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

[Arun Raghavan]

On Sat, 28 Jan 2017, at 10:17 PM, Tanu Kaskinen wrote:
> On Sat, 2017-01-28 at 13:26 +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, though which means that the 96/24 case will
> > require that the default format 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.
> 
> That last paragraph isn't entirely coherent. Feel free to copy-paste
> this:
> 
> Audiophiles who demand "no modification of audio", please note:
> avoiding sample rate coversion doesn't necessarily mean that we don't
> have to do any conversion. We don't reconfigure the sink/source sample
> format dynamically based on the stream format, so if there are
> mismatches between the device and stream sample formats (e.g. 16-bit
> vs. 24-bit), then the samples have to be converted.

I'll fix up the commit message based on this and Peter's comments.

> > @@ -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) {
> > +        /* 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;
> 
> This doesn't work. desired_rate is already set to rate, so this does
> nothing.

The assignment is redundant, but I'd rather leave the assignment for
clarity.

What it _does_ do is avoid the calculation that chooses a desired rate
that is either the default or alternate sample rates.

Regards,
Arun