(Updated 15 March, 2008) With the Apple TV 2 update, Dolby Digital 5.1 surround sound in now possible. This post provides information about how to get your system set up for 5.1 surround sound. If any of this is incorrect, I welcome and appreciate corrections by other forum members. As new information becomes available, I will revise this post. 1. Definitions A. Dolby Digital AC-3 (DD). This is usually 6 channels (termed '5.1') that is sent over a digital connection, either by HDMI or optical cables from the Apple TV to a receiver with the respective inputs. The channels for DD are L, R, C, Rr, Lr and the low frequency LFE channel. The LFE is the '.1' channel. B. Dolby Pro Logic II (DPLII). This is a 5-channel surround signal that can be sent over analog or digital connections. The 5 channels are R, L, C, Rr and Lr. DPLII also can be encoded and transmitted over stereo (i.e., 2 lines, right and left) cables to a receiver that is capable of decoding the signal and outputting to all 5 channels. C. Dolby Pro Logic (DPL) (and Dolby Surround, DS). This is a 4-channel surround signal that can be sent over analog or digital connections. The 4 channels are right (R), left (L), center (C) and rear (r - two signals Rr and Lr, but it is mono so only counts as one channel). DPL can be encoded and transmitted over stereo cables to a receiver that is capable of decoding the signal and outputting to all 4 channels. In Apple TV files DPLII, DPL, DS and stereo are encoded in AAC tracks. You can read more about these from the pulldown at Dolby's surround sound web page. http://www.dolby.com/resources/tech_library/index.cfm 2. Hardware A. Apple TV. The Apple TV has three means of delivering audio: over the HDMI cable, through its optical port, and through its two channel RCA jacks. While the HDMI and optical port can deliver both digital (DD) and analog (DPL, DPLII, DS, stereo), the RCA jacks can only deliver analog audio. B. TVs. Many new TVs have inputs for HDMI and optical cables, as well as analog RCA jacks. However, most only decode Dolby Digital delivered through their ATSC tuners (e.g., over-the-air antenna, satellite or cable connections). They generally are unable to decode DD from other hardware sources, such as an Apple TV or DVD player. In addition, they cannot passthrough DD from a device to a receiver; the TVs can only pass analog audio to the receiver. The exception to this rule is the built-in ATSC tuners that all new TVs have. These connections from a TV to a receiver are HDMI, optical cable or coaxial cable, each of which is capable of delivering digital audio information to the receiver. C. Receivers/Amps. Most receivers today have the ability to receive and decode Dolby Digital audio (and DTS digital audio, but which will not be discussed since the ATV2 does not do DTS). The least expensive units have optical and/or coaxial digital audio inputs, often more than one, while the more expensive units have these inputs as well as HDMI inputs. In addition, some of the receivers with HDMI inputs also have HDMI outputs and can be used to control your video as well. These HDMI receivers are able to provide DD 5.1 surround while also passing along video to your TV. 3. Software A. Quicktime Player. With the release of the Apple TV 2 update, Quicktime for the ATV2 saw an update with the ability to passthrough AC-3 Dolby Digital (e.g., 5.1) surround sound, provided the movie file has such a track and that a receiver capable of decoding DD is connected directly to the ATV. This feature of autoselecting audio tracks in ATV's Quicktime apparently is not available for Macs, although Quicktime on Macs can passthrough AC-3 DD if the track is enabled (and with DVDs and DVD Player app). B. Handbrake. With the release of version 0.9.2, Handbrake included the ability to encode videos with both AAC (analog) and AC-3 5.1 (digital) surround sound, provided your source DVD has 5.1 surround sound tracks. By choosing the "Apple TV" preset in Handbrake, you get both audio tracks, with the AAC turned "on" and the AC-3 turned "off" by default. (This is also how the high-def with DD movie rentals from Apple are arranged, too.) The new Quicktime that ships with the ATV2 update automatically determines if (1) the movie file has an AC-3 track and (2) if your receiver is capable of decoding AC-3 audio. If both conditions are true, then the ATV will enable the AC-3 track. Otherwise, the ATV will only use the AAC track as the audio source. 