QuickTime doesnâ€™t come with an [tag]AC-3[/tag] codec by default. There is an open-source QuickTime component available, called A52Codec, which enables QuickTime to open, import and export AC-3 audio. (It does this using a free AC-3 library called liba52.) A52Codec provides some form of support for working with AC-3 under QuickTime, at least for file conversion and export. What the A52Codec canâ€™t do, however, is to enable applications to stream encoded AC-3 data straight to the optical output on the Mac.
Appleâ€™s DVD Player application – included for free on every Mac – can play the 5.1 AC-3 audio from a physical DVD directly through the optical output of your Mac. DVD Player does this by streaming the encoded AC-3 straight from the DVD to the optical out, bypassing QuickTime. Some other players – notably VLC (which also uses liba52) – will stream AC-3 straight to your optical output, too. But any application which uses QuickTime for its audio playback – and this includes Front Row, iTunes, and QuickTime Player – works by first decoding audio into its discrete channels, before outputting it to your system audio device. The AC-3 encoding is lost in the process. So if you want a Mac Mini and Front Row to run your home theatre, with 5.1 sound from third-party movie files, then itâ€™s not so easy.