On Thu, Aug 2, 2012 at 12:10 PM, Roger Pack <rogerdpa...@gmail.com> wrote:
> > Could you provide a sample that does not seek to a keyframe with > > ffmpeg -ss x -i input out.png > > (I tested this yesterday on random mpeg2video samples and afaict, > > it did work.) > > With me, I get this: > > with this file: http://rogerdpack.t28.net/incoming/sintel.mpg > > $ ffmpeg -i sintel.mpg -vcodec copy -acodec copy -ss 90.0 > starting_at_90.mpg > > then try and use it again: > > $ ffmpeg -i starting_at_90.mpg -vframes 1 -f image2 -an snap.jpg > > I get this warning message: > [mpeg2video @ 01f09860] warning: first frame is no keyframe > > Anybody know if this is expected? I almost don't think it is... I could be wrong on my understanding, so someone please correct me if I am... I believe that does no seeking there. Putting -ss after the input will cause ffmpeg to demux up to the requested timestamp, so it's not quite related to seeking (putting -ss before the input will seek the input file). Since -a/vcoded copy avoids re-encoding, it just copies the packets (without regard to keyframes, iiuc). The packet closest to 90 seconds probably isn't a keyframe, but since that's where you requested the start it ffmpeg starts copying packets from there anyway. Maybe there should be the ability to set a start time and copy packets, starting with the closest keyframe packet to the requested time... --Michael
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