[FFmpeg-devel] [PATCH] mpeg2dec: fix decoding field pictures

Michael Niedermayer michael at niedermayer.cc
Sat Feb 10 00:56:56 EET 2018

On Fri, Feb 09, 2018 at 02:03:24AM +0900, Nekopanda wrote:
> - Fix field selection for skipped macroblocks
> For B field pictures, the spec says,
> > The prediction shall be made from the field of the same parity as the field being predicted.
> I did it.
> - Fix motion vector rounding for chroma components
> In 16x8 motion compensation, for lower 16x8 region, the input to mpeg_motion() for motion_y was "motion_y + 16", which causes wrong rounding. For 4:2:0, chroma scaling for y is dividing by two and rounding toward zero. When motion_y < 0 and motion_y + 16 > 0, the rounding direction of "motion_y" and "motion_y + 16" is different and rounding "motion_y + 16" would be incorrect.
> We should input "motion_y" as is to round correctly. I add "is_16x8" flag to do that.

please split this patch in 2.
I think these are 2 independant bugfixes.

also please update the fate checksums so make fate does not break after
either patch


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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