[Spice-devel] [PATCH] make celt to be optional

[Alon Levy]

On Fri, Jun 15, 2012 at 11:17:34AM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > From 44.1 you'd still need to externally resample to one of 8, 12, 16, 24,
> > or 48k - but you can put any of those rates in, and take any of those out
> > again without them needing to be the same.  So only endpoints actually
> > needing an 'oddball' rate would need a resampler to get them, they wouldn't
> > force the other end to also support and use that rate as well.
> 
> Ok, so we must resample 44.1 anyway before encoding.
> 
> >> Is that true for celt 0.5.1 too btw?
> > 
> > Unfortunately no.  For celt you compose your own 'mode' and that mode
> > essentially defines the bitstream.  Different modes make different
> > bitstreams so you need to decode with the same mode you encoded with.
> 
> Ok, so it's easiest to simply not touch celt.
> 
> So, how to go forward?  spice-server gets a 44.1 stream from qemu today.
>  I think we should switch that to 48k.  Needs changes in the sound
> interface and in qemu.  spice-server needs to be able to handle both old
> (44.1) and new (48k) qemu.  spice-server also needs to be able to handle
> clients with different capabilities (possibly even at the same time if
> multiclient is enabled, not sure multiclient support covers the sound
> channel though).

No sound channel for multiclient.

> 
> So we'll need resampling support for both 44.1 -> 48k and 48k -> 44.1.
> In the end we'll have the following cases, at the server side:
> 
>   old qemu, no caps [-> 44.1 pcm]
>   pass through pcm audio data as-is
> 
>   new qemu, no caps [-> 44.1 pcm]
>   resample 48k -> 44.1
> 
>   old qemu, cap_celt
>   encode 44.1 celt
> 
>   new qemu, cap_celt
>   resample 48k -> 44.1, encode 44.1 celt
> 
>   old qemu, cap_opus
>   resample 44.1 -> 48k, encode opus
> 
>   new qemu, cap_opus
>   encode opus
> 
> We might want to add:
> 
>   new qemu, cap_pcm48k
>   pass through pcm audio data as-is
> 
> Long-term (new spice-server, new qemu, clients supporting opus) we'll
> operate at 48k on the whole chain without resampling needed in the
> spice-server.
> 
> Client side is easy, we just decode stuff and pass it on to pulseaudio
> to deal with it.
> 

Sounds like a good plan.

> cheers,
>   Gerd
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