lavf: inspect more frames for fps when container time base is coarse

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.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 78431098f9e306ebe27e7698d0ae539e3df2afe9)

Tested with mplayer based on this report
http://thread.gmane.org/gmane.comp.video.mplayer.user/66043/focus=66063

Signed-off-by: Reinhard Tartler <siretart@tauware.de>

2 files changed, 216 insertions, 208 deletions

diff --git a/libavformat/utils.c b/libavformat/utils.c
index 6d6c8308ca..79e70f943e 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -2217,12 +2217,20 @@ 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;
diff --git a/tests/ref/fate/cscd b/tests/ref/fate/cscd
index 75a7725c18..8b89e80a10 100644
--- a/tests/ref/fate/cscd
+++ b/tests/ref/fate/cscd
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