[FFmpeg-devel] [PATCH] [2/??] [3/3] Filter graphs - Parser for a graph description

[Michael Niedermayer]

On Wed, Mar 19, 2008 at 08:24:41PM +0100, Vitor Sessak wrote:
> Michael Niedermayer wrote:
> > On Wed, Mar 19, 2008 at 07:48:04PM +0100, Vitor Sessak wrote:
> >> Hi Michael, Vmrsss
> >>
> >> Michael Niedermayer wrote:
> >>> On Wed, Mar 19, 2008 at 03:01:41PM +0000, vmrsss wrote:
> >>>> Hi Michael,
> >>>>
> >>>> On 19 Mar 2008, at 14:00, Michael Niedermayer wrote:
> >>> [...]
> >>>>> [...]
> >>>>>> As for the extra operator, you are right. However, I claim that in
> >>>>>> order to allow reusable libraries of graphs in your syntax you will
> >>>>>> have to provide a renaming operator, eg:
> >>>>>>
> >>>>>>  	{tmp1/in} (in)overlay(out) {tmp2/out}  = (tmp1) overlay (tmp2)
> >>>>> You are inventing some syntax and then complain about it, there is  
> >>>>> nothing
> >>>>> in the code nor in any mails from vitor suggesting anything like  
> >>>>> above.
> >>>> Hmm, I might not have made myself clear: sure you haven't suggested  
> >>>> anything like the above, I am arguing (and made a specific example in  
> >>>> support) that you **have** to if you want to reuse filters.
> >>> Look, as there is nothing specified about "reuseable libraries" any
> >>> system/syntax could be used, this clearly would allow to use "your syntax"
> >>> as well thus this is a proper proof that it cannot be worse than "your
> >>> syntax".
> >> One problem about libraries of filter chains is that ideally they should 
> >> be more flexible than just some graph hunk. Citing an example of what 
> >> I'd like to be possible:
> >>
> >> AVFilter avfilter_vf_rotate =
> >> {
> >>      .name = "rotate";
> >>      .init = init;
> >>
> >>      {some magic to make it a pseudofilter}
> >> }
> >>
> >> static void init(char *args, AVFilter *ctx) {
> >>      int ang= atoi(args);
> >>      switch (ang) {
> >>      case 90:
> >>          ctx->actual_filter = "transpose,vflip";
> >>          break;
> >>      case 180:
> >>          ctx->actual_filter = "hflip,vflip";
> >>          break;
> >>      case 270:
> >>          ctx->actual_filter = "vflip,transpose";
> >>          break;
> >>      else
> >>          snprintf(ctx->actual_filter, "rotate_slow=%d", ang);
> >>          break;
> >>      }
> >> }
> >>
> >> But for doing this it would have to be a real filter, not something that 
> >> pasted some code while parsing the chain.
> > 
> > no, implement 1 filter doing generic rotations/flip/transpose with special
> > cases for what can be done faster.
> > And then just replace "transpose" / "vflip" / "hflip" by the appropriate
> > generic filter string
> > 
> > no code duplication, simple and fast
> 
> Well, it's only simpler if you consider the pseudo-filter framework as 
> part of the complexity of the rotate filter. It's usually simpler to 
> read/maintain pieces code that do just one operation.
> 
> Also, I cited that more as an example. One could think in more cases 
> like using movie_src, set_pts and overlay to make a add_logo filter, 
> etc. Anyway, if this complexity is ever added, the pseudo-filter code 
> now in avfiltergraph.c would be only used for those pseudo-filters, and 
> not always as is in current code.

If you really want to insert filters, the logic way would be

av_insert_filter() which directly works on libavfilter/avfilter.h
structs, i dont see the need for a second layer API

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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