[FFmpeg-devel] [PATCH] lavfi/select/WIP: add scene detection.

[Clément Bœsch]

On Sat, May 26, 2012 at 06:45:09PM +0200, Michael Niedermayer wrote:
[...]
> > +static void set_scene_values(AVFilterContext *ctx, AVFilterBufferRef *picref)
> > +{
> > +    SelectContext *select = ctx->priv;
> > +    AVFilterBufferRef *prev_picref = select->prev_picref;
> > +
> > +    if (prev_picref &&
> > +        picref->video->h == prev_picref->video->h &&
> > +        picref->video->w == prev_picref->video->w) {
> > +        int64_t score = 0, diff;
> > +        int x, y;
> > +
> 
> > +#define ABSSC(a) abs((int)p[a] - (int)q[a])
> > +        for (y = 0; y < picref->video->h; y++) {
> > +            for (x = 0; x < picref->video->w; x++) {
> > +                const uint8_t *p =      picref->data[0] + y *      picref->linesize[0] + x*3;
> > +                const uint8_t *q = prev_picref->data[0] + y * prev_picref->linesize[0] + x*3;
> > +                score += ABSSC(0) + ABSSC(1) + ABSSC(2);
> > +            }
> 
> theres some optimized code in dsputil to calculate sum of abs diff
> not sure how easy it is to use from lavfi but above looks pretty
> inefficient so a TODO/FIXME should be added at least
> 

It seems some DSP stuff is going to move to lavu. I added a "TODO: use
DSPContext.sad[]".

Also, I'm looking for a better algorithm ATM; I'd like to avoid having the
need of a user threshold (there was a linked paper mentioning another
method), so users would just have to use select=scene, with scene being 0
or 1 (and eventually in the whole [0,1] so it could be used like
select=gt(scene\,0.8))

-- 
Clément B.
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