[M4IF Technotes] GMC

[Kasturi Rangam]

I am trying to under GMC in MPEG4.
Looks like you can have 0, 1, 2 or 3 sprite_warping_points.
To decode a 0 and 1 sprite_warping_points macroblock, you can
fetch the whole macroblock data from the reference to do pixel
prediction.
However, for 2 and 3 warping_points, the motion vector for each
pixel can be anywhere in the reference frame. Thus we might need
to perform 64 data fetches to predict one macroblock.
Is there a range that can be calculated for each macroblock, so that
we can fetch data only once?
Thanks,
Kasturi