dt><dd
|
|---|
| 3912 | class="enumerate-enumitem"><span
|
|---|
| 3913 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3914 | class="cmtt-12">_mode</span><span
|
|---|
| 3915 | class="cmtt-12">_transformtype] </span>= read 16 bits as unsigned integer
|
|---|
| 3916 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3917 | d) </dt><dd
|
|---|
| 3918 | class="enumerate-enumitem"><span
|
|---|
| 3919 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3920 | class="cmtt-12">_mode</span><span
|
|---|
| 3921 | class="cmtt-12">_mapping] </span>= read 8 bits as unsigned integer
|
|---|
| 3922 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3923 | e) </dt><dd
|
|---|
| 3924 | class="enumerate-enumitem">verify ranges; zero is the only legal value in
|
|---|
| 3925 | Vorbis I for <span
|
|---|
| 3926 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3927 | class="cmtt-12">_mode</span><span
|
|---|
| 3928 | class="cmtt-12">_windowtype] </span>and <span
|
|---|
| 3929 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3930 | class="cmtt-12">_mode</span><span
|
|---|
| 3931 | class="cmtt-12">_transformtype]</span>.
|
|---|
| 3932 | <span
|
|---|
| 3933 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3934 | class="cmtt-12">_mode</span><span
|
|---|
| 3935 | class="cmtt-12">_mapping] </span>must not be greater than the highest number mapping
|
|---|
| 3936 | in use. Any illegal values render the stream undecodable.
|
|---|
| 3937 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3938 | f) </dt><dd
|
|---|
| 3939 | class="enumerate-enumitem">save this mode configuration in slot <span
|
|---|
| 3940 | class="cmtt-12">[i] </span>of the mode configuration array
|
|---|
| 3941 | <span
|
|---|
| 3942 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3943 | class="cmtt-12">_mode</span><span
|
|---|
| 3944 | class="cmtt-12">_configurations]</span>.</dd></dl>
|
|---|
| 3945 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3946 | 3. </dt><dd
|
|---|
| 3947 | class="enumerate-enumitem">read 1 bit as a framing flag. If unset, a framing error occurred and the stream is not
|
|---|
| 3948 | decodable.</dd></dl>
|
|---|
| 3949 | <!--l. 267--><p class="noindent" >After reading mode descriptions, setup header decode is complete.
|
|---|
| 3950 | <!--l. 276--><p class="noindent" >
|
|---|
| 3951 | <h4 class="subsectionHead"><span class="titlemark">4.3. </span> <a
|
|---|
| 3952 | id="x1-720004.3"></a>Audio packet decode and synthesis</h4>
|
|---|
| 3953 |
|
|---|
| 3954 |
|
|---|
| 3955 |
|
|---|
| 3956 | <!--l. 278--><p class="noindent" >Following the three header packets, all packets in a Vorbis I stream are audio. The first step of
|
|---|
| 3957 | audio packet decode is to read and verify the packet type. <span
|
|---|
| 3958 | class="cmti-12">A non-audio packet when audio is</span>
|
|---|
| 3959 | <span
|
|---|
| 3960 | class="cmti-12">expected indicates stream corruption or a non-compliant stream. The decoder must ignore the</span>
|
|---|
| 3961 | <span
|
|---|
| 3962 | class="cmti-12">packet and not attempt decoding it to audio</span>.
|
|---|
| 3963 | <!--l. 285--><p class="noindent" >
|
|---|
| 3964 | <h5 class="subsubsectionHead"><span class="titlemark">4.3.1. </span> <a
|
|---|
| 3965 | id="x1-730004.3.1"></a>packet type, mode and window decode</h5>
|
|---|
| 3966 | <!--l. 288--><p class="noindent" >
|
|---|
| 3967 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3968 | 1. </dt><dd
|
|---|
| 3969 | class="enumerate-enumitem">read 1 bit <span
|
|---|
| 3970 | class="cmtt-12">[packet</span><span
|
|---|
| 3971 | class="cmtt-12">_type]</span>; check that packet type is 0 (audio)
|
|---|
| 3972 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3973 | 2. </dt><dd
|
|---|
| 3974 | class="enumerate-enumitem">read <a
|
|---|
| 3975 | href="#x1-1190009.2.1">ilog</a>([vorbis_mode_count]-1) bits <span
|
|---|
| 3976 | class="cmtt-12">[mode</span><span
|
|---|
| 3977 | class="cmtt-12">_number]</span>
|
|---|
| 3978 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3979 | 3. </dt><dd
|
|---|
| 3980 | class="enumerate-enumitem">decode blocksize <span
|
|---|
| 3981 | class="cmtt-12">[n] </span>is equal to <span
|
|---|
| 3982 | class="cmtt-12">[blocksize</span><span
|
|---|
| 3983 | class="cmtt-12">_0] </span>if <span
|
|---|
| 3984 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3985 | class="cmtt-12">_mode</span><span
|
|---|
| 3986 | class="cmtt-12">_blockflag] </span>is 0,
|
|---|
| 3987 | else <span
|
|---|
| 3988 | class="cmtt-12">[n] </span>is equal to <span
|
|---|
| 3989 | class="cmtt-12">[blocksize</span><span
|
|---|
| 3990 | class="cmtt-12">_1]</span>.
