by Steven Hacker

600 divided by the number of minutes.
Then subtract 1.6 if you are using PCM audio or .2 if you are using AC3 audio.

For example- if your video is 75 minutes:

600/75-1.6= 6.4 or 6400 kbits/sec (PCM audio)

600/75-.2= 7.8 or 7800 kbits/sec (AC3 audio)

These equations work fine for me and leave enough room for menus.