[pulseaudio-discuss] [PATCH] sink, source: Add a mode to avoid resampling if possible

[Tanu Kaskinen]

On Sun, 2017-01-29 at 23:23 +0530, Arun Raghavan wrote:
> 
> On Sun, 29 Jan 2017, at 02:29 PM, Tanu Kaskinen wrote:
> > On Sun, 2017-01-29 at 10:29 +0530, Arun Raghavan wrote:
> > > This adds an "avoid-resampling" option to daemon.conf that makes the
> > > daemon try to use the stream sample rate if possible (the device needs
> > > to support it, which currently only ALSA does), and there should not be
> > > any other stream connected).
> > > 
> > > This should enable some of the "audiophile" use-cases where users wish
> > > to play high sample rate audio files without resampling.
> > > 
> > > We still will do conversion if sample formats don't match, though. This
> > > means that if you want to play 96 kHz/24 bit audio without any
> > > modification the default format will need to be set to be 24-bit as
> > > well. This will force all streams to be upconverted, which, other than
> > > the wasted resources, should be relatively harmless.
> > > ---
> > >  man/pulse-daemon.conf.5.xml.in |  9 +++++++++
> > >  src/daemon/daemon-conf.c       |  3 +++
> > >  src/daemon/daemon-conf.h       |  1 +
> > >  src/daemon/daemon.conf.in      |  1 +
> > >  src/daemon/main.c              |  1 +
> > >  src/pulsecore/core.h           |  1 +
> > >  src/pulsecore/sink.c           | 10 ++++++++--
> > >  src/pulsecore/source.c         |  9 +++++++--
> > >  8 files changed, 31 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/man/pulse-daemon.conf.5.xml.in b/man/pulse-daemon.conf.5.xml.in
> > > index b81a549..cb09b97 100644
> > > --- a/man/pulse-daemon.conf.5.xml.in
> > > +++ b/man/pulse-daemon.conf.5.xml.in
> > > @@ -124,6 +124,15 @@ License along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
> > >      </option>
> > >  
> > >      <option>
> > > +      <p><opt>avoid-resampling=</opt> If set, try to configure the
> > > +      device to avoid resampling. This only works if on devices that
> > 
> > The extra "if" is still here.
> > 
> > > @@ -1442,7 +1443,12 @@ int pa_sink_update_rate(pa_sink *s, uint32_t rate, bool passthrough) {
> > >      if (PA_UNLIKELY(!pa_sample_rate_valid(desired_rate)))
> > >          return -1;
> > >  
> > > -    if (!passthrough && default_rate != desired_rate && alternate_rate != desired_rate) {
> > > +    if (avoid_resampling && (rate >= default_rate || rate >= alternate_rate)) {
> > > +        /* We just try to set the sink input's sample rate if it's not too low */
> > > +        if (rate > default_rate || rate > alternate_rate)
> > > +            desired_rate = rate;
> > 
> > Now the code works, which is nice. However, you said that the
> 
> I don't know what you're talking about. It was working before, this
> makes the condition cause the alternate resample rate calculation to be
> used in the case of avoid_resampling=true and the desired rate being too
> low. .

I meant that your original patch didn't do what you intended it to do.
I believe your intention was to not allow the sink rate to be changed
to a value smaller than default_rate or alternate_rate, but the
original patch did allow that.

> > "desired_rate = rate" assignment makes the code clearer, but I
> > disagree. The code looks like the intention is to do something if the
> > "rate > default_rate || rate > alternate_rate" condition is true, but
> > actually the code never does anything, regardless of whether the
> > condition is true or false.
> 
> That part was wrong, the second if was a duplicate (I fixed it in
> source.c but not sink.c).

Ok, I didn't notice that source.c was different. (BTW, the indentation
in source.c is off.)

> > If you think leaving the code block empty or merging the "if" and "else
> > if" branches makes the code unclear, then I think a comment is more
> > appropriate way to clarify things than adding code that doesn't do
> > anything.
> 
> I'm not sure I understand -- are you saying the code in source.c is
> fine, or that it needs to not do anything in the avoid_resampling case
> (whereas now we have a duplicated "desired_rate = rate")?

The code in source.c is definitely less confusing than the code in
sink.c. I'd prefer not to have the redundant assignment, but I don't
mind if you leave it there.

-- 
Tanu

https://www.patreon.com/tanuk