[FFmpeg-devel] [PATCH 12/21] fftools/ffmpeg_filter: reject filtergraphs with zero outputs

[Paul B Mahol]

On Wed, Jun 14, 2023 at 7:01 PM Anton Khirnov <anton at khirnov.net> wrote:

> Quoting Paul B Mahol (2023-06-14 18:53:52)
> > On Wed, Jun 14, 2023 at 6:51 PM Anton Khirnov <anton at khirnov.net> wrote:
> >
> > > Nothing useful can be done with them currently.
> > > ---
> > >  fftools/ffmpeg_filter.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
> > > index 4f7565e44e..54c7ed1f5c 100644
> > > --- a/fftools/ffmpeg_filter.c
> > > +++ b/fftools/ffmpeg_filter.c
> > > @@ -845,6 +845,12 @@ FilterGraph *fg_create(char *graph_desc)
> > >          ofilter->name      = describe_filter_link(fg, cur, 0);
> > >      }
> > >
> > > +    if (!fg->nb_outputs) {
> > > +        av_log(fg, AV_LOG_FATAL, "A filtergraph has zero outputs,
> this is
> > > not supported\n");
> > > +        ret = AVERROR(ENOSYS);
> > > +        goto fail;
> > > +    }
> > > +
> > >  fail:
> > >      avfilter_inout_free(&inputs);
> > >      avfilter_inout_free(&outputs);
> > > --
> > > 2.40.1
> > >
> > >
> >
> > NAK
> >
> > This is functionality breaking change.
> >
>
> Exactly what useful functionality is broken by this?
>
> > And why something that is currently supported should be not supported any
> > more.
>
> It is not really supported. The scheduling logic is based around output
> streams and cannot work without them.
>

This works currently:

ffmpeg -i tom.wav -lavfi astats,anullsink -f null -


> --
> Anton Khirnov
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