[FFmpeg-devel] [PATCH 2/3] avfilter/avfilter: Add AVFILTER_FLAG_SUPPORT_COMMANDS

[Andreas Rheinhardt]

Nicolas George:
> Andreas Rheinhardt (12021-10-09):
>> Currently an API user has no easy way that always works to know
>> whether an AVFilter supports commands. One can check for whether
>> the filter has any AVOption with AV_OPT_FLAG_RUNTIME_PARAM set,
>> but this is a bit of extra work and more importantly it doesn't
>> work for all filters: anequalizer, ladspa, drawtext, overlay, pp,
>> concat and (a)movie accept commands, but have no AVOptions of this
>> type. Tellingly ffprobe/cmdutils.c has to abuse the API and check
>> for AVFilter.process_command to know whether a filter accepts commands.
>>
>> This commit fixes this by adding a new AVFilter flag.
> 
> I do not like it: it requires redundant changes in all the filters.
> 
> It would be more elegant to add avfilter_can_process_commands() that can
> check for the process_command callback.
> 
> Regards,
> 

Quite a lot of these process_command callbacks are actually quite
boilerplate; lots of them are just ff_filter_process_command(). I
actually intended to factor out this common part in a subsequent patch:
https://github.com/mkver/FFmpeg/commits/process_command This would make
the flag non-redundant, because then quite a lot of filters supporting
commands would no longer have a process_command callback at all.

And adding a getter for something that is essentially a flag is IMO very
inelegant.

- Andreas