I recently transferred my media library from iTunes to MediaMonkey. MediaMonkey supports mp4 files, but I am not able to play mp4 files on it, though it can be played on iTunes. I know this is a codec problem, but I want to know exactly what is going on. If a file is an mp4 file and an application claims to support it, why doesn't it work? How do I go about solving this--is installing a codec pack the only way? I've heard bad things about codec packs, some claim that it hurts more than it helps.

I decided to install the codec pack and the file is playable, but not without lags/delays (it would take 2-5 seconds for me to view different parts of the video, whereas on iTunes and with other videos that seem to be natively supported by MediaMonkey , it is instantaneous as it should be. How can solve this? Will I need to sacrifice video quality in order to do this?