|
|---|
| 3991 | </dd><dt class="enumerate-enumitem">
|
|---|
| 3992 | 4. </dt><dd
|
|---|
| 3993 | class="enumerate-enumitem">perform window selection and setup; this window is used later by the inverse
|
|---|
| 3994 | MDCT:
|
|---|
| 3995 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 3996 | a) </dt><dd
|
|---|
| 3997 | class="enumerate-enumitem">if this is a long window (the <span
|
|---|
| 3998 | class="cmtt-12">[vorbis</span><span
|
|---|
| 3999 | class="cmtt-12">_mode</span><span
|
|---|
| 4000 | class="cmtt-12">_blockflag] </span>flag of this mode is
|
|---|
| 4001 | set):
|
|---|
| 4002 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4003 | i. </dt><dd
|
|---|
| 4004 | class="enumerate-enumitem">read 1 bit for <span
|
|---|
| 4005 | class="cmtt-12">[previous</span><span
|
|---|
| 4006 | class="cmtt-12">_window</span><span
|
|---|
| 4007 | class="cmtt-12">_flag]</span>
|
|---|
| 4008 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4009 | ii. </dt><dd
|
|---|
| 4010 | class="enumerate-enumitem">read 1 bit for <span
|
|---|
| 4011 | class="cmtt-12">[next</span><span
|
|---|
| 4012 | class="cmtt-12">_window</span><span
|
|---|
| 4013 | class="cmtt-12">_flag]</span>
|
|---|
| 4014 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4015 | iii. </dt><dd
|
|---|
| 4016 | class="enumerate-enumitem">if <span
|
|---|
| 4017 | class="cmtt-12">[previous</span><span
|
|---|
| 4018 | class="cmtt-12">_window</span><span
|
|---|
| 4019 | class="cmtt-12">_flag] </span>is not set, the left half of the window will
|
|---|
| 4020 | be a hybrid window for lapping with a short block. See <a
|
|---|
| 4021 | href="#paragraph.1" >paragraph <a
|
|---|
| 4022 | href="#x1-260001.3.2">1.3.2</a></a>,
|
|---|
| 4023 | “<a
|
|---|
| 4024 | href="#x1-260001.3.2">Window shape decode (long windows only)<!--tex4ht:ref: vorbis:spec:window --></a>” for an illustration of
|
|---|
| 4025 | overlapping dissimilar windows. Else, the left half window will have normal
|
|---|
| 4026 | long shape.
|
|---|
| 4027 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4028 | iv. </dt><dd
|
|---|
| 4029 | class="enumerate-enumitem">if <span
|
|---|
| 4030 | class="cmtt-12">[next</span><span
|
|---|
| 4031 | class="cmtt-12">_window</span><span
|
|---|
| 4032 | class="cmtt-12">_flag] </span>is not set, the right half of the window will be
|
|---|
| 4033 | a hybrid window for lapping with a short block. See <a
|
|---|
| 4034 | href="#x1-260001.3.2">paragraph 1.3.2</a>,
|
|---|
| 4035 |
|
|---|
| 4036 |
|
|---|
| 4037 |
|
|---|
| 4038 | “<a
|
|---|
| 4039 | href="#x1-260001.3.2">Window shape decode (long windows only)<!--tex4ht:ref: vorbis:spec:window --></a>” for an illustration of
|
|---|
| 4040 | overlapping dissimilar windows. Else, the left right window will have normal
|
|---|
| 4041 | long shape.</dd></dl>
|
|---|
| 4042 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4043 | b) </dt><dd
|
|---|
| 4044 | class="enumerate-enumitem">if this is a short window, the window is always the same short-window
|
|---|
| 4045 | shape.</dd></dl>
|
|---|
| 4046 | </dd></dl>
|
|---|
| 4047 | <!--l. 320--><p class="noindent" >Vorbis windows all use the slope function <span
|
|---|
| 4048 | class="cmmi-12">y </span>= sin(<img
|
|---|
| 4049 | src="Vorbis_I_spec1x.png" alt="π
|
|---|
| 4050 | 2" class="frac" align="middle"> <span
|
|---|
| 4051 | class="cmsy-10x-x-120">*</span> sin <sup><span
|
|---|
| 4052 | class="cmr-8">2</span></sup>((<span
|
|---|
| 4053 | class="cmmi-12">x </span>+ 0<span
|
|---|
| 4054 | class="cmmi-12">.</span>5)<span
|
|---|
| 4055 | class="cmmi-12">∕n </span><span
|
|---|
| 4056 | class="cmsy-10x-x-120">* </span><span
|
|---|
| 4057 | class="cmmi-12">π</span>)), where <span
|
|---|
| 4058 | class="cmmi-12">n </span>is window
|
|---|
| 4059 | size and <span
|
|---|
| 4060 | class="cmmi-12">x </span>ranges 0<span
|
|---|
| 4061 | class="cmmi-12">…</span><span
|
|---|
| 4062 | class="cmmi-12">n</span><span
|
|---|
| 4063 | class="cmsy-10x-x-120">- </span>1, but dissimilar lapping requirements can affect overall shape. Window
|
|---|
| 4064 | generation proceeds as follows:
|
|---|
| 4065 | <!--l. 326--><p class="noindent" >
|
|---|
| 4066 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4067 | 1. </dt><dd
