EOSHD reports that Canon is working on a new codec for the 5D Mark III based on the MPEG format:
"It will feature a 4-2-2 colour space and a variable bit rate, up to 50mbit. The move is necessary to avoid paying AVCHD / H.264 licensing fees to Panasonic and Sony.
The codec will basically be a slightly improved version of the XF codec, first developed for the XF300 and XF305 professional camcorders which are based on MPEG-2."