mpeg1 and 2 seeking bug

[coder@…]

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 and contain
garbled images.

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.

[coder@…]

Modification to ffplay that causes the bug to appear

[coder@…]

The patch modifies ffplay to seek using the video stream. For xvids, this works
perfectly, for mpeg2s, it produces garbled images and the error messages in the
bug report.

I've got a small (200k, 160x120, 10 seconds) test movie if you need one.

[coder@…]

mpeg2 file that causes the bug to appear.

[coder@…]

File created using
FFMPEG_PARAMS=-i testmovies/tmp/tmp.wav -t 10.04 -i \

testmovies/tmp/160x120_frame%07d.png -y -r 25 -b 9000 \
-vcodec mpeg2video mpeg2_160x120_25_10_audio.mpg

ffmpeg -pass 1 ${FFMPEG_PARAMS}
ffmpeg -pass 2 ${FFMPEG_PARAMS}

[mans@…]

MPEG PS doesn't indicate keyframes.