4. Connections A. Non-HDMI Receiver. If your receiver does not have HDMI inputs, then your best solution is to connect your Apple TV to your TV by its HDMI cable or component cables, then use a Toslink cable to connect your ATV to your receiver. You cannot connect your Apple TV to your TV with HDMI or optical cable and expect your TV to passthrough DD 5.1 to your receiver. The receiver must be connected directly to the ATV by optical cable. The audio can only be passthroughed once (but video can be passed at least twice). This is because of Digital Rights Management issues. If your TV does not have HDMI and you are using the component video connections from your ATV, then you should also connect your ATV audio to your TV using the RCA audio jacks. B. HDMI Receiver. If your receiver has HDMI inputs, connect your ATV to it using an HDMI cable. You then need to connect your receiver's video-out to your TV, either by HDMI, component or composite cables. In this way, you will get DD 5.1 surround sound. C. Listening to audio without having your TV on. If you listen to music, audio books or audio podcasts with the ATV, you may not want your TV on while using these media. If your RCA jacks on your ATV are unused, you can connect them to your receiver in such a way that it is unnecessary to leave your TV on while listening to audio media. For my setup, I have our ATV connected to our TV by HDMI, and to our Onkyo receiver by its optical cable. Because the RCA jacks on our ATV were unused, I connected them to the "CD" input on the receiver. With this setup, I set the receiver to CD mode, then start a music playlist from the ATV, then turn off the TV. The music continues to play until the last song. See this post for the break in this thread between ATV2 and ATV1. ******************************************************* * The information below is the original post and applies to * pre-ATV2 only. If you still use versions 1.0 or 1.1, you should * use this information. ******************************************************* OK, I'm going to try to clarify audio on an Apple TV versus a Mac Mini. I hope to be clear and accurate, but your mileage may vary. I'm only going to discuss Dolby Labs' technology, and not DTS. I am no expert, but this is the information I've manage to pull together. If any of this is incorrect, I welcome and appreciate corrections by other forum members. As new information becomes available, I will revise this post. 1. Definitions Dolby Pro Logic (DPL) (and Dolby Surround, DS). This is a 4-channel surround signal that can be sent over analog or digital devices. The 4 channels are right (R), left (L), center (C) and rear (r - two signals Rr and Lr, but it is mono so only counts as one channel). DPL can be encoded and transmitted over stereo (i.e., 2 lines, right and left) cables to a receiver that is capable of decoding the signal and outputting to all 4 channels. Dolby Pro Logic II (DPLII). This is a 5-channel surround signal that can be sent over analog or digital devices. The 5 channels are R, L, C, Rr and Lr. DPLII also can be encoded and transmitted over stereo cables to a receiver that is capable of decoding the signal and outputting to all 5 channels. Dolby Digital AC-3 (DD). This is usually 6 channels (termed '5.1') that is principally sent over a digital connection, such as a TOSLINK optical cable from the Mac Mini or Apple TV's optical audio port (but is currently nonfunctional on the ATV because of software limitations) to a receiver. The channels for DD are L, R, C, Rr, Lr and the low frequency LFE channel. The LFE is the '.1' channel. You can read more about these from the pulldown at Dolby's surround sound web page. http://www.dolby.com/resources/tech_library/index.cfm 2. Hardware Apple TV. It has an audio chip that can decode up to a 7.1 signal. It has both optical audio out (which is capable of delivering a DD signal, but currently is not implemented) and RCA stereo jacks (which are analog and can thus deliver DPL or DPLII, but not DD, signals). The Apple TV uses Quicktime to play its video content and encoded AAC audio (which is distinct from AC-3 audio). It does not have DVD Player application that ships will all Macs. Mac Mini. I do not know what the audio chip is inside the Intel-based Minis, but it is capable of at least 5.1 audio passthrough using its optical audio-out port (which is also a dual-function analog stereo-out port). If you connect a TOSLINK cable to it you get optical output (DD, DPLII, DPL, DS, Stereo). If you connect a 1/4" stereo to RCA cable to it you get analog (stereo, DPL, DPLII, but not DD) output. The Mac Mini can use Quicktime or DVD Player to play video content, depending