Does anyone know?
apple does
http://support.apple.com/kb/HT5016 (http://support.apple.com/kb/HT5016)
EDIT: That's just security updates so it's not very helpful
In the attachment,
7973.m4a was encoded using CoreAudioToolBox shipped with QT7.7.0.
7978.m4a was encoded with QT7.7.1.
QT7.7.0 had serious problem with this sample (very obvious artifact can be heard for each seconds).
This killer sample was found on a Japanse forum, and I have reported this to QuickTime dev before;
It's now fixed in QT7.7.1.
I haven't tried 7.7.1 so much, but currently I have an impression that 7.7.1 tends to output slightly larger result (in file size).