[Ffmpeg-devel] MPEG2 seeking broken

Ulrich von Zadow coder
Thu Jul 27 16:12:50 CEST 2006

Ivan Kalvachev wrote:
> As Ulrich mail indicates this could have something in common with
> Motion Vectors so I'll assume that the problem is in the
> forward/backward_f_code been set to 0.
> If that's the case then setting error_resilence lower than
> FF_ER_COMPLAINT (2) would make the crash go away.

There is no crash in my case - I simply get the wrong frame displayed. 
This happens even if the movie contains only I-frames. The error occurs 
with current svn and the version from March 2, 2006.

> Another possibility is that pict_type is IPB and the only know other
> type is DC intra picture that is available only in mpeg1.
> So are these crashes with mpeg1 streams?

The movies are all synthetic, 26 frames long and generated by ffmpeg. 
The seek is simply from a frame in the middle of the movie to frame 4. 
In the case of mpeg1 and mpeg2, the last movie frame is shown. The error 
shows up with or without muxed audio in the stream.

> Anyway, all these possibilities are supposed to show themselves in
> normal decoding not only when seeking.

With our synthetic movies, there are no errors when we don't seek.

> So my last question is Are you parsing the stream headers (sequence
> start, extensions, display, etc.) before starting decoding right after
> seeking to I-Frame?

Not sure what you mean by this, so I assume not. How is this supposed to 
be done?

Note that we've got this issue consistently reproducible here, it's just 
that it happens in the context of a large application. If anyone would 
like to send me a diff or some code instrumented with appropriate output 
statements to verify some of the assumptions being made, I'd gladly help.



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