By default, MediaMonkey relies on Quicktime to play m4a / m4b / AAC files.  

Unfortunately, Quicktime has a bug that prevents playback of very large 

(~500MB) audiofiles, which prevents MediaMonkey from playing such files.



The workaround to this problem is to purchase the MediaMonkey AAC / M4A

encoder addon--it uses an alternate codec that does not have that bug.



See: http://www.mediamonkey.com/addons/input-output/