[FFmpeg-devel] [PATCH] ffmpeg: drop format specific stream copy heuristics

Michael Niedermayer michael at niedermayer.cc
Tue Sep 6 18:23:10 EEST 2016

On Tue, Sep 06, 2016 at 11:32:24AM -0300, James Almer wrote:
> On 9/6/2016 9:57 AM, Clément Bœsch wrote:
> >> We don't have time_base in codecpar, so why do we need ticks per frame in it?
> >> > 
> >> > Which time_base does it modify the interpretation of? The field should
> >> > be bundled with that, then.
> > When do we have a mismatch of st->time_base and that "codec time base"?
> st->time_base can be anything. Matroska for example is always 1/1000,
> and mpegps 1/90000.

> "Codec time_base" seems to be codec frame_rate * ticks_per_frame, so
> usually the same as frame_rate, except for codecs like h264 and mpeg2
> where it's twice that.

this only works when codecs use the frame or field rate as basis for
their timebase

With some codecs that is syntactically not even possible
MPEG4 (ISO/IEC 14496-2) stores its timebase as 1/N not M/N for vfr
with for example 30000/1001 that would be different (1/30000) than the
frame rate (30000/1001) (which may be variable)

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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