From 90d7e51643273a14dfb9a4db622abb7da4e0aa5f Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Thu, 23 Apr 2015 19:35:15 +0200
Subject: demux_mkv: attempt to fix rounded timestamps

There is some potential for breakage. If it happens, this might have to
be disabled by default.
---
 DOCS/man/options.rst | 12 ++++++++++++
 demux/demux_mkv.c    | 19 ++++++++++++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/DOCS/man/options.rst b/DOCS/man/options.rst
index ef914982a7..47f4c15152 100644
--- a/DOCS/man/options.rst
+++ b/DOCS/man/options.rst
@@ -2112,6 +2112,18 @@ Demuxer
     will be slower (especially when playing over http), or that behavior with
     broken files is much worse. So don't use this option.
 
+``--demuxer-mkv-fix-timestamps=<yes|no>``
+    Fix rounded Matroska timestamps (enabled by default). Matroska usually
+    stores timestamps rounded to milliseconds. This means timestamps jitter
+    by some amount around the intended timestamp. mpv can correct the timestamps
+    based on the framerate value stored in the file: if the timestamps does
+    not deviate more than 1 frame (as implied by the framerate), the timestamp
+    is rounded to the next frame, which should undo the rounding the muxer
+    did.
+
+    This can break playback if the framerate value stored in the file is too
+    high.
+
 ``--demuxer-rawaudio-channels=<value>``
     Number of channels (or channel layout) if ``--demuxer=rawaudio`` is used
     (default: stereo).
diff --git a/demux/demux_mkv.c b/demux/demux_mkv.c
index 4ae734cb5b..39b271e1b6 100644
--- a/demux/demux_mkv.c
+++ b/demux/demux_mkv.c
@@ -24,6 +24,7 @@
 #include <stdio.h>
 #include <inttypes.h>
 #include <stdbool.h>
+#include <math.h>
 #include <assert.h>
 
 #include <libavutil/common.h>
@@ -190,6 +191,7 @@ struct demux_mkv_opts {
     int subtitle_preroll;
     double subtitle_preroll_secs;
     int probe_duration;
+    int fix_timestamps;
 };
 
 const struct m_sub_options demux_mkv_conf = {
@@ -198,11 +200,13 @@ const struct m_sub_options demux_mkv_conf = {
         OPT_DOUBLE("subtitle-preroll-secs", subtitle_preroll_secs,
                    M_OPT_MIN, .min = 0),
         OPT_FLAG("probe-video-duration", probe_duration, 0),
+        OPT_FLAG("fix-timestamps", fix_timestamps, 0),
         {0}
     },
     .size = sizeof(struct demux_mkv_opts),
     .defaults = &(const struct demux_mkv_opts){
         .subtitle_preroll_secs = 1.0,
+        .fix_timestamps = 1,
     },
 };
 
@@ -2327,6 +2331,19 @@ exit:
     return res;
 }
 
+static double fix_timestamp(demuxer_t *demuxer, mkv_track_t *track, double ts)
+{
+    mkv_demuxer_t *mkv_d = demuxer->priv;
+    if (demuxer->opts->demux_mkv->fix_timestamps && track->default_duration > 0) {
+        // Assume that timestamps have been rounded to the timecode scale.
+        double quant = mkv_d->tc_scale / 1e9;
+        double rts = rint(ts / track->default_duration) * track->default_duration;
+        if (fabs(rts - ts) < quant)
+            ts = rts;
+    }
+    return ts;
+}
+
 static int handle_block(demuxer_t *demuxer, struct block_info *block_info)
 {
     mkv_demuxer_t *mkv_d = (mkv_demuxer_t *) demuxer->priv;
@@ -2349,7 +2366,7 @@ static int handle_block(demuxer_t *demuxer, struct block_info *block_info)
         return 0;
     }
 
-    current_pts = tc / 1e9 - track->codec_delay;
+    current_pts = fix_timestamp(demuxer, track, tc / 1e9) - track->codec_delay;
 
     if (track->type == MATROSKA_TRACK_AUDIO) {
         if (mkv_d->a_skip_to_keyframe)
-- 
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