[FFmpeg-soc] libavfilter: fps ignored in ffmpeg command line

[Víctor Paesa]

Hi,

On Dec 31, 2007 9:04 AM, Vitor Sessak <vitor1001 at gmail.com> wrote:
> Hi
>
> Víctor Paesa wrote:
> > Hi,
> >
> > The filter fps seems ignored in the ffmpeg command line.
> > This is the scenario:
>
> [...]
>
> > Input #0, avi, from 'input.avi':
> >   Duration: 00:00:20.2, start: 0.000000, bitrate: 30349 kb/s
> >     Stream #0.0: Video: dvvideo, yuv420p, 720x576 [PAR 0:1 DAR 0:1], 25.00 tb(r)
> >     Stream #0.1: Audio: pcm_s16le, 48000 Hz, stereo, 1536 kb/s
> > Output #0, avi, to 'output.avi':
> >     Stream #0.0: Video: mpeg4, yuv420p, 720x576 [PAR 0:1 DAR 0:1],
> > q=2-31, 200 kb/s, 25.00 tb(c)
> >     Stream #0.1: Audio: mp2, 48000 Hz, stereo, 64 kb/s
>
> [...]
>
> > The input and output AVI have the same 25 fps.
>
> I'm not really sure if the filter is supposed to change this. The filter
> infrastructure is designed to get pictures+timestamps as input and give
> pictures+timestamps as output. I'd say setting the output framerate is
> beyond filtering. For example,
>
> ffmpeg -i input.avi -vfilters fps=1 -r 25 -y output.avi
>
> should give a 25 fps output but with a different frame every 1 second.
> But indeed I get a crash with your command line and vf_fps.c do not
> seems to handle a rate greater than the input rate. I'll have a look
> into it...

I feel the libavfilter framework should support frame rate change as that
is listed as part of the wishes/ideas for libavfilter in:
http://wiki.multimedia.cx/index.php?title=FFmpeg_Summer_Of_Code_2007

Of course, updating the stated scope, documenting the intention
of vf_fps.c, or adding an entry to the TODO list are also valid ways of
fixing the issue ;-)

Regards,
Víctor