So does the Apple TV support 5.1 audio?

No. And yes. In that order. This article gives the full detail behind what that really means.

A little while back, I posted an article discussing the possibilities for the Apple TV supporting 5.1 audio playback. It’s well worth reading that article first, as it talks a little bit about what “5.1 playback” actually means. Now that the Apple TV is available, and I’ve been able to run some tests, I’ve been able to see what it can and can’t do. It’s a mixed bag of news; not as good as expected, and a little surprising, too.

There are a few different scenarios here, based on what kind of “5.1″ you’re trying to play:

1) You might have a movie file with a Dolby Pro Logic I (that’s I for one, not II for two) soundtrack.1 DPL I supports the matrix-encoding / decoding of 4.0 channels of audio into a stereo source. Note that this isn’t a four-channel (4.0) soundtrack. Rather, it is a stereo (2.0) soundtrack, with a set of 4.0 audio information matrix-encoded into the stereo track. The four channels you get are Left, Center, Right and Rear (where Rear is a mono “surround” channel for a rear speaker).

Play a DPL I track through a 2-channel device, and you’ll hear the audio, just in 2-channels only. Play it through a DPL I-savvy amp, and the 4 tracks will be un-matrix-encoded into their four separate channels.

Importantly, this is the audio format used for movies from the iTunes Store. So right now, iTunes Store movies aren’t even 5.1 – they’re 4.0.

2) You might have a movie file with a Dolby Pro Logic II soundtrack. Note that similar to DPL I above, this isn’t a six-channel (5.1) soundtrack. Rather, it is a stereo (2.0) soundtrack, with a set of 5.1 audio information matrix-encoded into the stereo track. The six matrix-encoded channels are made up of five normal channels (Left, Center, Right, Left Surround, Right Surround), and one LFE (Low Frequency Effects) channel. These are the 5 and the 1 in 5.1.

Play a DPL II track through a 2-channel device, and you’ll hear the audio, just in 2-channels only. Play it through a DPL II-savvy amp, and the 6 tracks will be un-matrix-encoded into their six separate channels. (Actually, the LFE is really just the low frequencies in the Center channel, but that’s too much detail for here.)

You’re unlikely to have a movie with a DPL II soundtrack, unless you’ve ripped an existing one from a DVD using a tool such as Handbrake.

3) You might have a movie file with a Dolby Digital soundtrack (also known as an AC-3 soundtrack). (Note that AC-3 and AAC are not the same thing.) It’s unlikely you’ll have an AC-3 soundtrack, as QuickTime can’t play these tracks (see my previous article for more information on this). However, DVD conversion tools such as Handbrake can copy Dolby Digital AC-3 tracks straight from a DVD into an avi file, so you may have got one this way.

4) You might have a movie file with a 6-channel AAC soundtrack – such as one of Apple’s high-definition movie trailers. These soundtracks have six discrete audio channels – one each for Left, Center, Right, Left Surround, Right Surround, and LFE (Low Frequency Effects). Each channel is encoded in AAC format.

To play a 6-channel AAC file on a Mac, you would need an audio device with six discrete audio outputs (such as the Griffin FireWave). This will only work with a Mac, as you can’t add external audio devices such as the FireWave to the Apple TV.

It’s unlikely you’ll have one of these soundtracks, unless you’ve downloaded one of the Apple HD trailers. (However, a future version of Handbrake is rumoured to be able to extract a DVD’s 5.1 AC-3 to 6-channel AAC.)

That covers our starting points. On to the tests.

The first major observation is this: it seems that whatever the Apple TV can do, QuickTime can do too. This perhaps isn’t a major surprise – after all, I’d assumed that the Apple TV would be running some flavour of QuickTime 7.1 – but it does make the observations more interesting. More on this later.

So, onto 5.1. According to Gizmodo, Apple claims that the Apple TV “supports 5.1″. Whether this claim is a genuine claim from Apple (or not) is neither here nor there. What is clear from my tests is that the only form of 5.1 supported by the Apple TV is Dolby Pro Logic II – and it isn’t really working too hard to provide this support.

If Apple are saying “we support 5.1″ to mean “we support Dolby Pro Logic II”, what they really mean is:

“If you have an existing QuickTime-friendly movie with a stereo soundtrack, which happens to have Dolby Pro Logic II 5.1 information matrix-encoded into it, then we’ll happily play that stereo soundtrack to your amplifier. If your amplifier then happens to detect and decode the Dolby Pro Logic II encoding, then you’ll get 5.1 sound out of your speakers.”

