[FFmpeg-devel] [PATCH] avformat/matroskaenc: Increase time stamp precision to AV_TIME_BASE

[michael.dirks at xaymar.com]

From: Michael Fabian 'Xaymar' Dirks <info at xaymar.com>

Increases the time stamp precision to 1 microsecond, the same as
AV_TIME_BASE. This hopefully prevents demuxers from being confused on
the number of frames/samples we actually have per second, and should
mark all future Matroska/WebM content as being constant rate.

Work-around for: 259, 6406, 7927, 8909, 9124.

Signed-off-by: Michael Fabian 'Xaymar' Dirks <info at xaymar.com>
---
 libavformat/matroskaenc.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index ad7b0bf2c6..474e44485a 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -1917,7 +1917,8 @@ static int mkv_write_header(AVFormatContext *s)
         return ret;
     pb = mkv->info_bc;
 
-    put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000);
+    // Set time base to 1 microsecond.
+    put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000000 / AV_TIME_BASE);
     if ((tag = av_dict_get(s->metadata, "title", NULL, 0)))
         put_ebml_string(pb, MATROSKA_ID_TITLE, tag->value);
     if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
@@ -1959,11 +1960,11 @@ static int mkv_write_header(AVFormatContext *s)
         int64_t metadata_duration = get_metadata_duration(s);
 
         if (s->duration > 0) {
-            int64_t scaledDuration = av_rescale(s->duration, 1000, AV_TIME_BASE);
+            int64_t scaledDuration = s->duration;
             put_ebml_float(pb, MATROSKA_ID_DURATION, scaledDuration);
             av_log(s, AV_LOG_DEBUG, "Write early duration from recording time = %" PRIu64 "\n", scaledDuration);
         } else if (metadata_duration > 0) {
-            int64_t scaledDuration = av_rescale(metadata_duration, 1000, AV_TIME_BASE);
+            int64_t scaledDuration = metadata_duration;
             put_ebml_float(pb, MATROSKA_ID_DURATION, scaledDuration);
             av_log(s, AV_LOG_DEBUG, "Write early duration from metadata = %" PRIu64 "\n", scaledDuration);
         } else {
@@ -2038,12 +2039,12 @@ static int mkv_write_header(AVFormatContext *s)
     // after 4k and on a keyframe
     if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
         if (mkv->cluster_time_limit < 0)
-            mkv->cluster_time_limit = 5000;
+            mkv->cluster_time_limit = 5000000;
         if (mkv->cluster_size_limit < 0)
             mkv->cluster_size_limit = 5 * 1024 * 1024;
     } else {
         if (mkv->cluster_time_limit < 0)
-            mkv->cluster_time_limit = 1000;
+            mkv->cluster_time_limit = 1000000;
         if (mkv->cluster_size_limit < 0)
             mkv->cluster_size_limit = 32 * 1024;
     }
@@ -2724,6 +2725,7 @@ static int webm_query_codec(enum AVCodecID codec_id, int std_compliance)
 static int mkv_init(struct AVFormatContext *s)
 {
     int i;
+    MatroskaMuxContext *mkv = s->priv_data;
 
     if (s->nb_streams > MAX_TRACKS) {
         av_log(s, AV_LOG_ERROR,
@@ -2752,10 +2754,13 @@ static int mkv_init(struct AVFormatContext *s)
     }
 
     for (i = 0; i < s->nb_streams; i++) {
-        // ms precision is the de-facto standard timescale for mkv files
-        avpriv_set_pts_info(s->streams[i], 64, 1, 1000);
+        // Use µs precision (same as FFmpeg)
+        avpriv_set_pts_info(s->streams[i], 64, 1, AV_TIME_BASE);
     }
 
+    // Scale the configured cluster_time_limit to microseconds.
+    mkv->cluster_time_limit = av_rescale(mkv->cluster_time_limit, 1000, AV_TIME_BASE);
+
     return 0;
 }
 
-- 
2.31.1.windows.1