[FFmpeg-user] How do I concat MP4 without losing audio sync?

Peter Watkins peter.watkins at biotronik.com
Tue Sep 29 17:35:53 CEST 2015

I've split and joined MP4 files with QuickTime Player Pro 7 before. I'd 
like to learn how to do the same in FFMPEG. I think I have the syntax 
down, but the audio loses sync in the output MP4. I'm taking a video 
called one_through_ten-timestamped.mp4 splitting it into pieces and 
joining it together again into one_through_ten_edited.mp4. The source 
video was created by FFMPEG using x264.

The problem is that the output video loses audio sync after the join point 
(if played in QuickTime Player X. If played in VLC, the audio and video 
drops out at the join point).

I call FFMPEG on the command-line like this:

ffmpeg -f concat -i ~/Desktop/one_through_ten_edit_list.txt -c copy 

When I run this, I get quite a few errors that look like the following:

[mp4 @ 0x7fdd63863000] Non-monotonous DTS in output stream 0:1; previous: 
219766, current: 168772; changing to 219767. This may result in incorrect 
timestamps in the output file.
[concat @ 0x7fdd6300b000] DTS 35840 < 53504 out of order
[mp4 @ 0x7fdd63863000] Non-monotonous DTS in output stream 0:0; previous: 
76544, current: 58880; changing to 76545. This may result in incorrect 
timestamps in the output file.

The edit list is as follows:

file one_through_ten-timestamped.mp4
inpoint 00:00:01.500
outpoint 00:00:05.000
file one_through_ten-timestamped.mp4
inpoint 00:00:09.500
outpoint 00:00:13.000

I understand that I need to split on keyframes--is the problem I'm seeing 
a consequence of splitting on an arbitrary timestamp? If so--how do I 
specify that I only want to split on a keyframe (or determine the 
timestamps for those keyframes)?

OS X 10.9.5
ffmpeg 2.8 (via MacPorts)

I'd rather not attempt to re-compile the latest GIT snapshot on my Mac if 
I can avoid it. That's why I like MacPorts--I don't have to spend 3 weeks 
determining which patches I need to apply to get something to compile and 
run on my Mac. But if I need to, I'll start working on it.

You may notice this is a cross-post from SuperUser--I didn't get any 
responses there. I probably should have sent an email here first--sorry 
about that.

I've put STDOUT/STDERR on my Google Drive (shared) since it's long. I also 
put the original MP4 and the resulting MP4 there.






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