|
|---|
| 4068 | class="enumerate-enumitem"><span
|
|---|
| 4069 | class="cmtt-12">[window</span><span
|
|---|
| 4070 | class="cmtt-12">_center] </span>= <span
|
|---|
| 4071 | class="cmtt-12">[n] </span>/ 2
|
|---|
| 4072 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4073 | 2. </dt><dd
|
|---|
| 4074 | class="enumerate-enumitem">if (<span
|
|---|
| 4075 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4076 | class="cmtt-12">_mode</span><span
|
|---|
| 4077 | class="cmtt-12">_blockflag] </span>is set and <span
|
|---|
| 4078 | class="cmtt-12">[previous</span><span
|
|---|
| 4079 | class="cmtt-12">_window</span><span
|
|---|
| 4080 | class="cmtt-12">_flag] </span>is not set)
|
|---|
| 4081 | then
|
|---|
| 4082 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4083 | a) </dt><dd
|
|---|
| 4084 | class="enumerate-enumitem"><span
|
|---|
| 4085 | class="cmtt-12">[left</span><span
|
|---|
| 4086 | class="cmtt-12">_window</span><span
|
|---|
| 4087 | class="cmtt-12">_start] </span>= <span
|
|---|
| 4088 | class="cmtt-12">[n]</span>/4 - <span
|
|---|
| 4089 | class="cmtt-12">[blocksize</span><span
|
|---|
| 4090 | class="cmtt-12">_0]</span>/4
|
|---|
| 4091 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4092 | b) </dt><dd
|
|---|
| 4093 | class="enumerate-enumitem"><span
|
|---|
| 4094 | class="cmtt-12">[left</span><span
|
|---|
| 4095 | class="cmtt-12">_window</span><span
|
|---|
| 4096 | class="cmtt-12">_end] </span>= <span
|
|---|
| 4097 | class="cmtt-12">[n]</span>/4 + <span
|
|---|
| 4098 | class="cmtt-12">[blocksize</span><span
|
|---|
| 4099 | class="cmtt-12">_0]</span>/4
|
|---|
| 4100 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4101 | c) </dt><dd
|
|---|
| 4102 | class="enumerate-enumitem"><span
|
|---|
| 4103 | class="cmtt-12">[left</span><span
|
|---|
| 4104 | class="cmtt-12">_n] </span>= <span
|
|---|
| 4105 | class="cmtt-12">[blocksize</span><span
|
|---|
| 4106 | class="cmtt-12">_0]</span>/2</dd></dl>
|
|---|
| 4107 | <!--l. 335--><p class="noindent" >else
|
|---|
| 4108 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4109 | a) </dt><dd
|
|---|
| 4110 | class="enumerate-enumitem"><span
|
|---|
| 4111 | class="cmtt-12">[left</span><span
|
|---|
| 4112 | class="cmtt-12">_window</span><span
|
|---|
| 4113 | class="cmtt-12">_start] </span>= 0
|
|---|
| 4114 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4115 | b) </dt><dd
|
|---|
| 4116 | class="enumerate-enumitem"><span
|
|---|
| 4117 | class="cmtt-12">[left</span><span
|
|---|
| 4118 | class="cmtt-12">_window</span><span
|
|---|
| 4119 | class="cmtt-12">_end] </span>= <span
|
|---|
| 4120 | class="cmtt-12">[window</span><span
|
|---|
| 4121 | class="cmtt-12">_center]</span>
|
|---|
| 4122 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4123 | c) </dt><dd
|
|---|
| 4124 | class="enumerate-enumitem"><span
|
|---|
| 4125 | class="cmtt-12">[left</span><span
|
|---|
| 4126 | class="cmtt-12">_n] </span>= <span
|
|---|
| 4127 | class="cmtt-12">[n]</span>/2</dd></dl>
|
|---|
| 4128 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4129 | 3. </dt><dd
|
|---|
| 4130 | class="enumerate-enumitem">if (<span
|
|---|
| 4131 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4132 | class="cmtt-12">_mode</span><span
|
|---|
| 4133 | class="cmtt-12">_blockflag] </span>is set and <span
|
|---|
| 4134 | class="cmtt-12">[next</span><span
|
|---|
| 4135 | class="cmtt-12">_window</span><span
|
|---|
| 4136 | class="cmtt-12">_flag] </span>is not set) then
|
|---|
| 4137 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4138 | a) </dt><dd
|
|---|
| 4139 | class="enumerate-enumitem"><span
|
|---|
| 4140 | class="cmtt-12">[right</span><span
|
|---|
| 4141 | class="cmtt-12">_window</span><span
|
|---|
| 4142 | class="cmtt-12">_start] </span>= <span
|
|---|
| 4143 | class="cmtt-12">[n]*3</span>/4 - <span
|
|---|
| 4144 | class="cmtt-12">[blocksize</span><span
|
|---|
| 4145 | class="cmtt-12">_0]</span>/4
|
|---|
| 4146 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4147 | b) </dt><dd
|
|---|
| 4148 | class="enumerate-enumitem"><span
|
|---|
| 4149 | class="cmtt-12">[right</span><span
|
|---|
| 4150 | class="cmtt-12">_window</span><span
|
|---|
| 4151 | class="cmtt-12">_end] </span>= <span
