RepoMirrors
/
mpv
mirror of https://github.com/mpv-player/mpv
1
0
Fork 0
Code Issues Releases Wiki Activity

player: try to compensate actual audio drift 

We always let audio slowly desync until a threshold is reached, and then
pushed it back by applying a maximum compensation speed. Refine what
comes afterwards: instead of playing with the nominal video speed, use
the actual required audio speed for keeping sync as measured by the A/V
difference. (The "actual" speed is the ideal speed with A/V differences
added.)

Although this works in theory, it's somewhat questionable how much this
works in practice. The ideal time value is actually not exact, but is
the time at which the frame is scheduled (could be compensated by using
the time_left calculations in handle_display_sync_frame()). It doesn't
account for speed changes or catastrophic discontinuities. It uses only
10 past frames.
This commit is contained in:
wm4 2015-11-13 22:51:39 +01:00
parent c362c3d7ae
commit 70d46a9fb8
2 changed files with 41 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
player/core.h
View File

@ -99,6 +99,7 @@ struct frame_info {
double pts;
double duration; // PTS difference to next frame
double approx_duration; // possibly fixed/smoothed out duration
double av_diff; // A/V diff at time of scheduling
int num_vsyncs; // scheduled vsyncs, if using display-sync
};

40
player/video.c
View File

@ -854,6 +854,32 @@ static bool using_spdif_passthrough(struct MPContext *mpctx)
return false;
}
// Compute the relative audio speed by taking A/V dsync into account.
static double compute_audio_speed(struct MPContext *mpctx, double vsync)
{
// Least-squares linear regression, using relative file PTS values for x,
// and audio time for y. Assume speed didn't change for the frames we're
// looking at for simplicity. This also should actually use the realtime
// (minus paused time) for x, but use vsync scheduling points instead.
if (mpctx->num_past_frames <= 10)
return NAN;
int num = mpctx->num_past_frames - 1;
double sum_x = 0, sum_y = 0, sum_xy = 0, sum_xx = 0;
double x = 0;
for (int n = 0; n < num; n++) {
struct frame_info *frame = &mpctx->past_frames[n + 1];
if (frame->num_vsyncs < 0)
return NAN;
double y = frame->av_diff + x;
sum_x += x;
sum_y += y;
sum_xy += x * y;
sum_xx += x * x;
x -= frame->num_vsyncs * vsync;
}
return (sum_x * sum_y - num * sum_xy) / (sum_x * sum_x - num * sum_xx);
}
static void adjust_audio_resample_speed(struct MPContext *mpctx, double vsync)
{
struct MPOpts *opts = mpctx->opts;
@ -893,6 +919,19 @@ static void adjust_audio_resample_speed(struct MPContext *mpctx, double vsync)
double max_correct = opts->sync_max_audio_change / 100;
double audio_factor = 1 + max_correct * -mpctx->display_sync_drift_dir;
if (new == 0) {
// If we're resetting, actually try to be clever and pick a speed
// which compensates the general drift we're getting.
double drift = compute_audio_speed(mpctx, vsync);
if (isnormal(drift)) {
drift /= mpctx->audio_speed; // eliminate intended speed
audio_factor = 1.0 / drift / mpctx->speed_factor_v;
MP_VERBOSE(mpctx, "Compensation factor: %f\n", audio_factor);
}
}
audio_factor = MPCLAMP(audio_factor, 1 - max_correct, 1 + max_correct);
mpctx->speed_factor_a = audio_factor * mpctx->speed_factor_v;
}
}
@ -1002,6 +1041,7 @@ static void handle_display_sync_frame(struct MPContext *mpctx,
update_av_diff(mpctx, time_left * opts->playback_speed);
mpctx->past_frames[0].num_vsyncs = num_vsyncs;
mpctx->past_frames[0].av_diff = mpctx->last_av_difference;
if (resample) {
adjust_audio_resample_speed(mpctx, vsync);