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I am currently using ffmpeg to split videos into 10 seconds segments. I have taken two approaches but neither seems to yield the desired results. Approach number one is using basic cutting with the -t and -ss options to get the segments. This gives close to accurate segments but it has some issues with the frames in the ending of some videos. The second option is using segment: great and fast but it gives segments of not equal duration. Any idea how to get segments of the same duration and no issues in the frames? In other words if I play them in a list it should play smoothly

General way

ffmpeg – i input.mp4  -ss <start> -t <duration> -vcodec copy -acodec copy output%03d.mp4

Using segment

ffmpeg -i input.mp4 -c copy -map 0 -segment_time 8 -f segment output%03d.mp4
  • Did you find any solution or reason? – Dr.jacky Aug 23 '15 at 11:42
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The issue with the frames are very likely the results of using h264 and not re-encoding the video. h264 usually doesn't have single frames (unless encoded with an intra profile) but groups of frames (GOPs), ffmpeg will cut at a keyframe position ie. at the end or beginning of a GOP. Or not in the case of your first approach, giving you issues with the affected GOPs.

The issue should be resolved by re-encoding (-vcodec libx264 -preset slow) or if that also yields errors transcode to a lossless codec like jpeg2000 (-vcodec libopenjpeg) cut your video and then encode into h264 again (or any other codec you may prefer).

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  • What about using -g parameter?! (set GOP size) – Dr.jacky Aug 23 '15 at 11:37
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    That wouldn't help you with frame accurate cutting. The issue is that there are GOPs. if you split a video within a GOP you will destroy frames at the end of your clip. – PTS Aug 23 '15 at 19:35
  • What do you mean by "you will destroy frames at the end of your clip" ?! – Dr.jacky Aug 24 '15 at 3:20
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    Frames inside a GOP need all the other frames in the GOP, so if you cut a GOP the frames that are left don't have all the needed information. Technically you could re-encode just the last GOP but I don't think there is a tool that would do this for you. – PTS Aug 24 '15 at 19:33
  • See: en.wikipedia.org/wiki/Group_of_pictures – PTS Aug 24 '15 at 19:35

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