MPEG2 hardware question

[Joe Fenton]

I could look this up in the code, but I'm hoping one of the XviD codec programmers could give me a quick nod. I have an MPEG2 hardware decoder which works on several different parts of the bitstream independently. I was wondering if the macroblock decoder could be fed a fake mpeg2 bitstream which made it process mpeg4 macroblocks. The idea is to take hardware meant to speed up mpeg2 decoding and use it to speed up mpeg4 decoding. Could I slap a few symbols in front of the mpeg4 macroblock which made it look like an mpeg2 macroblock bitstream?

Could you possibly point me to the right docs describing the mpeg4 bitstream? That would also be helpful.

Thanks! :)