[FFmpeg-devel] [PATCH] Add scale filter

[Stefano Sabatini]

On date Tuesday 2009-10-27 13:34:06 +0100, Michael Niedermayer encoded:
> On Tue, Oct 27, 2009 at 02:59:38AM +0100, Stefano Sabatini wrote:
[...]
> > +static void start_frame(AVFilterLink *link, AVFilterPicRef *picref)
> > +{
> > +    ScaleContext *scale = link->dst->priv;
> > +    AVFilterLink *out = link->dst->outputs[0];
> > +    int64_t gcd;
> > +
> > +    out->outpic = avfilter_get_video_buffer(out, AV_PERM_WRITE, out->w, out->h);
> > +    out->outpic->pts = picref->pts;
> > +
> 
> > +    out->outpic->pixel_aspect.num = picref->pixel_aspect.num * out->h * link->w;
> > +    out->outpic->pixel_aspect.den = picref->pixel_aspect.den * out->w * link->h;
> > +
> > +    gcd = av_gcd(out->outpic->pixel_aspect.num, out->outpic->pixel_aspect.den);
> > +    if (gcd > 1) {
> > +        out->outpic->pixel_aspect.num /= gcd;
> > +        out->outpic->pixel_aspect.den /= gcd;
> > +    }
> 
> this can overflow and it should use av_reduce()

Changed to:

    out->outpic->pts = picref->pts;

    av_reduce(&out->outpic->pixel_aspect.num, &out->outpic->pixel_aspect.den,
              (int64_t)picref->pixel_aspect.num * out->h * link->w,
              (int64_t)picref->pixel_aspect.den * out->w * link->h,
              INT_MAX);

But there is still the possibility to get an overflow in
the expressions:
(int64_t)picref->pixel_aspect.num * out->h * link->w
(int64_t)picref->pixel_aspect.den * out->w * link->h, 

I could check for example for:
(int64_t)out->h * link->w < MAX_INT
(int64_t)out->w * link->h < MAX_INT

in config_props() and then eventually fail, but maybe you can suggest
some more clever way to check it.

> > +
> > +    scale->slice_dir = 0;
> > +    avfilter_start_frame(out, avfilter_ref_pic(out->outpic, ~0));
> > +}
> > +
> > +static void draw_slice(AVFilterLink *link, int y, int h)
> > +{
> > +    ScaleContext *scale = link->dst->priv;
> > +    int out_h;
> > +    AVFilterPicRef *cur_pic = link->cur_pic;
> > +    uint8_t *data[4];
> > +
> 
> > +    if (!scale->slice_dir && y != 0 && y + h != link->h) {
> > +        av_log(scale, AV_LOG_ERROR, "Slices start in the middle!\n");
> > +        return;
> > +    }
> > +    if (!scale->slice_dir) {
> 
> this check can be factored out

Done.
  
> > +        scale->slice_dir = y ? -1 : 1;
> > +        scale->slice_y   = y ? link->dst->outputs[0]->h : y;
> > +    }
> > +
> > +    data[0] = cur_pic->data[0] + y * cur_pic->linesize[0];
> > +    data[3] = cur_pic->data[3] + y * cur_pic->linesize[3];
> > +
> > +    if (link->format == PIX_FMT_PAL8) {
> 
> > +        data[1] = cur_pic->data[1];
> > +        data[2] = cur_pic->data[2];
> 
> can be factored out

Fixed.

Regards.
-- 
FFmpeg = Free & Frenzy Mystic Problematic Elitist Geek
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