[FFmpeg-devel] [PATCH] lavfi: remove the duplicate expression evaluation.

[wm4]

On Mon, 9 Jan 2017 11:46:01 +0100
Nicolas George <george at nsup.org> wrote:

> Le decadi 20 nivôse, an CCXXV, Jun Zhao a écrit :
> > I didn't find any case about x depends on y or y depends y.  
> 
> Some users have occasionally asked for it, IIRC.
> 
> > If have this dependency relationship , why the code don't handle out_w/out_h in 
> > crop?  
> 
> Ideally, all variables should be able to be expressed based on any
> other, and the system should find an order of evaluation that works.
> Alas, this is rather complex to implement.

A start would be not having to do this in every filter ever.

Other filter systems (such as vapoursynth) do not even make the mistake
of conflating user language and underlying mechanisms.