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

[Gerd Hoffmann]

On 11/10/10 12:50, Daniel P. Berrange wrote:
> On Wed, Nov 10, 2010 at 12:37:04PM +0100, Gerd Hoffmann wrote:
> > 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.

Well, on a standard fedora install alsa ends up being routed to 
pulseaudio anyway.  Not sure what happens with SDL, I suspect it goes 
via alsa to pulseaudio too.

So I've bothered with pulseaudio (and spice) only in my testing.
Came up with these patches for pulseaudio:

  http://cgit.freedesktop.org/spice/qemu/log/?h=pulse

These patches make pulseaudio work alot better for me.
They are waiting to be reviewed by Fengguang right now.

> Just testing with mpg123 in the guest, audio
> will often simply stop after a few seconds of playback to the
> host.

Fedora 14 + rhythmbox works rock solid for me.

Win7 + media player works too but has dropouts now and then, I think 
this is because win7 uses a very small dma buffer for the audio data.  I 
don't see the sound stopping altogether.

> 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.

Naturally I'm testing with the new intel-hda device ;)

It has some advantages, for example it just got MSI support so it 
doesn't has to share the IRQ line with other devices (when the guest 
supports it).  I think there is nothing which makes a major difference 
compared to ac97.  I don't know ac97 that well though.

cheers,
  Gerd