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

[Anton Khirnov <anton@khirnov.net>]

Quoting Paul B Mahol (2023-06-14 19:11:35)
> On Wed, Jun 14, 2023 at 7:01 PM Anton Khirnov <anton@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@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 -

And what useful functionality is provided by this that you cannot
achieve otherwise?

-- 
Anton Khirnov
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