[FFmpeg-devel] [PATCH] lavf: inspect more frames for fps when container time base is coarse

[Anssi Hannula]

As per issue2629, most 23.976fps matroska H.264 files are incorrectly
detected as 24fps, as the matroska timestamps usually have only
millisecond precision.

Fix that by doubling the amount of timestamps inspected for frame rate
for streams that have coarse time base. This also fixes 29.970 detection
in matroska.

---

A preferable solution to issue2629 would be to somehow use header values
either from the H.264 stream or from the Matroska stream.

However, AFAICS the framerate inspecting has to be fixed as well anyway
(with e.g. this patch), for cases when we have no reliable header values.

Comments welcome.
---
 libavformat/utils.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/libavformat/utils.c b/libavformat/utils.c
index 1f0164f..0e73e52 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -2273,12 +2273,20 @@ int av_find_stream_info(AVFormatContext *ic)
 
         /* check if one codec still needs to be handled */
         for(i=0;i<ic->nb_streams;i++) {
+            int fps_analyze_framecount = 20;
+
             st = ic->streams[i];
             if (!has_codec_parameters(st->codec))
                 break;
+            /* if the timebase is coarse (like the usual millisecond precision
+               of mkv), we need to analyze more frames to reliably arrive at
+               the correct fps */
+            if (av_q2d(st->time_base) > 0.0005)
+                fps_analyze_framecount *= 2;
             /* variable fps and no guess at the real fps */
             if(   tb_unreliable(st->codec) && !(st->r_frame_rate.num && st->avg_frame_rate.num)
-               && st->info->duration_count<20 && st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
+               && st->info->duration_count < fps_analyze_framecount
+               && st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
                 break;
             if(st->parser && st->parser->parser->split && !st->codec->extradata)
                 break;
-- 
1.7.3