player: add display sync mode

If this mode is enabled, the player tries to strictly synchronize video
to display refresh. It will adjust playback speed to match the display,
so if you play 23.976 fps video on a 24 Hz screen, playback speed is
increased by approximately 1/1000. Audio wll be resampled to keep up
with playback.

This is different from the default sync mode, which will sync video to
audio, with the consequence that video might skip or repeat a frame once
in a while to make video keep up with audio.

This is still unpolished. There are some major problems as well; in
particular, mkv VFR files won't work well. The reason is that Matroska
is terrible and rounds timestamps to milliseconds. This makes it rather
hard to guess the framerate of a section of video that is playing. We
could probably fix this by just accepting jittery timestamps (instead
of explicitly disabling the sync code in this case), but I'm not ready
to accept such a solution yet.

Another issue is that we are extremely reliant on OS video and audio
APIs working in an expected manner, which of course is not too often
the case. Consequently, the new sync mode is a bit fragile.

1 files changed, 22 insertions, 0 deletions

diff --git a/player/core.h b/player/core.h
index 092775f40e..6ac146624e 100644
--- a/player/core.h
+++ b/player/core.h
@@ -79,6 +79,22 @@ enum seek_precision {
 // Comes from the assumption that some formats round timestamps to ms.
 #define FRAME_DURATION_TOLERANCE 0.0011
 
+enum video_sync {
+    VS_DEFAULT = 0,
+    VS_DISP_RESAMPLE,
+    VS_DISP_RESAMPLE_VDROP,
+    VS_DISP_RESAMPLE_NONE,
+    VS_DISP_VDROP,
+    VS_DISP_NONE,
+    VS_NONE,
+};
+
+#define VS_IS_DISP(x) ((x) == VS_DISP_RESAMPLE ||       \
+                       (x) == VS_DISP_RESAMPLE_VDROP || \
+                       (x) == VS_DISP_RESAMPLE_NONE ||  \
+                       (x) == VS_DISP_VDROP ||          \
+                       (x) == VS_DISP_NONE)
+
 struct track {
     enum stream_type type;
 
@@ -244,7 +260,13 @@ typedef struct MPContext {
     // Redundant values set from opts->playback_speed and speed_factor_*.
     // update_playback_speed() updates them from the other fields.
     double audio_speed, video_speed;
+    bool display_sync_active;
     bool broken_fps_header;
+    double display_sync_frameduration;
+    int display_sync_drift_dir;
+    // Timing error (in seconds) due to rounding on vsync boundaries
+    double display_sync_error;
+    int display_sync_disable_counter;
     /* Set if audio should be timed to start with video frame after seeking,
      * not set when e.g. playing cover art */
     bool sync_audio_to_video;