Any one know about the differences between the MPEG4-based Codecs?

Hi all
There are many MPEG4-based Codecs such as 3ivx, SEDG, Divx, Xvid and so on. They may not completely conform with MPEG4 standard. Any one know about the differences? It seems that some of the codecs are private and we cannot get the sources and standard format documents.

You might want to ask this very question in the doom9 forums. They’re specialists in these kind of things. Given the amount of reverse engineering they do, they’d know everything about the differences down to the bit.
http://forum.doom9.org

thx