[FFmpeg-devel] [PATCH] libavfilter-soc: implement pad filter

[Stefano Sabatini]

On date Thursday 2009-07-16 01:59:37 +0200, Michael Niedermayer encoded:
> On Thu, Jul 16, 2009 at 12:49:21AM +0200, Stefano Sabatini wrote:
> > On date Wednesday 2009-07-15 01:03:12 +0200, Stefano Sabatini encoded:
> > [...]
> > > I changed the logic of the patches, now the buffer informations are
> > > stored in the link rather than in the params.
> > > 
> > > This allows for simpler API usage, also makes it possible crop/pad
> > > chains which caused troubles before. I'll provide a better explanation
> > > with a further patchset, since these ones need to be cleaned up
> > > /fixed.
> > > 
> > > Since the last version:
> > > * fixed ffmpeg.c
> > > * fixed hflip
> > > 
> > > Yet to come:
> > > * fix vflip
> > > * fix for leaks?
> > > * add a regression test
> > > * direct rendering is not implemented, it would be better to post it
> > >   as a separate patchset since this is hard enough
> > 
> > I added a pix_fmt field to the get_video_buffer, as this information
> > is not known in the links (i.e. when configuring the chain).

That wasn't true, my mind was obfuscated when I conceived that thing.

> > Also added a regression test for the pad.
> > 
> > > I also suspect the exp_w, exp_h, x, y params in the picref are not really
> > > required.
> > 
> > Patches updated.
> 
> would it be possible to split that stuff up a little?
> (self contained changes with explanations of why its done as is done and
>  so on)
> 
> that is assuming you want this reviewed ...

Uhm, no the patches were not still ready for review but I wanted
backup / share my progress in the meaningwhile.

Now I'm posting other patches, what I'd like to discuss are these two
points:

* I tried both to put the information required for padding (x, y, h,
  w, exp_h, exp_w) in the link and pass it in the get_video_buffer()
  params, they're pretty equivalent but the second method (as in the
  patch) seems more flexible, as the information is not stored
  statically in the links, so it doesn't need a reconfiguration when
  changing it.  (BTW maybe we can as well remove w/h from the link,
  that should make simpler to implement variable size filters, I still
  have to experiment with this).

* I tinkered about the vflip problem much time, and I could'nt find some 
  way to keep the previous behavior with the new system.
  The new system assumes that the position of the area to pad
  (referred by the x/y params in the picref) needs to be invariant
  when passing a picref to the next filter.
  That's because the pad filter expects this:

static void start_frame(AVFilterLink *link, AVFilterPicRef *picref)
{
    PadContext *pad = link->dst->priv;
    AVFilterPicRef *ref2 = avfilter_ref_pic(picref, ~0);
    link->dst->outputs[0]->outpic = ref2;

    ref2->data[0] -=  pad->x             + (pad->y * ref2->linesize[0]);
    ref2->data[1] -= (pad->x>>pad->hsub) + (pad->y * ref2->linesize[1]>>pad->vsub);
    ref2->data[2] -= (pad->x>>pad->hsub) + (pad->y * ref2->linesize[2]>>pad->vsub);
    if (ref2->data[3])
        ref2->data[3] -= pad->x + pad->y * ref2->linesize[3];
    ref2->x -= pad->x;
    ref2->y -= pad->y;
    ref2->w = pad->out_w;
    ref2->h = pad->out_h;

    avfilter_start_frame(link->dst->outputs[0], ref2);
}

to work.

My solution is to change the way the vflip filter works, as in the
attached patch, which makes it less efficient (indeed it becomes
necessary to allocate an extra buffer and copy data to it as in the
hflip filter).

Please comment on these.

Regards.
-- 
FFmpeg = Fierce & Faithful Mere Plastic Emblematic Gadget
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