|
|---|
| 4152 | class="cmtt-12">[n]*3</span>/4 + <span
|
|---|
| 4153 | class="cmtt-12">[blocksize</span><span
|
|---|
| 4154 | class="cmtt-12">_0]</span>/4
|
|---|
| 4155 |
|
|---|
| 4156 |
|
|---|
| 4157 |
|
|---|
| 4158 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4159 | c) </dt><dd
|
|---|
| 4160 | class="enumerate-enumitem"><span
|
|---|
| 4161 | class="cmtt-12">[right</span><span
|
|---|
| 4162 | class="cmtt-12">_n] </span>= <span
|
|---|
| 4163 | class="cmtt-12">[blocksize</span><span
|
|---|
| 4164 | class="cmtt-12">_0]</span>/2</dd></dl>
|
|---|
| 4165 | <!--l. 351--><p class="noindent" >else
|
|---|
| 4166 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4167 | a) </dt><dd
|
|---|
| 4168 | class="enumerate-enumitem"><span
|
|---|
| 4169 | class="cmtt-12">[right</span><span
|
|---|
| 4170 | class="cmtt-12">_window</span><span
|
|---|
| 4171 | class="cmtt-12">_start] </span>= <span
|
|---|
| 4172 | class="cmtt-12">[window</span><span
|
|---|
| 4173 | class="cmtt-12">_center]</span>
|
|---|
| 4174 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4175 | b) </dt><dd
|
|---|
| 4176 | class="enumerate-enumitem"><span
|
|---|
| 4177 | class="cmtt-12">[right</span><span
|
|---|
| 4178 | class="cmtt-12">_window</span><span
|
|---|
| 4179 | class="cmtt-12">_end] </span>= <span
|
|---|
| 4180 | class="cmtt-12">[n]</span>
|
|---|
| 4181 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4182 | c) </dt><dd
|
|---|
| 4183 | class="enumerate-enumitem"><span
|
|---|
| 4184 | class="cmtt-12">[right</span><span
|
|---|
| 4185 | class="cmtt-12">_n] </span>= <span
|
|---|
| 4186 | class="cmtt-12">[n]</span>/2</dd></dl>
|
|---|
| 4187 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4188 | 4. </dt><dd
|
|---|
| 4189 | class="enumerate-enumitem">window from range 0 ... <span
|
|---|
| 4190 | class="cmtt-12">[left</span><span
|
|---|
| 4191 | class="cmtt-12">_window</span><span
|
|---|
| 4192 | class="cmtt-12">_start]</span>-1 inclusive is zero
|
|---|
| 4193 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4194 | 5. </dt><dd
|
|---|
| 4195 | class="enumerate-enumitem">for <span
|
|---|
| 4196 | class="cmtt-12">[i] </span>in range <span
|
|---|
| 4197 | class="cmtt-12">[left</span><span
|
|---|
| 4198 | class="cmtt-12">_window</span><span
|
|---|
| 4199 | class="cmtt-12">_start] </span>... <span
|
|---|
| 4200 | class="cmtt-12">[left</span><span
|
|---|
| 4201 | class="cmtt-12">_window</span><span
|
|---|
| 4202 | class="cmtt-12">_end]</span>-1, window(<span
|
|---|
| 4203 | class="cmtt-12">[i]</span>) =
|
|---|
| 4204 | sin(<img
|
|---|
| 4205 | src="Vorbis_I_spec2x.png" alt="π
|
|---|
| 4206 | 2" class="frac" align="middle"> <span
|
|---|
| 4207 | class="cmsy-10x-x-120">*</span> sin <sup><span
|
|---|
| 4208 | class="cmr-8">2</span></sup>( (<span
|
|---|
| 4209 | class="cmtt-12">[i]</span>-<span
|
|---|
| 4210 | class="cmtt-12">[left</span><span
|
|---|
| 4211 | class="cmtt-12">_window</span><span
|
|---|
| 4212 | class="cmtt-12">_start]</span>+0.5) / <span
|
|---|
| 4213 | class="cmtt-12">[left</span><span
|
|---|
| 4214 | class="cmtt-12">_n] </span><span
|
|---|
| 4215 | class="cmsy-10x-x-120">*</span><img
|
|---|
| 4216 | src="Vorbis_I_spec3x.png" alt="π
|
|---|
| 4217 | 2" class="frac" align="middle">) )
|
|---|
| 4218 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4219 | 6. </dt><dd
|
|---|
| 4220 | class="enumerate-enumitem">window from range <span
|
|---|
| 4221 | class="cmtt-12">[left</span><span
|
|---|
| 4222 | class="cmtt-12">_window</span><span
|
|---|
| 4223 | class="cmtt-12">_end] </span>... <span
|
|---|
| 4224 | class="cmtt-12">[right</span><span
|
|---|
| 4225 | class="cmtt-12">_window</span><span
|
|---|
| 4226 | class="cmtt-12">_start]</span>-1 inclusive is
|
|---|
| 4227 | one
|
|---|
| 4228 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4229 | 7. </dt><dd
|
|---|
| 4230 | class="enumerate-enumitem">for <span
|
|---|
| 4231 | class="cmtt-12">[i] </span>in range <span
|
|---|
| 4232 | class="cmtt-12">[right</span><span
|
|---|
| 4233 | class="cmtt-12">_window</span><span
|
|---|
| 4234 | class="cmtt-12">_start] </span>... <span
|
|---|
| 4235 | class="cmtt-12">[right</span><span
|
|---|
| 4236 | class="cmtt-12">_window</span><span
