[FFmpeg-devel] [PATCH V1 0/2] Use avctx->framerate first for frame rate setting

[mypopy at gmail.com]

On Sat, Apr 27, 2019 at 8:22 PM Gyan <ffmpeg at gyani.pro> wrote:
>
>
>
> On 27-04-2019 05:25 PM, Carl Eugen Hoyos wrote:
> > 2019-04-27 13:17 GMT+02:00, Jun Zhao <mypopydev at gmail.com>:
> >> perfer avctx->framerate first than use avctx->time_base when
> >> setting the frame rate to encoder. 1/time_base is not the
> >> average frame rate if the frame rate is not constant.
> > But why would the average framerate be a good choice to set
> > the encoder timebase?
> >
>
> Also, note that x264/5 RC looks at the framerate.
> See
> https://code.videolan.org/videolan/x264/commit/c583687fab832ba7eaf8626048f05ad1f861a855
>
> I can generate a difference with x264 by setting -enc_time_base to
> different values (with vsync vfr).
> Maybe check that this change does not lead to a significant change in
> output. Although I think this would be still an improvement for those
> cases where r_frame_rate >> avg_frame_rate
>
> Gyan
Yes, framerate and time_base is not close correlation in vfr case,
e,g, I can setting the framerate = 60fps, but time_base = 1/1000 s,
then setting pts like:

time_base = 1/1000 s = 1 millisecond
framerate = 60 fps per second
PTS       0----16----33----50----66----83----100 ...

PTS delta  16    17    17    16    17    17 ...

we will get 16ms * 20 frames + 17 ms * 40 frames = 1000ms