Or, to put it another way:

“If you’ve got a stereo soundtrack, we’ll play it for you.”

Thanks, Apple TV!

The same principle goes for the 4.0 audio encoded into a Dolby Pro Logic I soundtrack, and this is how iTunes Store movies are providing their “surround sound” audio right now. All the Apple TV is doing is playing the stereo signal to your amplifier, over the Apple TV’s optical output. Your amplifier then decodes the 4.0 DPL I audio from this stereo signal.

To refer back to that QuickTime reference above – this is also true of QuickTime Player, iTunes, and Front Row on a Mac, too. Plug your Mac’s optical output into an amplifier, and the same thing holds true.

So that’s scenarios 1) and 2) covered. What about 3), where we have a proper Dolby Digital track? Simply put, the Apple TV won’t play these encoded Dolby Digital AC-3 tracks any more than QuickTime on a Mac will. So true, pure Dolby Digital 5.1 just isn’t there right now.

But here’s an interesting thing. In scenario 4), the Apple TV does something unexpected. Rather than downmix the six discrete AAC channels to a simple stereo mix – splitting Center between Left and Right, mixing Left Surround into left (likewise Right Surround into right) and ignoring LFE – it actually seems to be doing some matrix encoding of its own. It’s not quite Dolby Pro Logic I, and seems to be more of a 3.0 mix rather than a 4.0 mix. But it’s definitely more than stereo.

Here’s what the AppleTV (and also a Mac with QuickTime 7.1.5) outputs when playing a 5.1 AAC track via an optical cable, with my amplifier set to expect Dolby Pro Logic I:

The Left channel plays through the Left speaker, and (quietly) through the Left and Right Surround speakers
The Right channel plays through the Right speaker, and (quietly) through the Left and Right Surround speakers
The Center channel plays through the Center speaker only
The Left Surround channel plays through the Left speaker, and (quietly) through the Left and Right Surround speakers
The Right Surround channel plays through the Right speaker, and (quietly) through the Left and Right Surround speakers

My reading of this is that the Apple TV is matrix-encoding the center channel into the stereo output when playing a 5.1 file, and my amp’s Dolby Pro Logic I setting is successfully decoding this as a separate Center channel. The Apple TV is mixing down the Left Surround signal into the Left channel, and likewise Right Surround into the Right channel, and my amp is playing these to the Left and Right speakers. The Dolby Pro Logic I setting on my amp is then also trying to extract a Rear channel, but is failing to find one, which is why a quiet version of Left / Right / Left Surround / Right Surround is playing through the Left / Right Surround speakers.

It’s a bit of a surprise to hear the separate center channel from a 5.1 AAC source, and it’s definitely more than I would have expected from Apple TV (and QuickTime). It’s interesting in itself that the Apple TV will ‘play’ 5.1 soundtracks at all (as a video iPod won’t play a 5.1 AAC soundtrack), and more so that it seems to be doing this matrix-encoding for the center channel. Most likely this is because behind the scenes it’s really a kind-of-Mac-Mini, running a kind-of-QuickTime, rather than a kind-of-iPod.

What’s disappointing is that the Apple TV doesn’t feature any way to play “true” 5.1 Dolby Digital AC-3 tracks – most likely because it is based on QuickTime, which can’t play them for the reasons described in my previous article. Even more disappointing is that it won’t encode 5.1 AAC tracks to AC-3 on the fly, most likely because this would involve licensing Dolby Digital Live from Dolby themselves, with an associated cost. And until the iTunes Store starts shipping movies encoded with Pro Logic II (rather than Pro Logic I), then the average user will be getting 4.0 at best from movies they buy from Apple to play on their Apple TV.

This seems to be indicative of the general approach taken by Apple with the Apple TV – i.e. make it good enough that most people will be happy with the playback it is capable of, whilst keeping it affordable enough that most people will want to buy it. For anyone wanting high-quality audio, it’s a shame that Apple didn’t make more of the opportunity, even if it meant paying Dolby some money. The same could be said of its video capablilities – 720p rather than 1080p – good enough for most people’s needs, whilst not satisfying the AV purists. Still, Apple’s success with the iPod suggests that they’re pretty clued up when it comes to knowing the right feature set to hit – and Apple’s “good enough” is usually still pretty good :-)

Of course, this could all change with a software update… here’s hoping that any extra features for the Apple TV will make it into QuickTime too.