|
|---|
| 4237 | class="cmtt-12">_end]</span>-1, window(<span
|
|---|
| 4238 | class="cmtt-12">[i]</span>) =
|
|---|
| 4239 | sin(<img
|
|---|
| 4240 | src="Vorbis_I_spec4x.png" alt="π2" class="frac" align="middle"> <span
|
|---|
| 4241 | class="cmsy-10x-x-120">*</span> sin <sup><span
|
|---|
| 4242 | class="cmr-8">2</span></sup>( (<span
|
|---|
| 4243 | class="cmtt-12">[i]</span>-<span
|
|---|
| 4244 | class="cmtt-12">[right</span><span
|
|---|
| 4245 | class="cmtt-12">_window</span><span
|
|---|
| 4246 | class="cmtt-12">_start]</span>+0.5) / <span
|
|---|
| 4247 | class="cmtt-12">[right</span><span
|
|---|
| 4248 | class="cmtt-12">_n] </span><span
|
|---|
| 4249 | class="cmsy-10x-x-120">*</span><img
|
|---|
| 4250 | src="Vorbis_I_spec5x.png" alt="π2" class="frac" align="middle"> + <img
|
|---|
| 4251 | src="Vorbis_I_spec6x.png" alt="π2" class="frac" align="middle">) )
|
|---|
| 4252 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4253 | 8. </dt><dd
|
|---|
| 4254 | class="enumerate-enumitem">window from range <span
|
|---|
| 4255 | class="cmtt-12">[right</span><span
|
|---|
| 4256 | class="cmtt-12">_window</span><span
|
|---|
| 4257 | class="cmtt-12">_start] </span>... <span
|
|---|
| 4258 | class="cmtt-12">[n]</span>-1 is zero</dd></dl>
|
|---|
| 4259 | <!--l. 367--><p class="noindent" >An end-of-packet condition up to this point should be considered an error that discards this
|
|---|
| 4260 | packet from the stream. An end of packet condition past this point is to be considered a possible
|
|---|
| 4261 | nominal occurrence.
|
|---|
| 4262 | <!--l. 374--><p class="noindent" >
|
|---|
| 4263 | <h5 class="subsubsectionHead"><span class="titlemark">4.3.2. </span> <a
|
|---|
| 4264 | id="x1-740004.3.2"></a>floor curve decode</h5>
|
|---|
| 4265 | <!--l. 376--><p class="noindent" >From this point on, we assume out decode context is using mode number <span
|
|---|
| 4266 | class="cmtt-12">[mode</span><span
|
|---|
| 4267 | class="cmtt-12">_number]</span>
|
|---|
| 4268 | from configuration array <span
|
|---|
| 4269 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4270 | class="cmtt-12">_mode</span><span
|
|---|
| 4271 | class="cmtt-12">_configurations] </span>and the map number
|
|---|
| 4272 | <span
|
|---|
| 4273 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4274 | class="cmtt-12">_mode</span><span
|
|---|
| 4275 | class="cmtt-12">_mapping] </span>(specified by the current mode) taken from the mapping configuration
|
|---|
| 4276 | array <span
|
|---|
| 4277 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4278 | class="cmtt-12">_mapping</span><span
|
|---|
| 4279 | class="cmtt-12">_configurations]</span>.
|
|---|
| 4280 | <!--l. 383--><p class="noindent" >Floor curves are decoded one-by-one in channel order.
|
|---|
| 4281 |
|
|---|
| 4282 |
|
|---|
| 4283 |
|
|---|
| 4284 | <!--l. 385--><p class="noindent" >For each floor <span
|
|---|
| 4285 | class="cmtt-12">[i] </span>of <span
|
|---|
| 4286 | class="cmtt-12">[audio</span><span
|
|---|
| 4287 | class="cmtt-12">_channels]</span>
|
|---|
| 4288 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4289 | 1. </dt><dd
|
|---|
| 4290 | class="enumerate-enumitem"><span
|
|---|
| 4291 | class="cmtt-12">[submap</span><span
|
|---|
| 4292 | class="cmtt-12">_number] </span>= element <span
|
|---|
| 4293 | class="cmtt-12">[i] </span>of vector [vorbis_mapping_mux]
|
|---|
| 4294 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4295 | 2. </dt><dd
|
|---|
| 4296 | class="enumerate-enumitem"><span
|
|---|
| 4297 | class="cmtt-12">[floor</span><span
|
|---|
| 4298 | class="cmtt-12">_number] </span>= element <span
|
|---|
| 4299 | class="cmtt-12">[submap</span><span
|
|---|
| 4300 | class="cmtt-12">_number] </span>of vector [vorbis_submap_floor]
|
|---|
| 4301 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4302 | 3. </dt><dd
|
|---|
| 4303 | class="enumerate-enumitem">if the floor type of this floor (vector
|
|---|
| 4304 | <span
|
|---|
| 4305 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4306 | class="cmtt-12">_floor</span><span
|
|---|
| 4307 | class="cmtt-12">_types] </span>element <span
|
|---|
| 4308 | class="cmtt-12">[floor</span><span
|
|---|
| 4309 | class="cmtt-12">_number]</span>) is zero then decode the floor for
