CoreAudio doesn’t provide a means to load and play protected audio files (such as m4p files purchased through the iTunes store), so Neutrino resorts to using QuickTime to play such protected files.
QuickTime is also used in instances where a supplied audio-format isn’t available for use by CoreAudio without additional pre-processing, and of course for all video files.
If you wish to play protected audio files via CoreAudio, the files must first be converted to a non-protected format. iTunes itself provides a way to do so, by allowing the user to burn AudioCD’s from any playlist; the files written to CD will be ‘normal’ AIFF files. AIFF is arguably the ‘best’ format for CoreAudio, as it requires the least amount of conversion and decoding for playback.
Various third-party applications are also available that will allow you to create ‘unprotected’ versions of ‘protected’ files (note that all of the available solutions require you to have the relevant iTunes passwords for the files to be processed).
Note that you will only be able to automatically play protected audio-files registered to the current logged-in user; in cases where the license doesn’t match the registered owner details, you should be presented with an authorisation dialog-box, which will ask you to enter the appropriate iTunes store password before playing the file.
When playing in QuickTime mode, if QT 7.x or later is installed, fixed-pitch rate-shifting should be available on most Macs.