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sink-input: Implement resampler pseudo rewinding

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This patch uses the two previous patches to implemnt pseudo-rewinding for the
resamplers by feeding some old data into the resampler after a reset. This is
necessary because PA is using external resamplers that do not implement
rewinding.

To get exactly the same output data from the resampler after a rewind if possible,
the matching period is calculated. This is the number of input samples that produces
an integral number of output samples. After the matching period, the resampler state
repeats. If the matching period is not too large, feeding history into the resampler
will start at a point that is a multiple of the matching period back in time. Then
the resampler will produce exactly the same samples.

The PA_RESAMPLER_MAX_HISTORY value has been replaced by PA_RESAMPLER_MAX_DELAY_USEC
and the required number of history samples is calculated from the sink input sample
rate. The number of history samples can be as large as about 12500.

This fixes glitches during volume changes when the sink runs on a rate different
from the sink input rate.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/120>
This commit is contained in:
Georg Chini 2021-01-01 00:23:10 +01:00 • committed by PulseAudio Marge Bot
parent 656179a8fe
commit da539ed336
3 changed files with 159 additions and 19 deletions
Download patch file Download diff file Expand all files Collapse all files

43
src/pulsecore/resampler.c
View file

@ -122,6 +122,24 @@ static int (* const init_table[])(pa_resampler *r) = {
#endif
};
static void calculate_gcd(pa_resampler *r) {
unsigned gcd, n;
pa_assert(r);
gcd = r->i_ss.rate;
n = r->o_ss.rate;
while (n != 0) {
unsigned tmp = gcd;
gcd = n;
n = tmp % n;
}
r->gcd = gcd;
}
static pa_resample_method_t choose_auto_resampler(pa_resample_flags_t flags) {
pa_resample_method_t method;
@ -354,6 +372,7 @@ pa_resampler* pa_resampler_new(
/* Fill sample specs */
r->i_ss = *a;
r->o_ss = *b;
calculate_gcd(r);
if (am)
r->i_cm = *am;
@ -485,6 +504,7 @@ void pa_resampler_set_input_rate(pa_resampler *r, uint32_t rate) {
r->out_frames = 0;
r->i_ss.rate = rate;
calculate_gcd(r);
r->impl.update_rates(r);
}
@ -502,6 +522,7 @@ void pa_resampler_set_output_rate(pa_resampler *r, uint32_t rate) {
r->out_frames = 0;
r->o_ss.rate = rate;
calculate_gcd(r);
r->impl.update_rates(r);
@ -1634,6 +1655,28 @@ pa_usec_t pa_resampler_get_delay_usec(pa_resampler *r) {
return (pa_usec_t) (pa_resampler_get_delay(r, false) * PA_USEC_PER_SEC / r->i_ss.rate);
}
/* Get GCD of input and output rate. */
unsigned pa_resampler_get_gcd(pa_resampler *r) {
pa_assert(r);
return r->gcd;
}
/* Get maximum resampler history. The resamplers have finite impulse response, so really old
* data (more than 2x the resampler latency) cannot affect the output. This means, that in an
* ideal case, we should re-run 2 - 3 times the resampler delay through the resampler when it
* is rewound. On the other hand this would mean for high sample rates that more than 25000
* samples would need to be used (384k * 33ms). Therefore limit the history to 1.5 times the
* maximum resampler delay, which should be fully sufficient in most cases and allows to run
* at least more than one delay through the resampler in case of high rates. */
size_t pa_resampler_get_max_history(pa_resampler *r) {
if (!r)
return 0;
return (uint64_t) PA_RESAMPLER_MAX_DELAY_USEC * r->i_ss.rate * 3 / PA_USEC_PER_SEC / 2;
}
/*** copy (noop) implementation ***/
static int copy_init(pa_resampler *r) {