While I believe what you guys are saying, that doesn't explain the fact that my receiver displays 'DTS' during the intro movie and the DTS logo lights up (just as if I were playing a bluray or something with a DTS soundtrack). If you really don't believe me I'll take a picture of it or something. Strange...
My Onkyo receiver illuminates the DD symbol with the startup video. Something about your receiver, I suspect, unless you've managed to disable DD out on your ATV.
As far as this AAC/AC3 discussion, I don't know what AAC is.
AAC is the 'analog' audio that is part of the MPEG-4 standard. All iTunes video and audio files use it.
All I know is that purportedly most HD movies that you can rent on ATV are supposedly capable of playing in Dolby Digital (5.1 discrete channels).
All of them have AAC audio as track 1. If they have digital audio they will have the double-D emblem denoting Dolby Digital (AC3) or explicitly state Dolby Digital 5.1.
When playing one of these movies, my receiver (up until this week) displayed 'DD 5.1' (or DD EX 7.1 if I so chose), and now it doesn't; it can only be set to Pro Logic II.
None of them come with 7.1, which would be Dolby Digital Plus (E-AC3). AAC is a two-channel matrix that can contain Dolby Pro Logic II (up to 5 channel surround). Since it was working for you before, there must be some setting issue on your receiver that has been changed.
That can't be correct. Apple states on the AppleTV and iTunes websites that many HD titles come with Dolby Digital 5.1 surround. Therefore they must have an AC3 encoded track, right?.
The purchased or rented
TV shows and movies can have AC3 Dolby Digital (and all have AAC audio), but
none of the trailers have AC3 (not even the HD trailers); they all have AAC audio tracks.
Further, this used to work. I've rented HD movies on ATV that DID have AC3 surround as indicated by the receiver's DD 5.1 display. When I rented an SD movie or an HD movie without the Dolby logo in its info page listing, the receiver just used Pro Logic II. Now it uses Pro Logic II even for movies which have the 'double d' logo that's supposed to indicate an AC3 track. The question is what would cause this to stop working and how might I fix it.
I can't help you there (I assume you have Settings > Audio & Video > Dolby Digital enabled on your Apple TV). I haven't rented an HD movie from iTS since the early days of the 2.0 update, and I've never bought one. When I did rent
Live Free Or Die Hard, it had AAC audio for track 1 and AC3 audio for track 2. All of my DVDs and Blu-rays have been transcoded for the Apple TV with AAC audio on track 1 and (when available) AC3 on track 2.