[M4IF Technotes] object based coding, profiles and bandwidth limitation

[Xiaodong Cai]

Dear all :
It is well known that mpeg-4 is object-based coding which supports arbitrary shape coding in its core profile. Does anybody can tell me why it is not supported in simple profile?
I believe in many cases, the arbitrary shape object based coding can provide a better compression rate than rectangle shape or frame coding so that it can serve low bandwidth applications (in simple profile). 
So is it possible to use arbitrary shape coding technique (by video segmentation) for simple profile ? Also , are there anyone can tell me if there are bandwidth limitation designed in the standard for different profiles ? if so , why ?
Many thanks . 
sheldon 
University of Sussex 
UK
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