[FFmpeg-user] FFmpeg concat outputs bad video file

Ryan Mirman rsgm123 at gmail.com
Tue Oct 6 04:24:22 CEST 2015

When I try to concat these 3 video files, it outputs a video with a too 
short of a duration and way too high of a bitrate.

I am not sure if I am using ffmpeg the wrong way, if the audio is 
corrupted, or if it is a bug with ffmpeg?

Here are the files,

These webm files have been recorded from webrtc through firefox on 
The files used in each command are found in the linked mega folder.

This command is enough to demonstrate the problem I am having,
     ffmpeg -f concat -i list.txt -c copy output.webm
this gives an output file that is too short but has a very high bitrate.
(The log for this is concat_copy.log)

VLC may not play these videos at all, but firefox does for the most part 
and I have been using GNOME mplayer.
In this, you should see a video that says it is 1 second long but plays 
some audio after that but the video stops.

Also note that running
     ffmpeg -f concat -i list.txt output.webm
outputs a file with the same duration as before, but a much lower bitrate.
This should be similar to the last output video.
(The log for this is concat_transcode.log)

If you first convert the videos,
     ffmpeg -i 0.webm 0_fixed.webm
(the output for these are 0_fixed.log, ...)
and this above command with the corrected list file,
     ffmpeg -f concat -i list.txt -c copy output.webm
it outputs a file with the correct duration of 3 seconds and a normal 
This should play like a normal video. (sorry for the crackly mic)
(The log for this is concat_fixed_copy.log)

It is possible that the audio was corrupted from recording, but even so 
this behavior is not expected.
This does not happen from chrome on windows.

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