[FFmpeg-user] concat loses 2 frames or freezes up video

S Andreason sandreas41 at gmail.com
Sun Dec 7 23:15:37 CET 2014


I'd like to report a problem with concat in ffmpeg.
When a mini camera like the 808 or Mobius is configured to loop-record 
and save short files, the need to re-assemble them together is the basis 
for this issue. The 3 minute setting has an overlap of one second, (the 
length of each file is 3:01) so just concattenating them is not enough, 
one second needs to be cut out. Or if I trim or clip out the interesting 
seconds, like say the last 20 seconds of one file and the first 10 
seconds from the following file, than this problem shows up.

Now in the past I used avidemux to append clips. But upon noticing the 
new abilities of ffmpeg to concat files, I hoped this would be more 
fool-proof, scriptable, and faster... It will be when the bugs are fixed 
of course.

Test #1. When I concat trimmed clips made with ffmpeg-0.5, it loses or 
drops 2 frames from the first file. Playback has a jump over the lost 
frames, and a frame by frame count reveals 28 frames in the second as 
indicated by the time position as reported by mplayer on screen 
(pressing [o]) instead of the 30 before and after.

Test #2. When I concat a trimmed clip with one not trimmed, still having 
the encoding and metadata from the camera, then at the joint the video 
freezes up, and pressing the right arrow (in mplayer) to advance the 
time position, reveals it thinks the video is very long now.

Test #3. When I trim a clip with newest ffmpeg, then the concat 
operation output has many errors displayed.
Playback is okay until the joint, when video continues at an accelerated 
rate without any audio, and time position stays stuck. After a while the 
audio resumes in bursts followed by more silence, so it stutters badly.

Test instructions, sample file names and locations, plus debug output, 
are uploaded to:

Waiting for questions? Thank you.


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