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

[Michael Niedermayer]

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
samples.
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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