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

[Arun Raghavan]

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. .

> "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).

> 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")?

-- Arun