[FFmpeg-trac] #7939(undetermined:new): The concat demuxer changes a constant frame rate into variable one
FFmpeg
trac at avcodec.org
Tue Jun 4 13:55:33 EEST 2019
#7939: The concat demuxer changes a constant frame rate into variable one
-------------------------------------+-------------------------------------
Reporter: RigacciOrg | Type: defect
Status: new | Priority: normal
Component: | Version:
undetermined | unspecified
Keywords: concat | Blocked By:
h264_mp4toannexb codec_time_base |
avg_frame_rate |
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
The file "clip_mpeg2.ts" is an MPEG-2 transport stream in constant frame
rate (as reported by ''ffprobe -show_format -show_streams''):
{{{
codec_time_base=1001/60000
r_frame_rate=30000/1001
avg_frame_rate=30000/1001
}}}
If I concatenate it twice, to produce an '''mp4''' file, I get a variable
frame rate file! The concat command is:
{{{
ffmpeg -f concat -safe 0 -i clip-list.txt -c copy clip-concat.mp4
}}}
where the clip-list.txt contains just two lines with ''file
'clip_mpeg2.ts'''
In the resulting file, the '''codec_time_base''' is changed,
'''r_frame_rate''' and '''avg_frame_rate''' are not exact:
{{{
codec_time_base=607/36000
r_frame_rate=179/6
avg_frame_rate=18000/607
}}}
I suspect that the source file has some bits which triggers this bug,
because I was used to concatenate clips, but I never encountered this
problem.
May be it is related to ticket #5380, because the input file is produced
using '''-bsf:v h264_mp4toannexb'''.
If instead I use an '''mkv''' container as destination, the problem does
not exist.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/7939>
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