[pulseaudio-discuss] Suggestions on how to support avoid-resampling on PulseEffects

[Arun Raghavan]

On Sun, 23 Sep 2018, at 6:57 AM, wellington wallace wrote:
> On Sat, Sep 22, 2018 at 9:17 PM Arun Raghavan <arun at arunraghavan.net> wrote:
> 
> >
> >
> > On Sat, 22 Sep 2018, at 10:03 PM, wellington wallace wrote:
> > > Hi PA developers!
> > >
> > > As you can see here https://github.com/wwmm/pulseeffects/issues/288
> > there
> > > are users that would like to have avoid-resampling supported in
> > > PulseEffects(and I would like it too). But honestly I am out of good
> > ideas
> > > about how to do this. At this moment I am using null sinks to do the
> > audio
> > > routing and there is a Gstreamer pipeline that records from it. I can
> > > change the format and rate of the GStreamer pipiline to the ones used by
> > > the audio application being processed but as I can't do the same to the
> > > null sink it would be pointless. The resampling would happen anyway.
> > >
> > > At this moment the only way I see to support avoid-resampling would be to
> > > reload the null sink with the new rate and format. But this is really
> > > annoying because as soon as I kill the null sink Pulseaudio will move the
> > > audio application back to the default device. It is not impossible to
> > deal
> > > with this. But it may require major changes in the code.
> > >
> > > Is reloading the null sink the only way to deal with this? It crossed my
> > > mind to try to make a custom null sink that could change these parameters
> > > on the fly. But besides the fact that Arch Linux packages do not have
> > > Pulseaudio developement headers I don't even know if it is possible to
> > make
> > > any null sink that would accept this.
> >
> > I have patches in the queue to enable reconfiguration for
> > module-null-sink.
> > https://gitlab.freedesktop.org/pulseaudio/pulseaudio/merge_requests/14
> >
> > Should be easy enough to add a modarg like we have for ALSA to make it
> > also just request support at module load time.
> >
> > -- Arun
> >
> 
> Hi Arun! These are very good news! So is the null sink going to
> automatically update its rate like it happens with the sound card sink when
> avoid-resampling is enabled? Or will it be necessary to take action using
> the libpulse api? Based on what I could understand of alsa-sink code it
> seems the first option. Assuming this to be the case is the sampling rate
> update going to trigger the "sink changed" event?
> 
> An automatic reconfiguration would welcome. This way I can focus only on
> the GStreamer pipeline and I wouldn't have different code paths for
> different Pulseaudio versions.

It's the latter. I don't think we emit a sink-changed, but we should.

Cheers,
Arun