Update: I worked out why the Apple TV (and QuickTime) are outputting a center channel to my Pro Logic amp. It’s not surprising at all, once you learn a bit about how Dolby Pro Logic works.

When QuickTime mixes down the 5.1 AAC to stereo, it splits the “center”2 input track equally between the left and right output tracks. After all, what else could it do with “center” but share it between “left” and “right”?

Here’s the twist. It turns out that this is precisely how Dolby Pro Logic I and II matrix-encode their center channel too. The Dolby Pro Logic decoder in your amp is looks for any audio which appears in both the left and right channels of the input, and extracting this as a center channel to be sent to your center speaker. So, QuickTime is inadvertently causing a Dolby Pro Logic-friendly 3.0 matrix-encoded mix when it mixes 5.1 down to stereo. Thanks, QuickTime!

Update: Good news – the latest version of HandBrake, version 0.8.5b1, features an option to convert 5.1 AC-3 tracks into a 5.0 matrix encoded Dolby Pro Logic II track. This is playable by the Apple TV (as described above), and looks like the best way (currently) to play surround sound on your Apple TV.

Handbrake 0.8.5b1 also now has the ability to convert a 5.1 AC-3 source to a 6-channel AAC, as mentioned above.

1Strictly speaking it’s encodedwith Dolby Surround, and decoded with Dolby Pro Logic. But this quickly gets very confusing, so I’ve used Pro Logic I / Pro Logic II to differentiate between the 4.0 and 5.1 versions of Dolby Surround / Pro Logic.

2Yes, I know – I’m British, and should be “centre”, not “center”. But I’ve been coding HTML since 1994, and these things stick.

31 thoughts on “So does the Apple TV support 5.1 audio?

  1. Awesome write-up, thanks. I was just in the Apple store today asking about this stuff. It became apparent very quickly the guy didn’t really know anything useful. And yes, it’s very disappointing. Would have been nice if they had the “Good” & “Better” options so that you could pay a bit more for one that had licensed the Dolby Digital. Maybe next rev.

  2. Good article, have you tried passthrough 5.1 DTS encoded audio to a DTS decoder/preamp?

    For example the airport express CAN pass through 5.1 DTS disc (www.dts.com) content to be decoded by an external DTS decoder/preamp. The DVD-Audio 5.1 DTS discs must be ripped into a lossless format and then played/streamed from iTunes with no modifications (no EQ or Volume adjustments.) The digitally (optical or copper) connected preamp decodes to 5.1 properly and controls the volume. Phenominal experience…

  3. Paul,
    I don’t have a Mac Mini to test with, but from my tests on a MacBook Pro, the results are identical. I see no reason why the same shouldn’t be true for a Mac Mini.

    Parr,
    I’ve not tried DTS extraction like this; but I’ll give it a go!

  4. Did you test the standard AppleTV, I would think that if you add on the codecs for avi containers AC-3 Audio and all of that it might play it back in its original form, am I wrong or if all the codecs are there I think it should or would??

  5. I really enjoyed your two artices in this series. Very informative! I thought you might want to check out this article written about the subject which (as far as I can tell) supports your conclusions and raises an additional interesting point: were manufacturers to support 5.1AAC in the future, all our problems would be solved! What do you think? Article link is http://www.roughlydrafted.com/RD/RDM.Tech.Q1.07/147048D8-D8B7-45E7-9A97-3CD5B4C2B75A.html

  6. There’s a reason why everyone mentions discrete channels. Pro Logic, as you said, does not offer discrete channels. It can only take the sound at that moment (L or R channel) and direct it to a particular speaker. I presume it could do L or R independently. It’s a very limiting and disappointing system compared to discrete channels.

    Like you said, it would be awesome if something (AppleTV would be best!) would transcode the incoming discrete audio to a common discrete format supported by most amps (7.1 would be my preferred — if the source has it; DTS would be great too or Dolby Digital.) If it requires licensing DD Live then so be it.

    This is rev 1.0. If the hardware is good enough, they might be able to offer a software update later to do transcoding but my bet is that’s a selling feature later — if the AppleTV takes off.

