[FFmpeg-devel] [PATCH] libavcodec/zmbvenc.c: don't allow motion estimation out of range.

Tomas Härdin tjoppen at acc.umu.se
Thu Dec 6 21:47:17 EET 2018

ons 2018-12-05 klockan 21:21 +0000 skrev matthew.w.fearnley at gmail.com:
> > From: Matthew Fearnley <matthew.w.fearnley at gmail.com>
> The maximum allowable range for ZMBV motion estimation is [-64..63], since
> the dx,dy values are each stored in the upper 7 bits of a signed char.
> (Previously, the range was capped in the code to 127, resulting in an
> effective range of [-127..126])
> Also fix a range error in the zmbv_me() for-loops ('<' instead of '<='),
> which made the limit asymmetrical [-N..N-1], and also prevented it from
> reaching the blocks touching the bottom/right edges.
> The range is now more symmetrical [-N..N], although this requires separate
> range caps of 64 and 63 for negative and positive dx,dy.
> Practically, this patch fixes graphical glitches e.g. when reencoding the
> Commander Keen sample video with me_range 65 or higher:
>     ffmpeg -i keen4e_000.avi -c:v zmbv -me_range 65 keen4e_me65.avi

I'd expect this problem to pop up with -me_range 64 too, no?

I went over the patch, and it looks fine. But what's up with the xored
logic? It seems like it would compute xored always from the bottom-
right-most MV. The loop in zmbv_me() should probably have a temporary
xored and only output to *xored in if(tv < bv)..


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