[XviD-devel] direct mode predictor error

[peter ross]

>Oops, you're right, sorry Pete. I forgot there is another check
>with scaled MV and delta=(0,0) in the beginning, before get_range is
>called. This would have to be changed, of course, but it's not big deal
>since sysKin's ME will because default any minute anyway.

excellent.

> > also whilst browsing the REALmagic source codes, i noticed this:
> >
> > // The hardware decoder is compliant to MPEG-4 definition,
> > // which only allows direct mode when co-located MB is not coded as 
>INTRA
>
>Since the standard allowed referencing I-frames as backward and even GOPs
>like IBI, I find this rather hard to believe. I'd rather consider it a bug
>in REALmagic hardware until somebody shows me where this stands in the
>standard.
>

the following extract from iso14496-2 contradicts the REALmagic
comment.

"7.6.9.5.1 Formation of motion vectors for the direct mode
The direct mode utilises the motion vectors (MVs) of the co-located
macroblock in the most recently I-, P-, or S(GMC)- VOP."

> > it sounds like another silly mpeg-4 limitations, like the every
> > 132 frame i-frame rule & edged blocks must not be field-dct coded.
>
>There also is no 132 frame i-frame rule. There is a "132 frame INTRA-block
>rule". Every macroblock must not be INTER encoded for more than 131 blocks
>in a row. Then it has to be INTRA coded. But if the INTRA block is in
>INTER or INTRA frame doesn't matter. At least that's how I read the
>standard:

okay, okay, a minor typo.

-- pete

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