|
|---|
| 4310 | channel <span
|
|---|
| 4311 | class="cmtt-12">[i] </span>according to the <a
|
|---|
| 4312 | href="#x1-940006.2.2">subsubsection 6.2.2</a>, “<a
|
|---|
| 4313 | href="#x1-940006.2.2">packet decode<!--tex4ht:ref: vorbis:spec:floor0-decode --></a>”
|
|---|
| 4314 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4315 | 4. </dt><dd
|
|---|
| 4316 | class="enumerate-enumitem">if the type of this floor is one then decode the floor for channel <span
|
|---|
| 4317 | class="cmtt-12">[i] </span>according to the
|
|---|
| 4318 | <a
|
|---|
| 4319 | href="#x1-1020007.2.3">subsubsection 7.2.3</a>, “<a
|
|---|
| 4320 | href="#x1-1020007.2.3">packet decode<!--tex4ht:ref: vorbis:spec:floor1-decode --></a>”
|
|---|
| 4321 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4322 | 5. </dt><dd
|
|---|
| 4323 | class="enumerate-enumitem">save the needed decoded floor information for channel for later synthesis
|
|---|
| 4324 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4325 | 6. </dt><dd
|
|---|
| 4326 | class="enumerate-enumitem">if the decoded floor returned ’unused’, set vector <span
|
|---|
| 4327 | class="cmtt-12">[no</span><span
|
|---|
| 4328 | class="cmtt-12">_residue] </span>element <span
|
|---|
| 4329 | class="cmtt-12">[i] </span>to true,
|
|---|
| 4330 | else set vector <span
|
|---|
| 4331 | class="cmtt-12">[no</span><span
|
|---|
| 4332 | class="cmtt-12">_residue] </span>element <span
|
|---|
| 4333 | class="cmtt-12">[i] </span>to false</dd></dl>
|
|---|
| 4334 | <!--l. 405--><p class="noindent" >An end-of-packet condition during floor decode shall result in packet decode zeroing all channel
|
|---|
| 4335 | output vectors and skipping to the add/overlap output stage.
|
|---|
| 4336 | <!--l. 411--><p class="noindent" >
|
|---|
| 4337 | <h5 class="subsubsectionHead"><span class="titlemark">4.3.3. </span> <a
|
|---|
| 4338 | id="x1-750004.3.3"></a>nonzero vector propagate</h5>
|
|---|
| 4339 | <!--l. 413--><p class="noindent" >A possible result of floor decode is that a specific vector is marked ’unused’ which indicates that
|
|---|
| 4340 | that final output vector is all-zero values (and the floor is zero). The residue for that vector is not
|
|---|
| 4341 | coded in the stream, save for one complication. If some vectors are used and some are not,
|
|---|
| 4342 | channel coupling could result in mixing a zeroed and nonzeroed vector to produce two nonzeroed
|
|---|
| 4343 | vectors.
|
|---|
| 4344 | <!--l. 420--><p class="noindent" >for each <span
|
|---|
| 4345 | class="cmtt-12">[i] </span>from 0 ... <span
|
|---|
| 4346 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4347 | class="cmtt-12">_mapping</span><span
|
|---|
| 4348 | class="cmtt-12">_coupling</span><span
|
|---|
| 4349 | class="cmtt-12">_steps]</span>-1
|
|---|
| 4350 | <!--l. 423--><p class="noindent" >
|
|---|
| 4351 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4352 | 1. </dt><dd
|
|---|
| 4353 | class="enumerate-enumitem">if either <span
|
|---|
| 4354 | class="cmtt-12">[no</span><span
|
|---|
| 4355 | class="cmtt-12">_residue] </span>entry for channel (<span
|
|---|
| 4356 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4357 | class="cmtt-12">_mapping</span><span
|
|---|
| 4358 | class="cmtt-12">_magnitude] </span>element
|
|---|
| 4359 | <span
|
|---|
| 4360 | class="cmtt-12">[i]</span>) or channel (<span
|
|---|
| 4361 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4362 | class="cmtt-12">_mapping</span><span
|
|---|
| 4363 | class="cmtt-12">_angle] </span>element <span
|
|---|
| 4364 | class="cmtt-12">[i]</span>) are set to false, then both
|
|---|
| 4365 | must be set to false. Note that an ’unused’ floor has no decoded floor information; it
|
|---|
| 4366 |
|
|---|
| 4367 |
|
|---|
| 4368 |
|
|---|
| 4369 | is important that this is remembered at floor curve synthesis time.</dd></dl>
|
|---|
| 4370 | <!--l. 435--><p class="noindent" >
|
|---|
| 4371 | <h5 class="subsubsectionHead"><span class="titlemark">4.3.4. </span> <a
|
|---|
| 4372 | id="x1-760004.3.4"></a>residue decode</h5>
|
|---|
| 4373 | <!--l. 437--><p class="noindent" >Unlike floors, which are decoded in channel order, the residue vectors are decoded in submap
|
|---|
| 4374 | order.
