There are a couple of ways at the moment to get true 5.1 audio out of your AppleTV and there are non-trivial caveats to each. If, however, you are comfortable with the 5.0, non-discreet surround provided by Dolby Pro Logic II then you are already good to go. I'll discuss the various options for surround sound as well as their pros and cons below:
1. Get true, 5.1 discreet audio by hacking your AppleTV
There are a few documented ways to hack your AppleTV, you can find them on AkwardTV. The easiest way, which does not require the removal of the AppleTV's hard drive, still requires some significant computer knowledge and isn’t perfect. Once you have your AppleTV properly hacked you are then free to install Perian and add new plug-ins to the AppleTV interface such as ATVFiles. Perian is a QuickTime component that allows for the playback of many audio and video formats not supported by QuickTime by default including (in more recent builds) AC3 audio. ATVFiles is an AppleTV plug-in that allows you to play files on your AppleTV that are not in the iTunes database such as the .AVI or .MKV files that can contain an AC3 audio track. Once you have these tools installed you can use HandBrake to encode your DVDs using the AVI container with AC3 audio as the soundtrack. AC3 is the audio container used by DVDs and it holds the 5.1 Dolby Digital or DTS soundtrack you’re looking for. Also, your receiver along with most receivers made in the past several years can decode what’s in your AC3 stream into discreet 5.1+ channel digital audio.
- - Once you get everything working properly you can watch your movies with the exact same audio experience as you have on the original DVD.
- - Hacking the AppleTV can be troublesome / impossible for novices.
2. Get true, 5.1 discreet audio by tricking iTunes
- - The ATVFiles interface doesn’t provide the eye-candy of the default Movies interface with movie art, descriptions, directors, ratings, etc.
This method allows you to get the discreet, 5.1 digital audio you’re looking for without hacking your AppleTV while keeping both the AppleTV Movies interface as well as the management of your library through iTunes. Sounds perfect, right? Well, it’s a pain in the ass. The exact method and steps required are discussed at length in this forum topic so I won’t repeat them in detail. Glossing over the process, you first encode your movie with HandBrake using an MP4 container. Then your use a tool that strips the AC3 audio track from the DVD and another to transcode the AC3 into a DD-WAV. Then you use QuickTime to encode the DD-WAV into ALAC (Apple Lossless). Finally, you open your movie’s .MP4 file in QuickTime, delete the audio track inserted by HandBrake, insert the ALAC audio soundtrack, and save to a .MOV file. Potential stumbling blocks include audio possibly being out of sync and that this trick only works with a 44.1khrtz audio and not the usual 48khrtz found on DVDs so there’s an extra step in the process of doing that conversion. Once you get a movie made this way you’re all set.
- - You get a true, discreet 5.1 channel audio experience from your movies (though, arguably, with a very slight loss in quality)
- - You get to manage your movies through the default iTunes and AppleTV interfaces
- - The creation process is onerous at best.
- - Your movies can only be played by an AppleTV connected to a receiver. Connecting your AppleTV directly to a television would result in screeching audio static because a TV can’t decode the digital audio stream.
3. Get non-discreet, 5 channel audio through HandBrake and Dolby Pro Logic II
- - File size is increased by 300-400 megabytes due to the lossless audio
This method is far and away the easiest. Open your DVD with HandBrake, select the HB-AppleTV Preset, and click Start. Again, I glossed over potentially important stuff like checking for deinterlacing, changing audio bitrate, different x264 options, etc. but those are all things you’d need to fool with in the other options as well. The result is a movie, like the movie from option 2, that works with both the AppleTV and iTunes interfaces. You get all your movie art, descriptions, etc. and you can play the movie from your AppleTV connected to any device, not just a receiver, since the audio track is just a specially encoded stereo track. Your Dolby Pro Logic II capable receiver, however, will be able to pull out 5 channels of sound from that stereo signal. You get center, left, right, left-rear, and right-rear channels of audio but you lose your LFE (subwoofer) channel. Also, since this isn’t discrete audio you get some bleed from other channels into the proper channel, some of the left channel might be heard in the left-rear channel for instance. Further, the separation is noticeably more muddy due to the non-discreet nature of the audio. But, hey, it’s easy and it works!
- - You get a definite surround sound experience
- - It’s very, very easy to use. If you can run HandBrake you can make Dolby PLII movies
- - You get to manage your movies through iTunes and the AppleTV Movies interface
4. Encode with AAC 5.1 and pray that Apple will one day upgrade the AppleTV software to do AAC 5.1 to AC3 transcoding on the fly
- - It’s a surround experience, yes, but it doesn’t compare to true, discreet audio. Listen to a Dolby PL II track right after playing the same track in AC3 and the superiority of AC3 will be clear as day.
This method is as easy as encoding with Dolby Pro Logic II, you just select AAC 5.1 as the audio track in HandBrake. You end up with a movie that contains 6 discreet audio channels (center, left, right, left-rear, right-rear, and LFE) and a movie that is manageable via iTunes. The movies will be accessed through the AppleTV Movies interface but it’s not that great because iTunes won’t append metadata like art, descriptions, directors, etc. to movie files with more than one audio track so you end up with one of the first frames from the movie as your cover art and no description, etc. Worse, the AppleTV sends the AAC 5.1 track out as a stereo signal but not one encoded with Dolby Pro Logic I or II in mind so your receiver has to make due with what it gets. The result is an audio experience more akin to Dolby PL I but nowhere near as good as what you get from using the Dolby Pro Logic II encoding option in HandBrake. The reason one would encode this way is in hopes that Apple will one day upgrade the AppleTV to transcode AAC 5.1 into AC3 on the fly as well as update iTunes to allow appending metadata to these files. Certainly, if Apple made these changes we would be in movie encoding nirvana. However, it’s a big gamble to start encoding your movies with this eventuality in mind since, despite circumstantial evidence, there’s no proof Apple has plans to ever make these changes.
- - Your movie is encoded with discrete digital audio (even though you can’t play it that way)
- - Very easy to use, as easy as the Dolby PL II option
- - A very marginal surround experience (for now)
- - You don’t get any metadata with your movies
Obviously, the surround audio situation with the AppleTV is not ideal. In lieu of waiting around for everything to be perfect I’ve embraced maurj’s Dolby PL II implementation for my movies as it provides the best audio separation vs. ease of use ratio available but I’m only adding my older movies to my AppleTV library, movies that either don’t have a 5.1 track to begin with or don’t suffer by losing the true 5.1 experience. So any recent action movie is ruled out by my methods but I’m left with many dramas and most comedies to encode while I wait for improvements in AppleTV or HandBrake.
Let me finally mention that there is more involved with the first two steps I explain than what I’ve written down. If you intend to take either of those routes you would do well to read articles at AwkwardTV and also articles linked from earlier in this topic thread to get a better understanding of what you’re actually doing. Also, to get the most out of the open source software used to make these options available you should use more recent builds of both HandBrake and Perian than what is available as a binary download from their respective sites and that means downloading source and compiling yourself.