[FFmpeg-devel] [PATCH] libavfilter-soc: implement pad filter

[Vitor Sessak]

Stefano Sabatini wrote:
> On date Tuesday 2009-05-05 20:49:55 +0200, Vitor Sessak encoded:
>> Stefano Sabatini wrote:
>>> On date Tuesday 2009-04-28 22:03:53 +0200, Stefano Sabatini encoded:
> [...]
>>> In order to be memcpy-less we need some API redesign, I started to
>>> look at it and I'm thinking about to put in the link other fields (x,
>>> y, w_exp, and h_exp).
>> Why in the link and not as a parameter of request_frame() as suggested  
>> by Michael [1]?
> 
> |What effect would that have on a decoder changing the output image size?
> |Also what about 
> |- int (*request_frame)(AVFilterLink *link);
> |+ int (*request_frame)(AVFilterLink *link, int width, int height, int left, int top);
> |
> |where left/top is extra memory being allocated ...
> 
> Would that also require a corresponding change in avfilter_draw_slice():
> avfilter_draw_slice(AVFilterLink *link, int left, int top);

The way I see it is that the request_frame() call would just assures 
that you have enough memory allocated, but picture->data[] would point 
always to the picture (and thus draw_slice() would not need any 
modification). A padding (with unallocated junk) filter would look like

int request_frame(AVFilterLink *link, int width, int height, int left, 
int top)
{
     avfilter_request_frame(link->src->inputs[0],
                            FFMAX(width, ctx->width),
                            FFMAX(height, ctx->height),
                            FFMAX(left, ctx->padleft),
                            FFMAX(top, ctx->padtop));

     link->src->inputs[0]->picture->data[0] += ctx->padleft;
     link->src->inputs[0]->picture->data[0] += ctx->padtop * stride;

     [... data[1,2,3] following the same idea ...]

     [... avfilter_start_frame() and etc...]
}

-Vitor