[Mp4-tech] Query on calculation of global motion vectors

[Subhadeep Chatterjee]

Hi,
I am new in this field and is working on implementing S(GMC) Vops for
MPEG4 decoder. I have a few doubts about the GMC decoding.
In section 7.8.7.3 of MPEG 4 specification ISO/IEC 14496-2 it is written
that macroblocks with mcsel = =  1 don't have their own block motion
vectors, they have pelwise motion vectors for sprite warping obtained
from global motion parameters. But in section 7.8.6 in the description
of the method for sample reconstruction Y and C values are calculated
directly . My question is how to calculate the global motion vectors for
every pixel of the macroblocks with mcsel = = 1 and how exactly the
global motion compensation is done using these motion vectors?
Thanking you in advance
Subhadeep Chatterjee