[Ffmpeg-devel] wrong framerate in mpeg4 file?

Rich Felker dalias
Sat Sep 24 15:38:06 CEST 2005

On Sat, Sep 24, 2005 at 12:03:55PM +0100, M?ns Rullg?rd wrote:
> The Wanderer <inverseparadox at comcast.net> writes:
> > M?ns Rullg?rd wrote:
> >
> >> Rich Felker <dalias at aerifal.cx> writes:
> >>
> >>> Treating 1 specially is definitely wrong. 1/25 is a typical valid
> >>> timebase. The problem is that the codec's framerate is being used
> >>> at all. If the container contains a framerate/timebase, this must
> >>> be used.
> >> Why?  When the two disagree, the container is just as often the one
> >> that's wrong.
> >
> > I have no technical knowledge in this area (which, of course, means I
> > probably shouldn't speak up - but then I'm me), but my guess would be:
> > because it's much easier to change the information (and thus fix the
> > problem) in the container than it is to do the same thing in the codec
> > (without damaging anything, i.e. without transcoding). If the two both
> > have values for the framerate/timebaes, and the player uses the
> > container's value, and it's wrong, then the problem can easily be fixed
> > by remuxing; on the other hand, if the player uses the codec's value and
> > *that* is wrong, there's probably not much you can do about it (in most
> > cases, anyway) without transcoding the video and thus losing quality.
> That's a valid point.  Although the frame rate information on the
> codec level could be corrected without reencoding the video, I've yet
> to see a program capable of doing it.  However, the quality of
> encoders tends to be better than that of muxers, so any random muxer
> is more likely to produce incorrect files than a random encoder.

FYI: when encoding with mencoder and not -vf harddup, the timestamps
in the video stream can be entirely wrong, and the framerate is also
wrong since it's not cfr. The timebase in the avi header is correct.


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