on the file type. 3. Software DVD Player. This program on the Mac Mini is capable of sending Dolby Digital AC-3 audio data through the optical port of a Mac Mini via a TOSLINK cable. It cannot send AC-3 out via a stereo-to-RCA cable. If you play a DD 5.1-encoded DVD (real or ripped to your hard drive with MacTheRipper) using DVD Player and you have a TOSLINK cable between your Dolby Digital-capable receiver and Mac Mini, DVD Player will passthrough the AC-3 info to the receiver, which will decode it into all 6 channels (L, R, C, Lr, Rr, LFE). This will give you 5.1 surround sound. If the DVD only has DPL, DPLII or 2-channel stereo, then only those can be passed through. You cannot get 5.1 surround from DPLII, DPL or stereo audio. Quicktime Player. The program is found on the Mac Mini as well as the Apple TV. Since it cannot decode AC-3 audio files, there is currently no way to get AC-3 audio (i.e., 5.1 surround) from Apple TV to a 5.1 receiver. Quicktime is capable of encoding 6 discrete audio channels, but they are in AAC, not AC-3. Since there are no consumer receivers on the market that can decode AAC, you cannot get 5.1 surround sound from the Apple TV or Mac Mini using Quicktime. Quicktime will, however, allow the playback of stereo and since DPL and DPLII can be encoded in stereo channels you can get 4-channel (DPL) or 5-channel (DPLII) audio from your Apple TV or Mac Mini, provided they are connected to a receiver capable of decoding DPL or DPLII. (Note, though, that there is usually channel leakage in DPL and DPLII, thus separation is not as good as it is with DD.) Handbrake. With the release of version 0.9, Handbrake included the ability to convert DD AC-3 into DPLII 5-channel surround in the transcoded Quicktime video file. If you select the Apple TV preset for a DVD with 5.1 AC-3, Handbrake will convert the 5.1 AC-3 file into a DPLII stereo audio track (see "Track 1 Mix" on attached screen shot) of the H.264 output MPEG4 file and it will contain the L, R, C, Rr, and Lr channels, but not the LFE channel. If you play this on the Apple TV using a TOSLINK cable (or the RCA jacks) to connect the ATV to your DPLII-capable receiver, you will get 5-channel surround (but not 5.1 surround). Handbrake also has a provision to convert the 5.1 AC-3 audio into 6 discrete channels encoded in AAC in Quicktime; however, as mentioned above, since there are no consumer receivers on the market today that can decode AAC from Quicktime audio there's really not much point in using this feature of Quicktime. I have tried this, and it does play on my Onkyo receiver, but it is not 5.1 surround. VLC. Handbrake can also be used to transcode DVDs into MKV format containers with H.264 video encoding and Dolby Digital AC-3 5.1 surround sound passthrough (see second attachment). These files will not play in Quicktime, thus cannot be used for playback on the ATV. However, VLC will play them on a Mac and passthrough the AC-3 audio file through the optical port to a receiver using a Toslink cable. (Install Perian for good measure.) Provided your receiver has an optical input and the ability to decode Dolby Digital, you can get 5.1 surround sound with your movies. One word of caution: VLC is very buggy and skipping ahead can cause all kinds of problems with crashing VLC, and also crashing your audio in such a way that the only fix is to reboot your Mac. In addition, these files are typically much larger than MP4 H.264 stereo/DPL/DPLII files because of the size of AC-3. A 2 gig movie with MP4/DPLII will be about 3 gigs as an MKV/AC-3. DVD2OneX. DTOX is an app that will take a DVD ripped to your hard drive with MacTheRipper and compress it to a smaller size. One preset is to make it small enough that you can fit it on a single-layer DVD. You can use it to clone the DVD or to make a DVD for individual videos from the DVD. If you have Leopard on your Mac, Front Row will now allow you to play DVDs from your hard drive. Because of this, I have my 5.1 surround sound-intensive DVDs MTR/DTOX'd to 4.2 gig VIDEO_TS folders for playback on my Mac Mini home theater system. Its much cleaner and reliable than playback of MKV files with VLC. I have an external firewire drive with a folder called 'DVD' in which these VIDEO_TS folders are stored, and an alias to the DVD folder is copied to my Home/Movies folder. When Front Row is launched, select Movies, then drive down to the DVD folder of your choice. Of course, these ripped VIDEO_TS folders can also be played by DVD Player with passthrough of the 5.1 surround sound to your receiver, as well.