[FFmpeg-devel] [RFC PATCH] vf_fps: Requantize pts of CFR videos

[Calvin Walton]

On Wed, 2021-12-22 at 23:04 +0100, Michael Niedermayer wrote:
> On Wed, Dec 22, 2021 at 11:20:26AM -0500, Calvin Walton wrote:
> > This is mostly to avoid oddities in small framerate adjustments
> > when you
> > have input videos from containers such as matroska, where the pts
> > values
> > are quantized with a large enough error to cause issues.
> > 
> 
> breaks a 60fps 1/60000 timebase input downconverted with -vf fps=30:-
> 0.01
> the expected result is identical to -vf fps=30 but
> 
> -i 60fps.mov -bitexact -vf fps=30:-0.01  -t 2 -v 99 fps.flv
> the expected output is that either all odd or all even frames are
> returned but
> its a mix after this patch
> I cannot share the input file but this should reproduce with any
> 60fps
> input i hope. If not say so and ill try to find some other file that
> shows this

I'll take a look at this. Hopefully I can reproduce it with an
artificially created file (if so, I'll make a test).

If you could provide the logs from the fps filter at 'verbose' log
level for the initial segment of the file (first ~1 second of so) that
would provide helpful information.

It's possible that the reason you're having a problem with fps=30:-0.01
is that I'm applying the start offset in the wrong position in the
conversion; I'll try moving it around.

-- 
Calvin Walton <calvin.walton at kepstin.ca>