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

[Anton Khirnov]

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.

-- 
Anton Khirnov