player: fix audio drift computation at different playback speeds

This computed nonsense if the user set a playback speed other than 1
(in addition to the display-sync speed change).

1 files changed, 9 insertions, 8 deletions

diff --git a/player/video.c b/player/video.c
index f6ab3d44c9..043abeb3b1 100644
--- a/player/video.c
+++ b/player/video.c
@@ -854,11 +854,11 @@ 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)
+// Compute the relative audio speed difference by taking A/V dsync into account.
+static double compute_audio_drift(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
+    // Least-squares linear regression, using relative real time for x, and
+    // audio desync 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)
@@ -870,7 +870,7 @@ static double compute_audio_speed(struct MPContext *mpctx, double vsync)
         struct frame_info *frame = &mpctx->past_frames[n + 1];
         if (frame->num_vsyncs < 0)
             return NAN;
-        double y = frame->av_diff + x;
+        double y = frame->av_diff;
         sum_x += x;
         sum_y += y;
         sum_xy += x * y;
@@ -923,10 +923,11 @@ static void adjust_audio_resample_speed(struct MPContext *mpctx, double vsync)
         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);
+            double drift = compute_audio_drift(mpctx, vsync);
             if (isnormal(drift)) {
-                drift /= mpctx->audio_speed; // eliminate intended speed
-                audio_factor = 1.0 / drift / mpctx->speed_factor_v;
+                // other = will be multiplied with audio_factor for final speed
+                double other = mpctx->opts->playback_speed * mpctx->speed_factor_v;
+                audio_factor = (mpctx->audio_speed - drift) / other;
                 MP_VERBOSE(mpctx, "Compensation factor: %f\n", audio_factor);
             }
         }