[Ffmpeg-devel] MPEG2 seeking broken
Ulrich von Zadow
Wed Jul 26 18:10:18 CEST 2006
Ulrich von Zadow wrote:
> Has this been fixed? We seem to be running into the same issue here, and
> if there's any info we can provide to help, we will.
Ok, some more information on what I have been able to determine here:
Seeking in mpeg1 and mpeg2 streams using
av_seek_frame(formatcontext, vstream, time, AV_SEEK_FLAG_BACKWARD);
causes messages like
[mpeg2video @ 0xb4ba61d0]Warning MVs not available
[mpeg2video @ 0xb4ba61d0]releasing zombie picture
[mpeg2video @ 0xb4ba61d0]warning: first frame is no keyframe
Also, the frames returned are clearly not the ones I seeked to.
The code works with other codecs - I've tested huffyuv, mjpeg, mpeg4,
msmpeg and xvid. If the stream index is set to -1 and the time
calculation changed appropriately:
av_seek_frame (formatcontext, -1, time, AV_SEEK_FLAG_BACKWARD);
then everything works. The first two warning messages still appear, but
the frames shown are the correct ones and the 'no keyframe' message
doesn't appear anymore.
Any comments on this? I notice that fplay uses -1 as stream index when
seeking, so the bug doesn't appear there. What risks am I taking if I
omit the stream index? How does the decoder find the previous keyframe
in this case?
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