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

[Víctor Paesa]

Hi,

On Dec 31, 2007 12:03 PM, Vitor Sessak <vitor1001 at gmail.com> wrote:
> Hi
>
> Víctor Paesa wrote:
> > Hi,
> >
> > On Dec 31, 2007 9:04 AM, Vitor Sessak <vitor1001 at gmail.com> wrote:
> >> Víctor Paesa wrote:
> >>> Hi,
> >>>
> >>> The filter fps seems ignored in the ffmpeg command line.
>
> [...]
>
> >>> 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
>
> Actually the filter framework does support frame rate change.
> If you do
>
> ffmpeg -i input.avi -vfilters fps=1 output.avi
>
> where input.avi has a rate of 25 fps, you'll have
>
> Input -> 25 fps
> Filtered input -> 1 fps
> Output -> 25 fps
>
> The only problem is that the output rate (set in ffmpeg.c) is equal by
> default to the unfiltered input rate. The filter does its job, but I
> agree it would be more reasonable to set the default output rate to the
> filtered input rate. That would unfortunately have a small problem:
> imagine for example overlaying a 20 fps and a 30 fps movie together. The
> filter output will not have a fixed frame rate, so creating and setting
> a frame_rate field in the AVFilterLink structure will not make a lot of
> sense. A second problem would be to allow broken filters to set
> frame_rate to a value not coherent with the interval between timestamps.

Yeah, I was thinking of patching vf_overlay.c as attached:

> Bobby, Michael, what is your opinion?

Regards,
Víctor
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