[FFmpeg-devel] codec & streams time bases transcode

[Clément Bœsch]

Hi,

I'm working on ticket¹ about an issue while transmuxing a MOV. The
original file contains a timecode, which is transmitted through metadata
and thus a timecode track is written as well in the output.

Unfortunately, the codec time base received in the MOV muxer is invalid:
2997/1 instead of 1001/30000 (or something like 2997/100), which make the
timecode init fails (can be workarounded with -r 30000/1001 for example).

This happens because of the heuristics around line 3000 in ffmpeg.c where
the codec time base copy is not triggered (it will work if transmuxing to
MXF on the other hand). Reverting 618fb9cc fixes the issue, but will break
some other stuff, so it's not a solution.

All of this time base copies and heuristics look pretty fragile to me (and
are actually broken in this case); anyone has any thoughts about what
could be done here, and this is supposed to be fixed?

I mentioned in the ticket that I would propose a patch to ignore the
timecode if it is badly set, but this would actually hide the real issue
we have here so I'm not sure about that.

[1]: https://ffmpeg.org/trac/ffmpeg/ticket/1576

-- 
Clément B.
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