Re: [Qemu-devel] Re: [PATCH] spice: add audio

[Daniel P. Berrange]

On Wed, Nov 10, 2010 at 12:37:04PM +0100, Gerd Hoffmann wrote:
> On 11/10/10 11:36, Daniel P. Berrange wrote:
> >On Wed, Nov 10, 2010 at 10:48:39AM +0100, Gerd Hoffmann wrote:
> >>The qemu vnc server has support already, and I think Daniel (added to
> >>Cc:) has some experimental patches for the gtk-vnc widget.
> >
> >Yes I do have patches, but I'm yet to get it to work reliably enough for
> >anyone to use for real. eg any time there are large frambuffer updates
> >due to, say, dragging a window around, audio will drop out.  Until I can
> >prove that it is even semi-reliable I'm not going to include the code in
> >gtk-vnc, because I don't want to commit to supporting something that may
> >well be fundamentally broken/unusable for live audio playback.
> 
> Do you know where the dropouts come from?

Not entirely, it is still rather work in progress to debug it.
Part of the issues is that even QEMU + one of the standard
pulseaudio/alsa/sdl audio backends doesn't seem very reliable
to me, so I've not got a reliable benchmark to compare VNC 
audio against. Just testing with mpg123 in the guest, audio
will often simply stop after a few seconds of playback to the
host.

> I think one issue are latencies within qemu.  The qemu vnc server is 
> busy for a while when doing bulky screen updates and blocks other stuff 
> while it runs.  I've seen dropouts with vnc + bulky screen updates too. 
> The smaller the audio buffers used by the device/guest are the more 
> visible this effect is.  When enabling the threaded vnc server this 
> becomes alot better, did you try that?

It looks like the threaded server is disabled by default, so I've
not been using it thus far. I'll give it a try though.

Is there a particular audio device that is considered to work 'best' ?
I've been using ac97 mostly, but if your new ICH6 device is thought
to be significantly better I'll try that instead.

Regards,
Daniel
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