|
|---|
| 4375 | <!--l. 440--><p class="noindent" >for each submap <span
|
|---|
| 4376 | class="cmtt-12">[i] </span>in order from 0 ... <span
|
|---|
| 4377 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4378 | class="cmtt-12">_mapping</span><span
|
|---|
| 4379 | class="cmtt-12">_submaps]</span>-1
|
|---|
| 4380 | <!--l. 443--><p class="noindent" >
|
|---|
| 4381 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4382 | 1. </dt><dd
|
|---|
| 4383 | class="enumerate-enumitem"><span
|
|---|
| 4384 | class="cmtt-12">[ch] </span>= 0
|
|---|
| 4385 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4386 | 2. </dt><dd
|
|---|
| 4387 | class="enumerate-enumitem">for each channel <span
|
|---|
| 4388 | class="cmtt-12">[j] </span>in order from 0 ... <span
|
|---|
| 4389 | class="cmtt-12">[audio</span><span
|
|---|
| 4390 | class="cmtt-12">_channels] </span>- 1
|
|---|
| 4391 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4392 | a) </dt><dd
|
|---|
| 4393 | class="enumerate-enumitem">if channel <span
|
|---|
| 4394 | class="cmtt-12">[j] </span>in submap <span
|
|---|
| 4395 | class="cmtt-12">[i] </span>(vector <span
|
|---|
| 4396 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4397 | class="cmtt-12">_mapping</span><span
|
|---|
| 4398 | class="cmtt-12">_mux] </span>element <span
|
|---|
| 4399 | class="cmtt-12">[j] </span>is equal to
|
|---|
| 4400 | <span
|
|---|
| 4401 | class="cmtt-12">[i]</span>)
|
|---|
| 4402 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4403 | i. </dt><dd
|
|---|
| 4404 | class="enumerate-enumitem">if vector <span
|
|---|
| 4405 | class="cmtt-12">[no</span><span
|
|---|
| 4406 | class="cmtt-12">_residue] </span>element <span
|
|---|
| 4407 | class="cmtt-12">[j] </span>is true
|
|---|
| 4408 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4409 | A. </dt><dd
|
|---|
| 4410 | class="enumerate-enumitem">vector <span
|
|---|
| 4411 | class="cmtt-12">[do</span><span
|
|---|
| 4412 | class="cmtt-12">_not</span><span
|
|---|
| 4413 | class="cmtt-12">_decode</span><span
|
|---|
| 4414 | class="cmtt-12">_flag] </span>element <span
|
|---|
| 4415 | class="cmtt-12">[ch] </span>is set</dd></dl>
|
|---|
| 4416 | <!--l. 452--><p class="noindent" >else
|
|---|
| 4417 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4418 | A. </dt><dd
|
|---|
| 4419 | class="enumerate-enumitem">vector <span
|
|---|
| 4420 | class="cmtt-12">[do</span><span
|
|---|
| 4421 | class="cmtt-12">_not</span><span
|
|---|
| 4422 | class="cmtt-12">_decode</span><span
|
|---|
| 4423 | class="cmtt-12">_flag] </span>element <span
|
|---|
| 4424 | class="cmtt-12">[ch] </span>is unset</dd></dl>
|
|---|
| 4425 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4426 | ii. </dt><dd
|
|---|
| 4427 | class="enumerate-enumitem">increment <span
|
|---|
| 4428 | class="cmtt-12">[ch]</span></dd></dl>
|
|---|
| 4429 | </dd></dl>
|
|---|
| 4430 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4431 | 3. </dt><dd
|
|---|
| 4432 | class="enumerate-enumitem"><span
|
|---|
| 4433 | class="cmtt-12">[residue</span><span
|
|---|
| 4434 | class="cmtt-12">_number] </span>= vector <span
|
|---|
| 4435 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4436 | class="cmtt-12">_mapping</span><span
|
|---|
| 4437 | class="cmtt-12">_submap</span><span
|
|---|
| 4438 | class="cmtt-12">_residue] </span>element <span
|
|---|
| 4439 | class="cmtt-12">[i]</span>
|
|---|
| 4440 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4441 | 4. </dt><dd
|
|---|
| 4442 | class="enumerate-enumitem"><span
|
|---|
| 4443 | class="cmtt-12">[residue</span><span
|
|---|
| 4444 | class="cmtt-12">_type] </span>= vector <span
|
|---|
| 4445 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4446 | class="cmtt-12">_residue</span><span
|
|---|
| 4447 | class="cmtt-12">_types] </span>element <span
|
|---|
| 4448 | class="cmtt-12">[residue</span><span
|
|---|
| 4449 | class="cmtt-12">_number]</span>
|
|---|
| 4450 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4451 | 5. </dt><dd
|
|---|
| 4452 | class="enumerate-enumitem">decode <span
|
|---|
| 4453 | class="cmtt-12">[ch] </span>vectors using residue <span
|
|---|
| 4454 | class="cmtt-12">[residue</span><span
|
|---|
| 4455 | class="cmtt-12">_number]</span>, according to type <span
|
|---|
| 4456 | class="cmtt-12">[residue</span><span
|
|---|
| 4457 | class="cmtt-12">_type]</span>,
|
|---|
| 4458 |
|
|---|
| 4459 |
|
|---|
| 4460 |
|
|---|
| 4461 | also passing vector <span
|
|---|
| 4462 | class="cmtt-12">[do</span><span
|
|---|
| 4463 | class="cmtt-12">_not</span><span
|
|---|
| 4464 | class="cmtt-12">_decode</span><span
|
|---|
| 4465 | class="cmtt-12">_flag] </span>to indicate which vectors in the bundle should
|
|---|
| 4466 | not be decoded. Correct per-vector decode length is <span
|
|---|
| 4467 | class="cmtt-12">[n]</span>/2.
