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

[Clément Bœsch]

On Sat, May 26, 2012 at 08:31:12PM -0400, David Rice wrote:
> 
> On May 26, 2012, at 3:17 PM, Clément Bœsch wrote:
> 
> > 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))
> 
> Here's a link to the scene detection filter I've been using, http://www.silicontrip.net/~mark/view.php/lavtools/20111103-yuvdiff. In additions to sequential frame comparison, it can look at sequential fields to detect scene changes that are produced with pulldown.

If you think it can provides better result than the current
implementation, feel free to point out some results :)

-- 
Clément B.
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