On Tue, Oct 09, 2012 at 04:38:16PM -0400, Mashiat Sarker Shakkhar wrote:
> This is required due to the way VC-1 handles chroma pull-back which may end
> up causing negative chroma MV for zero luma MV. Edge emulation needs to be
> invoked in such cases.
>
> This problem only affects chroma Y motion vector.
Ahem, that sentence induces cognitive dissonance:
first you see "chroma Y" and think "why not Cb luma",
then you move further and see it's actually "Y motion vector".
As far as I remember, Y is merely one component of motion vector,
so please reformulate it a bit, like "only affects vertical component of
chroma motion vector" or so.
> ---
> libavcodec/vc1dec.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/vc1dec.c b/libavcodec/vc1dec.c
> index 42eb4a5..2683c86 100644
> --- a/libavcodec/vc1dec.c
> +++ b/libavcodec/vc1dec.c
> @@ -430,7 +430,7 @@ static void vc1_mc_1mv(VC1Context *v, int dir)
> if (v->rangeredfrm || (v->mv_mode == MV_PMODE_INTENSITY_COMP)
> || s->h_edge_pos < 22 || v_edge_pos < 22
> || (unsigned)(src_x - s->mspel) > s->h_edge_pos - (mx&3) - 16 -
> s->mspel * 3
> - || (unsigned)(src_y - s->mspel) > v_edge_pos - (my&3) - 16 -
> s->mspel * 3) {
> + || (unsigned)(src_y - 1) > v_edge_pos - (my&3) - 16 - 3) {
> uint8_t *uvbuf = s->edge_emu_buffer + 19 * s->linesize;
>
> srcY -= s->mspel * (1 + s->linesize);
> --
The patch looks OK.
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