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

[Arun Raghavan]

On Sun, 29 Jan 2017, at 10:23 AM, Arun Raghavan wrote:
> 
> 
> 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.

However, I am going to send in a modification. I think we need to
fallback to the old logic if the condition within that if is not met.

-- Arun