[FFmpeg-devel] [PATCH 4/4] Make the crop filter accept parametric expressions.

[Michael Niedermayer]

On Fri, Sep 10, 2010 at 11:35:54AM +0200, Michael Niedermayer wrote:
> On Fri, Sep 10, 2010 at 09:50:14AM +0200, Stefano Sabatini wrote:
[...]
> >
> >      av_log(link->dst, AV_LOG_INFO, "x:%d y:%d w:%d h:%d\n",
> >             crop->x, crop->y, crop->w, crop->h);
> > @@ -110,6 +175,11 @@ static int config_input(AVFilterLink *link)
> >      }
> >  
> >      return 0;
> > +
> > +fail_expr:
> > +    av_log(NULL, AV_LOG_ERROR,
> > +           "Error when evaluating the expression '%s'\n", expr);
> > +    return ret;
> >  }
> >  
> >  static int config_output(AVFilterLink *link)
> 
> > @@ -131,6 +201,22 @@ static void start_frame(AVFilterLink *link, AVFilterBufferRef *picref)
> >      picref->video->w = crop->w;
> >      picref->video->h = crop->h;
> >  
> > +    crop->var_values[PTS] = picref->pts;
> > +    crop->var_values[POS] = picref->pos;
> > +    crop->x = crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
> > +    crop->y = crop->var_values[Y] = av_eval_expr(crop->y_pexpr, crop->var_values, NULL);
> 
> you must evaluate X after Y again so Y is available to X
> also i think the values should be cliped into sane integer range and maybe a
> NAN check is needed to

and you must set X/Y to NAN before the 3 evaluations
that should catch some invalid expressions refering to themselfs

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras
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