[FFmpeg-devel] codec & streams time bases transcode

Michael Niedermayer michaelni at gmx.at
Fri Aug 3 15:29:02 CEST 2012

On Wed, Aug 01, 2012 at 05:27:41PM +0200, Clément Bœsch wrote:
> 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?

The stream copy timebase heuristics have the goal to select a timebase
that allows efficient representation of the input.

While 1576 is about a input file with timebase 2997 or 2997/100 and
you want the output to have a different timebase namely 30000/1001

I would say, its not a failure of the heuristics but rather that you
want them to do something they had not been designed to do at all.
They could be changed to do that of course ...

also theres another question, should 2997/100 always be replaced by
30000/1001 or not ? if not then when should it ? the question matters
for improving the heuristics


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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