From: David Kaye on
Thanks to "John" who emailed me a piece of what I need. I don't blame you for
not wanting to post publicly, given what I've seen so far. I'll send you the
finished project in a couple months when I'm ready to do beta. Thanks again.

From: Nobody on
Try going here first and check ".MP4 versus .M4A file extensions":

http://en.wikipedia.org/wiki/M4A

Then at "See also", follow the link to "Container format", then go to the
subsection "Multimedia container formats". It seems to be a standardized
file format, so you will find the specs there or in one of the links.