Apple has clarified the details of high-defintion movie rentals with the new Apple TV software. Things are a little different compared to how users are accustomed to buying movies and TV shows within iTunes on their Mac.

iPO asked Tom Neumayr at Apple about how the HD movie viewing works. It’s an item that has been glossed over compared to the traditional method of viewing iTunes content on a Mac, and some customers may have been confused.

First, HD movies are availble only for rental. While SD movies can be purchased, HD movies cannot. The rental operation is initiated on the Apple TV’s onscreen display on the HDTV, not on the Mac.

Second, the Apple TV streams the movies directly from Apple servers. Of course, a very good broadband connection is required. The movies are streamed, and not downloaded to the Apple TV first. Within a few seconds, the movie will start to play. How much compression of the HD movie occurs to achieve this is not yet known, and iPO will report on this when more details are known.

Because the HD movie is streamed and output directly, via HDMI to the user’s HDTV, it cannot be saved/synced back to a Macintosh or even viewed there. It’s likely that these conditions were set by the studios to protect HD movies from ever residing digitally on the Apple customer’s Apple TV, being unlocked, and possibly pirated.