VRDP audio forwarding broken on Windows 10 RDP client

[Radu Dan]

Hey,

My host is a NAS-like CentOS 6 box with no attached monitor, no X server and no sound card. On it I spawn a bunch of lightweight bridged Windows machines for browser testing and connect to them from my desktop PC running Windows (gigabit LAN between the client and server).

This setup worked flawlessly with Virtualbox 4.3 and Windows 8.1. I've stopped using the VMs for a while and recently ressurected them with the following changes:

• Updated to Virtualbox 5
• Switched desktop to Windows 10

Since I did that, I'm getting choppy high pitched audio when connecting to the VMs (both before and after installing guest additions). The emulated chipset is Intel HDA and the driver is obviously Null as the host doesn't have a sound card. I originally thought this was an emulation issue, however:

• after doing some research about other issues about windows 10 clients being unable to connect in previous versions
• and reading on some other oracle website that VRDP only supports 22050 audio (not explicitly related to vbox, but pretty sure the V stands for the same thing),

I believe the issue is strictly related to the changes in the Windows 10 RDP client because:

1. playing back a realtime 22050hz stream on a 44100 output device would explain both symptoms (high pitch caused by the freq mismatch and choppiness caused by buffer underrun)
2. setting up a windows RDP server on a guest (tested on a win10 guest) and connecting to that works flawlessly

Unfortunately, I don't have a Windows 7 box to test this on, but I'm going to try some RDP-ception later today.

[Radu Dan]

Okay, I can confirm this now. It's going to get a bit messy, so bare with me.

We're going to be working with 4 machines:

• My win10 desktop, going to call this one Observer (O)
• A CentOS 6 linux NAS that's running Virtualbox 5.0.12 (H)
• A win7 guest VM on the linux host (7)
• A win10 guest VM on the linux host (10)

7 and 10 each have two RDP servers:

• A VRDP server running on the linux host (let's call those 7V and 10V)
• A MS-RDP server running on the guests themselves (let's call those 7M and 10M)

Since the guests are bridged, all machines show up on the same network and can talk to each other directly.

My tests are as follows:

1. RDP from O to 7M and expect the audio to work properly
2. RDP from O to 7M to 10V and expect the audio to work properly
3. RDP from O to 10M and expect the audio to work properly
4. RDP from O to 10M to 7V and expect the audio to be choppy and high pitched

What I can say for certain is that performance issues aside, my tests pass so I can now experimentally confirm my previous belief. This is definitely a RDP-server issue.

[virt_user_2]

This issue also affects me (​https://forums.virtualbox.org/viewtopic.php?f=2&t=74893)

[virt_user_2]

Workaround:

Install Virtual Box on the windows machine, then create a linux guest that can run rdesktop. This is way too convoluted and an inefficient use of resources, but it works.