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I'm trying to use ffmpeg to cut video files at precise times. The ffmpeg help shows an option -timecode_frame_start to specify the starting frame but I am unable to get this command to work. The resulting video always starts at the beginning of the original video. Here's an example of the command I'm running:

ffmpeg -i input.mpg -acodec copy -vcodec copy -timecode_frame_start 200 -vframes 210 -n ouput.mpg

I've moved the timecode_frame_start option before and after the other options with no change in results. Is there an additional option I need to specify? I've tried various file formats, mkv, avi, mp4, and it doesn't appear the problem is codec related. Here is one file I've tried:

Am I missing something?

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appears this was answered on the mailing list (and NB that with -vcodec copy you can't "really" get frame specific cutting, since it can only resynchronize on i-frames – rogerdpack Aug 9 '12 at 11:46
@user39364 I asked on the mailing list and it turns out that this option doesn't do what the OP wants. I also learned something new :) – slhck Aug 9 '12 at 11:46

1 Answer 1

up vote 20 down vote accepted

I just learned that the timecode_frame_start does not work like this. The only way to start at specific frames is to convert a number of frames to syntax, or So, if your video is at 25 fps, and you want to start at 133 frames, you would need

133 / 25 = 5.32

So, run

ffmpeg -ss 5.32 -i input.mp4 -c:v libx264 -c:a libfaac out.mp4

Note that cutting on exact frames with bitstream copy (-c:v copy) is not possible since not all frames are intra-coded and can stand on their own.

If you are using a recent version of ffmpeg (> 2.1), transcoding (that is, using anything but -c:v copy), -ss will always be frame-accurate.

You also have the choice to use video filters but audio support might not be exact. And apparently, seeking on frames is still not a feature. You can follow this FFmpeg-users mailing list thread for more info:

you may use -vf select for accurate frame selection (something like -vf 'select=gte(n\,100)' to skip the 100 first frames)

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