[FFmpeg-devel] [PATCH v3] lavfi: add new iteration API

[Josh Allmann]

On Tue, 14 Apr 2020 at 01:53, Josh de Kock <josh at itanimul.li> wrote:
>
> Hi,
>
> On Mon, Apr 13, 2020, at 10:32 PM, Josh Allmann wrote:
> > Hi,
> >
> > On Sat, 24 Mar 2018 at 14:40, Josh de Kock <josh at itanimul.li> wrote:
> > >
> > > Signed-off-by: Josh de Kock <josh at itanimul.li>
> > > ---
> > >  configure                |  29 +-
> > >  doc/APIchanges           |   4 +
> > >  doc/writing_filters.txt  |   6 +-
> > >  libavfilter/allfilters.c | 823 +++++++++++++++++++++++++----------------------
> > >  libavfilter/avfilter.c   |  50 +--
> > >  libavfilter/avfilter.h   |  29 +-
> > >  libavfilter/version.h    |   3 +
> > >  7 files changed, 489 insertions(+), 455 deletions(-)
> > >
> >
> > This is a couple years too late, but wanted to drop a note that this
> > particular API change was breaking : it made avfilter_register a
> > no-op. The consequence is that it's much more difficult to maintain
> > filters out-of-tree; preserving the old behavior without changes to
> > user code requires a special build of ffmpeg that has the filter
> > configured/compiled in. The recommended workaround of using
> > avfilter_graph_alloc_filter requires more effort to wire the filter in
> > explicitly. It also doesn't allow for conveniences such as using
> > avfilter_graph_parse, since there doesn't seem to be a way to make
> > filters accessible via avfilter_get_by_name outside of ffmpeg compile
> > time.
> >
> > If there is another workaround that I'm missing, please let me know,
> > or if there's some deeper rationale for the decision to disable this
> > feature.
>
> This was actually an intentional change, there was some trouble with how
> external codecs/filters/etc should be handled.
>
> Since this was an unsupported use-case which was quite sensitive to ABI the
> change was there to explicitly prevent people (ab)using the API like this.  It
> was also to prepare for potentially a new API to implement this in a proper
> fashion (but as you can see this was never completed).
>
> I did begin working on this again a little while back but due to an unfortunate
> data-loss I will have to start from scratch to continue working on it (yes, yes
> 'where's your backup?' I know). It's likely to be something I will be working
> on in the future since I will be doing FFmpeg stuff again soon.
>
> There is also the discussion of 'do we want this?' from a more ideological
> perspective which we will have to re-discuss, maybe something like gstreamer is
> more suited for the majority of the use-cases (?).
>

Thanks for the explanation Josh. For what it's worth, count me as
being at least one API user for which out-of-tree filter capability
would be very helpful. (And to preempt some other reactions, "use
gstreamer" is not really helpful for us either...)

Josh