[alsa-devel] PulseAudio and softvol
arun.raghavan at collabora.co.uk
Wed Jun 26 08:59:31 CEST 2013
On Thu, 2013-05-16 at 08:31 +0200, David Henningsson wrote:
> On 05/15/2013 06:28 PM, Takashi Iwai wrote:
> > Yes, but the invocation of PCM softvol isn't guaranteed to be first
> > before the reference to the already existing user ctl element.
> > snd_mixer_open() can be called before that.
> So this is a transient problem, right? As soon as the first PCM is
> opened, the TLV would be corrected, and then stay corrected for all
> times to come.
> And looking at the current PulseAudio code, it does open the pcm device
> before it opens the mixer/ctl device.
> So, if this isn't possible to solve in a better way, maybe we need to be
> pragmatic about it - PulseAudio is the only application we know that
> would care, and it opens the pcm device first. So in practice, it looks
> like the TLV approach would work.
> > The very reason we'd like to filter out the mixer control created by
> > softvol is that this mixer element confuses PA as if it actually
> > changes the volume (e.g. "PCM") although PA ignores the softvol. If
Actually, we don't currently ignore softvol. I guess we could add the
no-softvol flag once we're able to make sure we don't have any softvol
> > user creates PCM volume in alsaloop in a different fashion as PA
> > expected, the similar problem may happen. How can we detect this
> > logically...? In other words, how can PA adjust the mixer elements
> > for alsaloop properly?
> So if alsaloop is run, only once, that could cause a control to be added
> for all future, due to alsactl saving and restoring it?
> If so, that looks like a problem with alsaloop. If it adds controls, it
> should also remove them.
> If no, I don't think we need to worry. Alsaloop is probably mostly used
> on non-PA systems (as PA has module-loopback which does the same thing).
Seems this thread died out. I didn't quite understand the
alsaloop/alsactl-specific concerns, tbh. What do we need to do to take
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