On Mon, Jul 23, 2012 at 7:12 PM, Carl Eugen Hoyos <[email protected]> wrote:
> Michael Bradshaw <mbradshaw@...> writes: > > > Anyone have any answers on these two things? If the answer to the > > above would be "yes" can anyone else verify that "ffmpeg -dump > > -loglevel debug -ss 38 -i 704x480-m2v-ac3.mpg -vframes 1 out.jpg" does > > not seek to a keyframe? > > As said, afaict it does seek to a keyframe. > (But I may of course be wrong.) > > I am quite sure neither MPEG-PS nor MPEG-TS has the ability to seek to a keyframe. Its been a problem for me for a while and i've been over this code many times. All they do is a binary search for the timestamp, and when they arrive close enough, they are done. To compensate for this, decoders like MPEG-2 will simply discard frames until they see a keyframe to start decoding from, so visual corruption is avoided. If you run those codecs with AVCodeContext.flags2 set to CODEC_FLAG2_SHOW_ALL, you'll probably get plenty of corrupted frames before a real frame is shown, however i do not know how to do that via ffmpeg commandline to demonstrate.
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