[pulseaudio-discuss] Supporting hardware resampling

Mark Brown broonie at sirena.org.uk
Tue Nov 30 05:09:48 PST 2010

On Tue, Nov 30, 2010 at 12:44:45PM +0000, Colin Guthrie wrote:

> In theory you'd want to group all the same-freq data together, mix it
> and then pass it to the sink which would use the DSP to do the
> resampling needed, which isn't really something supported right now in
> the PA architecture AFAIK.

With the links you've got to most DSPs you don't actually need to do the
pre-mixing - the DSP can do the mixing too.

> The trick comes from knowing the h/w can do this. I guess one way of
> working would be to change things so that each sink can actually open
> the h/w multiple times for different sample rates if it supports h/w
> mixing and simply route the audio to the appropriate connection, all the
> while maintaining a single sink "view" to all things higher up.

For things like the emu10k based cards simply opening the PCM until you
get an error should do the job here.

> It's likely something that will be attached in some way to the UCM work
> in alsa, so that this kind of thing is only configured when we are told
> it will work.

This would work for OMAP.  The other thing that Pulse should be able to
use eventually is Laurent Pinchard's media controller work which will
allow Pulse to discover the audio routing within the device.  Probably
that will cover most of the PC cases.

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