If iTunes is playing back a digital multichannel file format like AC3 (Dolby Digital) or DTS, those bitstreams are wrapped in Apple’s compression and encryption, and then decoded at the other end. In those cases, AirPort Express would end up streaming the raw AC3 or DTS stream via an optical cable to your home theater receiver for decoding.
iTunes can play and output AC3 and DTS? How does that work — and from what source? Are there standalone AC3/DTS audio tracks out there somewhere? I’ve generally only seen them used on DVDs, though I know that there are some audio CDs made that use DTS, and probably some that use AC3. If I had such a CD, how would I put an AC3/DTS audio track into iTunes?
I don’t have a use for this information right now, I’m just really curious. It’s news to me.
iTunes: “Sweet Surrender (Roni Size v2)” by McLachlan, Sarah from the album Plastic Compilation Vol. II (1998, 4:00).