[Ffmpeg-devel] wrong framerate in mpeg4 file?

Måns Rullgård mru
Sat Sep 24 13:03:55 CEST 2005

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.

M?ns Rullg?rd
mru at inprovide.com

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