Index: /trunk/src/VBox/Main/src-client/DrvAudioVideoRec.cpp
===================================================================
--- /trunk/src/VBox/Main/src-client/DrvAudioVideoRec.cpp	(revision 74847)
+++ /trunk/src/VBox/Main/src-client/DrvAudioVideoRec.cpp	(revision 74848)
@@ -324,4 +324,16 @@
 
         LogRel(("VideoRec: Audio codec failed to set bitrate (%RU32): %s\n", uBitrate, opus_strerror(orc)));
+        return VERR_AUDIO_BACKEND_INIT_FAILED;
+    }
+
+    const bool fUseVBR = true; /** Use Variable Bit Rate (VBR) by default. @todo Make this configurable? */
+
+    orc = opus_encoder_ctl(pEnc, OPUS_SET_VBR(fUseVBR ? 1 : 0));
+    if (orc != OPUS_OK)
+    {
+        opus_encoder_destroy(pEnc);
+        pEnc = NULL;
+
+        LogRel(("VideoRec: Audio codec failed to %s VBR mode: %s\n", fUseVBR ? "enable" : "disable", opus_strerror(orc)));
         return VERR_AUDIO_BACKEND_INIT_FAILED;
     }