[FFmpeg-soc] [soc]: r1773 - in libavfilter: Makefile allfilters.h avfilter.c vf_rot90.c

[Bobby Bingham]

On Sun,  6 Jan 2008 14:19:12 +0100 (CET)
vitor <subversion at mplayerhq.hu> wrote:
> +static void draw_slice(AVFilterLink *link, int y, int h)
> +{
> +    RotContext *rot = link->dst->priv;
> +    AVFilterPicRef *in  = link->cur_pic;
> +    AVFilterPicRef *out = link->dst->outputs[0]->outpic;
> +    int i, j, plane;
> +
> +    /* luma plane */
> +    for(i = y; i < h; i ++)
> +        for(j = 0; j < link->w; j ++)
> +            *(out->data[0] +   j *out->linesize[0] + i) =
> +                *(in->data[0]+ i * in->linesize[0] + j);
> +
> +    /* chroma planes */
> +    for(plane = 1; plane < 3; plane ++) {
> +        for(i = y >> rot->vsub; i < h >> rot->vsub; i++) {
> +            for(j = 0; j < link->w >> rot->hsub; j++)
> +                *(out->data[plane] +   j *out->linesize[plane] + i) =
> +                    *(in->data[plane]+ i * in->linesize[plane] + j);
> +        }
> +    }
> +
> +    avfilter_draw_slice(link->dst->outputs[0], y, h);
> +}

This is a bad use of slices.

Slices must be a rectangle whose width spans the whole image, and whose
height is arbitrary.  By transposing a slice, you end up with a valid
area which spans the height of the image, but not necessarily width.

Even worse, the last line tells the next filter the dimensions of the
input slice, which are not the same as the dimensions of your output,
even assuming your output is valid as a slice.  Run with "-vfilters
slicify,transpose" (after updating to the latest update I made - the
auto-inserted scale filters would mask the problem otherwise), or even
"-vfilters transpose,transpose" to see the result.

There are a few possible solutions:

a) Change the concept of slices to allow arbitrary rectangular
regions.  I had briefly considered this early on, but dismissed it.
Maybe it's worth considering?

b) Add a flags field to input pads, with a flag for "requires entire
image at once" and auto-insert a buffer filter before filters with this
flag.  I've been thinking about doing this anyways, because the next
option (c) is the only one which works currently, and I don't like the
inconsistency it causes in how you have to implement some filters.

c) Make the filter process the frame in either request_frame() or in
end_frame().  This will guarantee that you have the entire frame before
you start processing it, and you therefore have enough input to
guarantee a valid slice for output.  See vf_scale or vf_overlay for
examples.

Also, could you please set the aspect ratio for the output frames
correctly.

I haven't looked at vf_rotate yet, but I guess this probably applies
there as well.
-- 
Bobby Bingham
Never trust atoms.  Or anything made of atoms.
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