The concat demuxer changes a constant frame rate into variable one

[RigacciOrg]

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.

[RigacciOrg]

MPEG-2 transport stream causing frame rate problem with concat demuxer

[Carl Eugen Hoyos]

Please provide the command line you tested together with the complete, uncut console output to make this a valid ticket.

[RigacciOrg]

The -report produced by ffmpeg execution

[Derek Prestegard]

Yeah, this does definitely happen for me too. I end up re-muxing the concatenated output with mp4box. This produces a clean CFR output.

I'm actually currently trying to find a solution for ProRes in MOV. I have the same problem with that, and mp4box doesn't like it :(

[Derek Prestegard]

example of concatenating 3 ProRes MOV files

[Derek Prestegard]

In case anyone is struggling, I found a workaround with the shiny new version of mp4box which understands prores!

First, demux to an elementary prores stream like this

mp4box -raw 1 input.mov

(you'll get a file with an apch extension etc

Then, remux to your target frame rate like this (23.976 in my case):

mp4box -add demuxed.apch:fps=24000/1001 remux.mov