Re: [Qemu-devel] QEMU VNC Audio - All audio data null

[agraham <agraham@g-b.net>]

On 07/14/2012 11:44 AM, malc wrote:
> On Sat, 14 Jul 2012, agraham wrote:
>
>> On 07/14/2012 03:17 AM, agraham wrote:
>>> Hi Guys,
>>>
>>> I've written a VNC client that implements the VNC QEMU Audio extensions.
>>> Using QEMU 0.13 it works very very for remote sound, however after
>>> upgrading to QEMU 1.1.0 the audio stream contains only bytes of zeros,
>>> so this results in no sound on the client.
>>>
>>> It is almost like the stream is muted by sending 0 bytes instead of the
>>> actual data.
>>>
>>> 0: VNC: :SOUND: AudioOn
>>> 1: VNC: :SOUND: Received _QEMU_Audio_Server_Message: Operation: 1
>>> 2: VNC: :SOUND: Received _QEMU_Audio_Start
>>> 3: VNC: :SOUND: Received _QEMU_Audio_Server_Message: Operation: 2
>>> 4: VNC: :SOUND: Received _QEMU_Audio_Data 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
>>> 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
>>>
>>> Is there something new that needs to be done in order for the sound to
>>> be pushed out, like some unmute mechanism?
>>>
>>> I rebuilt QEMU 0.15.1 and sound worked but was very choppy, I think due
>>> to some timer injection changes - but that's another issue.
>>>
>>> Thanks in advance.
>>>
>>> Albert
>>
>> I've just rebuilt QEMU 1.0 (and all of its dependencies) and it has the same
>> problem (zero bytes), so some incompatibility was introduced between 0.15.1
>> and 1.1.0.
>>
>> Anyone got any clues ?
>
> Please try to bisect the issue.
>

My previous comment had a typo, it should have said: between 0.15.1 and 
1.0. (not 1.1.0)

bi-section so far:

I suspect that one of the following patches is causing the issue, these 
are all added to QEMU 1.0 (by Fedora at least) and are included in 1.1.0 
upstream.

# Spice volume control backports, all are upstream for 1.1
Patch501: 0501-audio-add-VOICE_VOLUME-ctl.patch
Patch502: 0502-audio-don-t-apply-volume-effect-if-backend-has-VOICE.patch
Patch503: 0503-hw-ac97-remove-USE_MIXER-code.patch
Patch504: 0504-hw-ac97-the-volume-mask-is-not-only-0x1f.patch
Patch505: 0505-hw-ac97-add-support-for-volume-control.patch
Patch506: 0506-audio-spice-add-support-for-volume-control.patch
Patch507: 0507-Do-not-use-pa_simple-PulseAudio-API.patch
Patch508: 0508-configure-pa_simple-is-not-needed-anymore.patch
Patch509: 0509-Allow-controlling-volume-with-PulseAudio-backend.patch

In order to use the QEMU VNC Audio for remote sound, you must
export QEMU_AUDIO_DRV=none, this indicates that you are not using a 
back-end.

QEMU_AUDIO_DRV=none is deceptive, but accurate, it tells QEMU not to 
connect to the QEMU host sound system. It does _not_ mean there is no sound.

Volume/mute control for VNC QEMU remote sound should _always_ be managed 
from the client side and should be on by default, but it looks like 
something is interfering with the stream from QEMU >0.15.1 on the server 
side and thus breaking the QEMU VNC extension.

Albert