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I have a long video with different scenes in it. I want to extract and concatenate 2 scenes from the video (that do not start on an I-frame) using ffmpeg 2.1.4.

For argument, say I want 5 seconds from 01:00 and 02:00.

I can do this:

ffmpeg -ss 01:00 -i in.mkv -ss 02:00 -i in.mkv -filter_complex "
  [0:v]select='lt(t,5)'[v0];
  [0:a]aselect='lt(t,5)'[a0];
  [v0][a0][1:v][1:a]concat=n=2:v=1:a=1
" -c:a libvorbis -t 10 out.mkv

That gives me the movie I want, but select actually forces ffmpeg to decode the entire rest of the movie. So, how do I tell it to truncate the first movie instead of decoding it?

I would prefer to do this with an ffmpeg complex filter, if possible. I know that I can just use -t to recode separate movies first, but the extra encoding step is very slow in my case and also loses a fair amount of quality for this video.

I can't seem to find a filter that truncates the length of a steam. Are there filter nodes that correspond to the -t or -ss parameters?

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1 Answer 1

up vote 3 down vote accepted

concat filter

This method is best if you need to perform additional filtering:

Use the trim, atrim, setpts, asetpts, and concat filters:

ffmpeg -i input -filter_complex \
"[0:v]trim=60:65,setpts=PTS-STARTPTS[v0]; \
 [0:a]atrim=60:65,asetpts=PTS-STARTPTS[a0]; \
 [0:v]trim=120:125,setpts=PTS-STARTPTS[v1];
 [0:a]atrim=120:125,asetpts=PTS-STARTPTS[a1]; \
 [v0][a0][v1][a1]concat=n=2:v=1:a=1[out]" \
-map "[out]" output.mkv
  • setpts and asetpts will prevent a jerky output due to presentation timestamp issues.

  • Make sure to use a recent version. See the FFmpeg Download page for links to builds for Windows, OS X, and Linux.


concat demuxer

Another method is to to create the segments individually and stream copy them instead of re-encoding (to save time and quality), and join them with the concat demuxer.

$ ffmpeg -ss 60 -i input -t 5 -codec copy clip1.mkv
$ ffmpeg -ss 120 -i input -t 5 -codec copy clip2.mkv
$ echo "file 'clip1.mkv'" > concat.txt
$ echo "file 'clip2.mkv'" >> concat.txt
$ ffmpeg -f concat -i concat.txt -codec copy output.mkv
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1  
Ah, thanks. trim is what I was missing. However, it takes a very long time to get to the time offset I specify, as if decoding everything up to it. Also, part of the output was missing audio. To fix, I specified the same input multiple times with -ss, then use trim to truncate the video. You don't need setpts in that case, since ss sets pts to 0. That seemed to work and didn't have weird random pauses during encoding. As for copying streams, I tried that before. It starts at the previous I-frame, so you get a different part of the movie than the one you wanted. –  scubed Mar 18 at 4:05

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