[FFmpeg-devel] [PATCH] Allow 'concat' filter to support inputs with different frame rates

Calvin Walton calvin.walton at kepstin.ca
Wed Mar 8 21:14:25 EET 2017

On Wed, 2017-03-08 at 19:27 +0100, Nicolas George wrote:
> L'octidi 18 ventôse, an CCXXV, Calvin Walton a écrit :
> > 
> > If a later input is higher framerate, this results in dropped frames; if
> > a later input is lower framerate it might cause judder.
> > 
> > The simplest fix is to just set the out links to have '1/0' as the frame
> > rate, the value meaning "unknown/vfr". Note that this changes the 
> I do not think that setting it to 1/0 is the correct fix for this issue.
> Unless I am mistaken, the frame rate is available on all inputs when the
> corresponding code is called: I think the correct fix would be to check
> if all inputs have the same.

Hmm. Setting it to the same as the input value if all inputs match
shouldn't be too hard, I think.

In the actual case of inputs with different frame rates, would it be
better to use the '1/0' value, or should it attempt to calculate a
common framerate that's a multiple of all inputs? (e.g. for 24fps and
30fps inputs, it could pick 120fps).

There's already a TODO listed in the filter code about determining a
common timebase rather than using AV_TIME_BASE - if I'm doing the work
to find a common framerate, I could probably do this at the same time.


Calvin Walton <calvin.walton at kepstin.ca>

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