On 01 Jun 2015, at 18:21, t <[email protected]> wrote: > > I know this might not be possible, but I'd at least appreciate understanding > what's going on. > > I have a video with forced keyframes every 2 seconds. Ideally, I was hoping > I'd be able to get frame-perfect slices without having to re-encode. For > example: > > ffmpeg -ss 00:00:00 -i original.mp4 -t 2 -c copy slices_0.mp4 > ffmpeg -ss 00:00:02 -i original.mp4 -t 2 -c copy slices_1.mp4 > ffmpeg -ss 00:00:04 -i original.mp4 -t 2 -c copy slices_2.mp4 > … Are you only interested in the video part ? It might help to disable audio, because audio or video has a delay between them. Another thing you could try is to choose the frame# you want. If the source is 25fps, select video frame 100. That equals 4 sec. If the source is 29.97 things become difficult to be exactly at second points. The same occurs with 23.97 material. You’ll get rounding errors. > > This doesn't quite seem to work. > > Digging more into it, it looks like the first slice is frame-accurate, but > everything after that has a slight offset (it might have other problems, but > I'm just focusing on this for now). The first frame appears ok: > > # same output > ffmpeg -ss 00:00:03 -i original.mp4 -vframes 1 o.png && md5 o.png > ffmpeg -ss 00:00:00 -i slices_1.mp4 -vframes 1 1.png && md5 1.png > > But everything after that, is off: > > # not the same output > ffmpeg -ss 00:00:04 -i original.mp4 -vframes 1 o.png && md5 o.png > ffmpeg -ss 00:00:01 -i slices_1.mp4 -vframes 1 1.png && md5 1.png > > Whatever I do, I get the same result. If I look at the PTS for the original > for frame 60, I get 2.002000 (instead of 2). But, even if I use this for my > slice, I get the same offset. > > What's going on? > > (Probably not realted, but I'm also curious why the first frame of > 0_slices.mp4 has an offset PST/DST, even though the original doesn't) > > > _______________________________________________ > ffmpeg-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/ffmpeg-user
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