Over at doom9s:
http://forum.doom9.org/showthread.php?s=&threadid=23100
There are a lot of issues with mp4 encoding and muxing. Apparently one of the problems is that a lot of products don�t follow the standards as they should and only works with software designed for the OS/product. I would guess the p800 is one of them and that why we have such big problems getting it to work with anything AAC or with out the mpegable 1pass.