    Alex, I would hope that future amps do support MULTI-track AAC in the future — up to the number of channels the amp can do. Thanks for the RD link. Great info.

  7. Wow! Great article! Very informative and finally I got some answers to questions I had ever since FrontRow came out with the G5 iMac.
    Thank you!

  8. Great articles. I have one thing to add though. You discuss Dolby Digital and AC-3 in depth but have not mentioned DTS. I can play a DTS 5.1 bitstream through AppleTV, either from the internal HD or streaming from iTunes. Unfortunately these are sound files only, and not a DTS coded Feature. I’m looking forward to AC-3/DTS Features from the Itunes Music Store.
    NOTE: DTS is sonicly a better sound signal, by using a higher bitrate than Dolby Digital.

  9. You don’t mention audio output through HDMI. The HDMI is capable of carrying 8 channels of uncompressed PCM audio. Therefore, if you have a 6 channel AAC source, such as an Apple HD trailer, there is no reason the AppleTV cannot output it as 6 channel PCM through HDMI and played through a receiver with HDMI input. This is, after all, what HD-DVD and Blu-ray players do DD+, DDTrueHD etc

  10. I dont get this, VLC can passthru AC3, why is it so hard to design a Quicktime plug’in to pass AC3 to another app out side of Quicktime to pass the AC3 stream to the SPIDIF port? Or has no one thought of this?

    Also, the Perian plug in that allows our Handbrake’d movies to play in QuickTime (therefore Front Row) would also need to be updated to support the new Anamorphic video.

    Then we would be talking Mac Home Theatre…

  11. Pingback: Asteroid » Blog Archive » A week with the Apple TV

  12. Assuming one lives in the Netherlands or is hell bent on challenging the DMCA in court what is your advice on backing up ones DVD collection in a format which maintains the highest audio quality and greatest future compatability? Assume H.264 for video.

  13. I’ll be more direct, Apple’s support of 5.1 sucks majorly. Three minor observations:

    a) Handbrake is great unfortunately it only works with DVDs, so no way to convert other AC-3 sources to DLP2 which appears to be the only 5.1 format AppleTV/iTune are capable of handling at this point in time. Or is there another app that will transcode AC3 to DLP2?

    b) As of roughly one month ago VLC was able to feed AC3 5.1 streams directly to optical output. It appears Apple disabled this recently. Thus nothing but Apple’s own DVD player can feed AC3 5.1 now to the optical. Shame on Apple.

    c) It is instructive to download a 5.1 DTS files (another 5.1 format) (e.g. http://www.diatonis.com/downloads/diatonis_dts_wav_io_afos.zip) to see how Apple computers handle them. The results are disaster. My QTP will report them as 2ch stereo files and will output them as such in DTS on optical. iTunes will not be able to play them (static pretending to be DLP instead will be heard on your receiver). VLC will play them “correctly” but only in stereo and as a DLP stream.So it appears there is no way to play DTS 5.1 streams on Macs these day unless you play DTS encoded DVD in DVD Player.

    This sucks.

  14. Gregori, I am not sure what you are talking about. Nothing about VLC audio playback has been “disabled” by Apple or anybody else. I have the latest version of VLC and OS X 10.4, and both Dolby Digital and DTS files play perfectly in discrete 5.1 via optical output.

    Perhaps you forgot to go into the VLC preferences and turn the “Use S/PDIF if available” checkbox on.

  15. Gregori (?) I’m not, that aside T… was right, I forgot to switch VLS to “encoded optical output”. Apparently when I did it long time ago it took, but somehow that was undone recently and I have to redo that setting each time I start VLC. Major pain in a.

    Also I use Skype USB phone and VLC will sometimes redirect the 5.1 output to that device and strangely I can hear it on that mono channel device. The only way to recover VLC ability to output encoded 5.1 to the optical is to: quit VLC, umplug the phone, reset default output in Audio MIDI setup to 2ch encoded, and start VLC again switching it manually to encoded optical. Given this the support of 5.1 on iMacs is still more than problematic as I claimed before.

    P.S. Still looking for a mac utility to convert standard 5.1 sources to DLP2. Anyone?

