[M4IF Technotes] macroblock in B-VOP with co-located block SKIPed

[Christoph Lampert]

Hi,
from what I read and saw in the reference implementation, a macroblock in 
a B-VOP whose co-located block is skipped is _always_ encoded as 
FORWARD mode with motion vector (0,0). 
I also see that no   modb, mb_type, cbp or dbquant  information are saved
because the decoder known about the co-located block already. 
So in fact the B-VOP block is SKIPed, too, because it's a just a copy of
the previous macroblock. 
My question is: What if that's wrong? What if the block is not supposed to
be skiped in the B-VOP, e.g. because there is something like a fast 
moving object which enters the block just for this particular moment. 
It could be something like     background -> object -> background 
with GOP "PBP" where the second background is the same as the first, 
so the co-located block is indeed skiped, but the object somehow has to be
encoded, too.
To me the method looked like a _must_ Isn't there a way to _do_ encode a
motion vector, or at least cbp and residue? 
Christoph Lampert 
P.S. Sorry if this mail was sent more than once. I had trouble with the
mail program, of course... 
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