Canon EOS 5D Mark II firmware v2.0.3 makes the camera better suited for filmmaking courtesy of several tweaks to the video and audio capabilities of the camera. The 30 frames per second video rate has been replaced by a 29.97 frames per second rate at all resolutions, and there is also a new high-def 23.976 frames per second rate, both matching TV production standards. The audio sampling frequency has been increased from 44.1KHz to 48KHz, and a 64-step manual audio level control has been added, answering a very common request from videographers.
There is also now a histogram display when shooting movies manually, to assist with correct exposure, as well as both shutter and aperture-priority movie shooting modes that let the videographer control only one or other variable. Canon has also noted that there are improvements in camera / lens communication when manual sensor cleaning is used.
One important point to note is that while the new firmware is capable of playing back movies recorded with older firmware, the reverse is not true. Movies recorded on a 5D Mark II with firmware 2.0.3 will not be playable on bodies running the older firmware, and will instead yield an error message.
The new firmware is available immediately for download free of charge. A document from Canon USA explains the changes in more detail.