  16. Isn’t the simplest and cheapest way of getting 5.1 movies and playback via an M-Audio Revolution 5.1 or 7.1 soundcard (http://www.dabs.com/productview.aspx?Quicklinx=49FS), or so? Or will this be impossible to configure. You can also get much cheaper 5.1 speaker sets that are set up to take 5 jacks as opposed to optical in (like this: http://www.ebuyer.com/UK/product/120414/). Or will this cause me mayhem in setting up? The M-Audio device claims to support DTS and Dolby Surround…?

  17. I’m getting some Logitech Z-5500 in a few weeks, but I just want to check a few things if that’s OK.
    AFAIK: The Z5500 support Dolby Digital, DTS, Dobly Pro Logic II.
    They have an Optical in and a Coaxial in.

    I’m planning to connect my Xbox to the Optical. Then take the optical from my Mac, pass it through a coax converter (from Maplin) and plug it in that way. I suppose I could get an optical splitter, but that means I would have to manually get up and switch the sources. Where with coax and optical, I can use the logitech remote to switch sources.

    Anyway…

    To cut a long story short, would I be better to use my Mac or Xbox 360 for playing DVD with “true” surround sound? (The 360 is connected to an identical screen as the Mac – so sound is the only discerning feature)

    If I went into iTunes and played any track that I had purchased, would this be upmixed to 5.1 with DPL II? Or do I have to have a special 2.0 track in order to upmix? My understanding was that ANY stereo source emitted from the Mac’s Optical was automatically upmixed to a kind of 5.1. Is this correct?

    Thanks again,

    Daniel Briggs :-)

  18. Type your comment here. Thanx, this is very enlightening. I appreciate your informing of just exactly what surround sound is like on the Mac. I will read again, but even at first reading, I think I understand the basics. Again, thanx.

  19. Please read this article http://geekwithfamily.com/2007/07/05/home-theater/howto-5-easy-steps-to-output-dolby-digital-from-quicktime-player/

    How to get a DOLBY DIGITAL signal untouched – from quicktime / Front Row playback – with Perian – trough to your DTS Decoder.

    Is this the best way to do this?
    And why the Midi configuration step?

    Thanx for a great article!!!
    Very very easy to understand – Very informative

    I hope you wwrite tech stuff for a living.

    Panda

  20. hi
    Great article, but if all you want to do is play video files through a mac and achieve 5.1, vlc is all you need (if you know how to use it) but unfortunately this doesn’t help those who have apple tv hence why i dint buy it.
    Ive tested this using the optical out into my sony home cinema amp and the multi channel decoding light came on therefore indicating that surround sound is being played. easy

  21. Pingback: AVforum.no - HD formatkrigen over? Streaming er utvilsomt fremtiden!

  22. Pingback: AVforum.no - HD formatkrigen over? Streaming er utvilsomt fremtiden!

  23. Just wanted to add this tidbit. I used Soft Encode to encode a 5.1 audio file and then imported into iTunes and converted to AAC and it plays the bitstream however I could get my hardware to pass the multy channel signal to the decoder if I record to disk the decoder renders the 6 channels fine. By all means the AAC is playing the 6 channel encoded audio with at his point no encoder. Next I will do an entire soundtrack to a movie and use iTunes to conver to AAC and then mux audio into the Apple TV video.

  24. here’s what I know, got an Apple TV, playing video and my receiver is recognizing it as Dolby Pro Logic (though it’s not) and I can use “advanced settings” for that and hear it through all speakers. Yes, that’s not true 5.1, but it does work.

  25. Hi, is there any progress on getting 5.1 out of Frontrow with Intel Mac mini and Mac OS 10.5.

    When I say progress has anything happened or been updated by Apple to make this easier.

  26. Great article, until I read this I was all set to get one as this is the only affordable way of playing my iTunes AAC files. But if it won’t play an ‘archived’ DVD collection in anything close to the original sound then it’s a deal breaker for me.

  27. I know this is a dated post, but since this search comes up pretty high for the google search terms for 5.1 ac3 and appletv i figured i’d add a comment onto the current state of affairs in this whole conundrum.

    Graham Booker and I have collaborated to make the Common Media Player framework for the AppleTV, part of this framework is an ingenious plugin that allows us to leverage apples dvd playback framework with 5.1 AC3 audio passed through to a receiver. This component has also allowed me to add 5.1 AC3 passthrough support to mplayer as well with relative ease.

    for more info:

    http://nitosoft.com/blog/
    http://www.cod3r.com/

Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>