[FFmpeg-devel] MPEG-4 ASP motion vector clamping correct?

Michael Niedermayer michaelni at gmx.at
Fri Dec 16 22:11:58 CET 2011

On Fri, Dec 16, 2011 at 09:45:59PM +0100, Reimar Döffinger wrote:
> Hello,
> I have a question about mpegvideo_common.h
> There is a lot of code like:
> av_clip(src_x, -16, s->width);
> However on the other hand we have the FF_BUG_EDGE flag that changes
> where we start the border extension.
> Why shouldn't this be using s->h_edge_pos instead to follow that?
> Even more so since I think this is also used for H.263
> for which the spec seems quite clear that the decoder should only
> ever care about the rounded-up width, not the non-mod16 part.

I think you are correct, it should use h/v_edge_pos according to the
h263+ spec. I dont know though if this will fix or break real world
it would only make a difference for h263+UMV with %16!=0 and 4mv and
only if the further outside area is sufficiently different and the
encoder actually used such motion vectors.
this could be why it hasnt been noticed before

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The worst form of inequality is to try to make unequal things equal.
-- Aristotle
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