|
|---|
| 4468 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4469 | 6. </dt><dd
|
|---|
| 4470 | class="enumerate-enumitem"><span
|
|---|
| 4471 | class="cmtt-12">[ch] </span>= 0
|
|---|
| 4472 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4473 | 7. </dt><dd
|
|---|
| 4474 | class="enumerate-enumitem">for each channel <span
|
|---|
| 4475 | class="cmtt-12">[j] </span>in order from 0 ... <span
|
|---|
| 4476 | class="cmtt-12">[audio</span><span
|
|---|
| 4477 | class="cmtt-12">_channels]</span>
|
|---|
| 4478 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4479 | a) </dt><dd
|
|---|
| 4480 | class="enumerate-enumitem">if channel <span
|
|---|
| 4481 | class="cmtt-12">[j] </span>is in submap <span
|
|---|
| 4482 | class="cmtt-12">[i] </span>(vector <span
|
|---|
| 4483 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4484 | class="cmtt-12">_mapping</span><span
|
|---|
| 4485 | class="cmtt-12">_mux] </span>element <span
|
|---|
| 4486 | class="cmtt-12">[j] </span>is equal
|
|---|
| 4487 | to <span
|
|---|
| 4488 | class="cmtt-12">[i]</span>)
|
|---|
| 4489 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4490 | i. </dt><dd
|
|---|
| 4491 | class="enumerate-enumitem">residue vector for channel <span
|
|---|
| 4492 | class="cmtt-12">[j] </span>is set to decoded residue vector <span
|
|---|
| 4493 | class="cmtt-12">[ch]</span>
|
|---|
| 4494 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4495 | ii. </dt><dd
|
|---|
| 4496 | class="enumerate-enumitem">increment <span
|
|---|
| 4497 | class="cmtt-12">[ch]</span></dd></dl>
|
|---|
| 4498 | </dd></dl>
|
|---|
| 4499 | </dd></dl>
|
|---|
| 4500 | <!--l. 479--><p class="noindent" >
|
|---|
| 4501 | <h5 class="subsubsectionHead"><span class="titlemark">4.3.5. </span> <a
|
|---|
| 4502 | id="x1-770004.3.5"></a>inverse coupling</h5>
|
|---|
| 4503 | <!--l. 481--><p class="noindent" >for each <span
|
|---|
| 4504 | class="cmtt-12">[i] </span>from <span
|
|---|
| 4505 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4506 | class="cmtt-12">_mapping</span><span
|
|---|
| 4507 | class="cmtt-12">_coupling</span><span
|
|---|
| 4508 | class="cmtt-12">_steps]</span>-1 descending to 0
|
|---|
| 4509 | <!--l. 484--><p class="noindent" >
|
|---|
| 4510 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4511 | 1. </dt><dd
|
|---|
| 4512 | class="enumerate-enumitem"><span
|
|---|
| 4513 | class="cmtt-12">[magnitude</span><span
|
|---|
| 4514 | class="cmtt-12">_vector] </span>= the residue vector for channel (vector
|
|---|
| 4515 | <span
|
|---|
| 4516 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4517 | class="cmtt-12">_mapping</span><span
|
|---|
| 4518 | class="cmtt-12">_magnitude] </span>element <span
|
|---|
| 4519 | class="cmtt-12">[i]</span>)
|
|---|
| 4520 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4521 | 2. </dt><dd
|
|---|
| 4522 | class="enumerate-enumitem"><span
|
|---|
| 4523 | class="cmtt-12">[angle</span><span
|
|---|
| 4524 | class="cmtt-12">_vector] </span>= the residue vector for channel (vector <span
|
|---|
| 4525 | class="cmtt-12">[vorbis</span><span
|
|---|
| 4526 | class="cmtt-12">_mapping</span><span
|
|---|
| 4527 | class="cmtt-12">_angle]</span>
|
|---|
| 4528 | element <span
|
|---|
| 4529 | class="cmtt-12">[i]</span>)
|
|---|
| 4530 | </dd><dt class="enumerate-enumitem">
|
|---|
| 4531 | 3. </dt><dd
|
|---|
| 4532 | class="enumerate-enumitem">for each scalar value <span
|
|---|
| 4533 | class="cmtt-12">[M] </span>in vector <span
|
|---|
| 4534 | class="cmtt-12">[magnitude</span><span
|
|---|
| 4535 | class="cmtt-12">_vector] </span>and the corresponding scalar value
|
|---|
| 4536 | <span
|
|---|
| 4537 | class="cmtt-12">[A] </span>in vector <span
|
|---|
| 4538 | class="cmtt-12">[angle</span><span
|
|---|
| 4539 | class="cmtt-12">_vector]</span>:
|
|---|
| 4540 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4541 | a) </dt><dd
|
|---|
| 4542 | class="enumerate-enumitem">if (<span
|
|---|
| 4543 | class="cmtt-12">[M] </span>is greater than zero)
|
|---|
| 4544 |
|
|---|
| 4545 |
|
|---|
| 4546 |
|
|---|
| 4547 | <dl class="enumerate-enumitem"><dt class="enumerate-enumitem">
|
|---|
| 4548 | i. </dt><dd
|
|---|
| 4549 | class="enumerate-enumitem">if (<span
|
|---|
| 4550 | class="cmtt-12">[A] </span>is greater than zero)
|
|---|
| 4551 | <dl class="enumerate-enumitem& |
|---|
