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

[Michael Niedermayer]

On Sun, Sep 12, 2010 at 01:51:23AM +0200, Stefano Sabatini wrote:
> On date Saturday 2010-09-11 19:05:46 +0200, Michael Niedermayer encoded:
> > On Sat, Sep 11, 2010 at 11:35:58AM +0200, Stefano Sabatini wrote:
> > > On date Friday 2010-09-10 23:13:45 +0200, Michael Niedermayer encoded:
> > > > On Fri, Sep 10, 2010 at 06:33:36PM +0200, Stefano Sabatini wrote:
> > > > [...]
> > > > > > also i think the values should be cliped into sane integer range and maybe a
> > > > > > NAN check is needed to
> > > > > 
> > > > > The clipping is already performed, and NAN check added.
> > > > 
> > > > no its not, you dont clip the double before converting to int
> > > > and if iam not mistaken C doesnt gurantee not representable types for that
> > > > not just crashing your program
> > > 
> > > Check attached and tell me if you like it.
> > [...]
> > > +# trembling effect
> > > +crop='10+10*sin(n/10):20+20*sin(n/5):w-2*x:h-2*y
> > > +
> > > +# erratic camera effect depending on timestamp
> > > +crop='20+20*sin(3*t):10+10*sin(2*t):w-2*x:h-2*y'
> > > +
> > > +# set x depending on the value of y
> > > +crop='y:10+10*sin(n/10):w-2*x:h-2*y'
> > > + at end example
> > 
> > if x and y change per frame but w/h cannot then this looks odd
> 
> If you prefer we can use x0/y0 in place of x/y for the w and h
> expressions.

for filters like above this makes as much sense as x/y
what you mean (but dont conciously realize) is the maximum x/y that the
x/y expressions can generate for any input.
sadly we dont know these and its not easy to calculate for a computer


>  
> > [...]
> > >  static int config_input(AVFilterLink *link)
> > >  {
> > >      AVFilterContext *ctx = link->dst;
> > >      CropContext *crop = ctx->priv;
> > >      const AVPixFmtDescriptor *pix_desc = &av_pix_fmt_descriptors[link->format];
> > > +    int ret;
> > > +    const char *expr;
> > > +    double res;
> > > +
> > > +    crop->var_values[E  ]   = M_E;
> > > +    crop->var_values[PHI]   = M_PHI;
> > > +    crop->var_values[PI ]   = M_PI;
> > > +    crop->var_values[X  ]   = NAN;
> > > +    crop->var_values[Y  ]   = NAN;
> > > +    crop->var_values[W  ]   = ctx->inputs[0]->w;
> > > +    crop->var_values[H  ]   = ctx->inputs[0]->h;
> > > +    crop->var_values[N  ]   = 0;
> > >  
> > >      av_image_fill_max_pixsteps(crop->max_step, NULL, pix_desc);
> > >      crop->hsub = av_pix_fmt_descriptors[link->format].log2_chroma_w;
> > >      crop->vsub = av_pix_fmt_descriptors[link->format].log2_chroma_h;
> > >  
> > > -    if (crop->w == 0)
> > > -        crop->w = link->w - crop->x;
> > > -    if (crop->h == 0)
> > > -        crop->h = link->h - crop->y;
> > > +    if ((ret = av_parse_expr(&crop->x_pexpr, crop->x_expr, var_names,
> > > +                             NULL, NULL, NULL, NULL, 0, ctx)) < 0 ||
> > > +        (ret = av_parse_expr(&crop->y_pexpr, crop->y_expr, var_names,
> > > +                             NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> > > +        return AVERROR(EINVAL);
> > > +
> > > +    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
> > > +    crop->var_values[Y] = av_eval_expr(crop->y_pexpr, crop->var_values, NULL);
> > > +    /* evaluate again x as it may depend on y */
> > > +    crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
> > >  
> > > +    if (normalize_double(&crop->x, crop->var_values[X]) < 0 ||
> > > +        normalize_double(&crop->y, crop->var_values[Y]) < 0) {
> > > +        av_log(ctx, AV_LOG_ERROR,
> > > +               "Too big value or invalid expression for x or y. "
> > > +               "Maybe the expression for x:'%s' or for y:'%s' is self-referencing.\n",
> > > +               crop->x_expr, crop->y_expr);
> > > +        return AVERROR(EINVAL);
> > 
> > this could trigger for unknown pos/ts
> 
> ???

NAN in (unknown ts/pos), NAN out


> 
> > [...]
> > > +    /* FIXME: when the TB will be settable */
> > > +    crop->var_values[T]   = (double)picref->pts / AV_TIME_BASE;
> > 
> > AV_NOPTS_VALUE
> 
> How do you suggest to deal with that case? One option would be to use
> the last valid values

we could have a filter that fills in missing timestamps by repeating the last
or extrapolating


>  (as I'm already doing with x/y).

i was unaware of that

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

Observe your enemies, for they first find out your faults. -- Antisthenes
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