Originally posted by Telomar
On the subject of AAC in iTunes I believe you would find decoding it is supported through QT6. Not positive on that one but I have a hunch that's why you can play things in the AAC format.
Don't expect an encoder in iTunes too soon though as it costs money to add. If you want that get a QT6 Pro Key. Don't re-encode mp3s to mp4s though. As has already been pointed out there is no point. You already have the inherent loss from compressing it to mp3 and then you will lose more quality going to mp4. If you have the originals then encode them to mp4 otherwise you are stuck with mp3s.
Yes, Quicktime6 Pro will do all your encoding. Also yes, the reason that iTunes can play AAC is that it is iTunes is integrated with Quicktime.