On 01/14/2014 04:47 PM, Alexander E. Patrakov wrote:
> In my opinion (if this counts at all), this needs to be fixed in
> PulseAudio, and not only because of your hardware. Indeed, the
> SND_PCM_NO_AUTO_CHANNELS_{UP,DOWN} solution proposed by David would
> "work" for you, but it is suboptimal, because it would no longer talk
> to the "hw" devices (as it could if it added the empty channels
> itself). Talking to mmapped "hw" devices is, if I understand
> correctly, a necessary condition for timestamp-based scheduling, which
> is beneficial for applications. Due to the same reason, and again if I
> understand correctly, timestamp-based scheduling is currently
> unavailable for sound cards that rely on the route plugin in their
> ALSA configs. It would be nice to get rid of this suboptimal thing,
> too, by implementing the equivalent functionality inside PulseAudio.
PulseAudio can use timer scheduling even when mmap is disabled. Besides,
IIRC all of the plug, route and volume alsa plugins use mmap emulation,
so PulseAudio sees it as a mmaped device anyway.
However, the performance argument is correct, and valid, as alsa-lib
will end up converting samples without PulseAudio knowing about it.
--
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic
