iTunes 10.x supposedly plays 5.1 surround? and how is that?

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Level 1

135 points

iTunes 10.x supposedly plays 5.1 surround? and how is that?

I have tried all manner of transcoding of commercial and homemade 5.1 surround (done with Soundtrack Pro) and not gotten a wrapper or codec combination that works with the supposedly 'new playable 5.1 surround' iTunes... I also thought I read somewhere that Airplay will wirelessly send to express/extreme units in 5.1 surround... have used .mov, .aac, etc etc and confirmed in metadata of multiple channels including some 6 channel discrete attempts...

Also tried the Chris Breen routine by setting up Audio Midi, used his code suggestions for A/52 in terminal, setup the output in Sound prefs pane, and all that other stuff...

again, kind of useless if this doesnt in fact work....

I cannot seem to send audio of any sort in playback from a stereo coded .mov I made with my own gear either...

Playing to a N- Airport Express hooked up optically to a 5.1 surround stereo system and using latest iTunes....

Also have the Mac tower connected optically to a 5.1 stereo for previewing and editing in surround

Havent managed to figure out how to stream to my network using the Streaming wizard of VLC yet, so thats only a prospect....

So I guess Airplay/iTunes 10.x doesnt actually do 5.1? nor with iTunes read and playback a 5.1 thru optical direct as opposed to wirelessly?

Mac OS X (10.5.8)

Posted on Oct 10, 2010 11:24 PM

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Answer 1

artysan

Level 1

19 points

Oct 12, 2010 3:24 PM in response to Brad Schurman

Brad,

I do not have specific knowledge of iTunes' ability to pass along two-channel encoded surround to a decoder, such as that in a surround receiver. However, I specialize in broadcast work with surround encoding so I am very familiar with the technology. Since iTunes strictly handles two channels of audio, if 5.1 claims are being made, it is playing back two-channel encoded surround. What two-channel encoded formats are you aware of that are supposed to work with iTunes? Dolby Digital? That's the most common for consumer applications.

Can you play encoded material from your Mac to a surround decoder in any other application than iTunes? Any two-channel playback app or editor should be able to do this if the recorded material is encoded with the same format as your decoder. Whether connected optical or analog makes no difference. It is just two channels, L & R as far as the hardware is concerned.

If you can make the above work, which should be no problem, the next test would be to import that same audio in WAV format into iTunes and try it again. iTunes does a great job of playing full-rez WAV stereo using the Mac's audio as well as external interfaces, so encoded material should work as well.

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Answer 2

Brad Schurman Author

Level 1

135 points

Oct 18, 2010 7:50 PM in response to artysan

All the following files failed playback through Airport Express/iTunes... not one gave any audio at all, not even the hissing ones...so the audio results below are relating to the tower's speaker and the SPDIF connected directly to the tower at the same time. I named the files according to how I transcoded them in the process.

I used a variety of apps from Compressor to MpegStream clip to Quicktime Pro 7 and ffmpegX and came up with the following varieties for testing.... I have Perian installed as a prefpane. FCP Pro Studio HD and all the fixings with that... the 6_channel is a test file i found somewhere, forgot which is the original below. (I think I milched it off an AV H. Theatre setup and test disc somewhere)

6 ChannelID(1).mov
6 ChannelID copy.m4a
6 ChannelID copy.wav
6 ChannelID.m4a
6 ChannelID.mov
6 ChannelID.wav
6 ChannelID(1).m4a

the only ones that would play in iTunes 10.x were the .mov ones (force dropped on itunes) otherwise the .mov obviously opened in QT. They DIDNT play in vlc though.

VLC could only play the wav's and the 6 ChannelID(1).m4a.

Tried again and encoded a short segment off the matrix dvd i own into the following using all the above and for yucks, all these and the mkv from handbrake for output....

THE MATRIX_16X9LB_NAMERICA Title 12 (Ch1 - Ch1).ac3
THE MATRIX_16X9LB_NAMERICA Title 12 (Ch1 - Ch1).mov
THE MATRIX_16X9LB_NAMERICA Title 12 (Ch1 - Ch1).VOB.ff.avi.ac3
THE MATRIX_16X9LB_NAMERICA Title 12 (Ch1 - Ch1).VOB.ff.avi
THE MATRIX_16X9LB_NAMERICA Title 12 (Ch1 - Ch1).VOB

the only one iTunes would open was THE MATRIX_16X9LB_NAMERICA Title 12 (Ch1 - Ch1).mov (was one of three that had audio only, no vid encoded with it), and it played with most of the soundtrack drowned out by a static-bursting hissing sound over top...
ALL of the above played fine both audio and those with video in VLC

then finally tried one last time and came up with

6channel discrete.m4v
6channel discrete.mov
ac3passthru.mkv
ac3passtrough.m4v
ac3passtrough.mov
ipod aac dolby2 mixdown.mov

ac3passtrough.m4v played with the static sound again, ac3passtrough.mov played the static but only through the tower's built in speaker, and ac3passthru.mkv didnt play in itunes at all (obviously wouldnt)

...but...

all played fine in VLC except ac3passtrough.mov which sounded all syntho pop computer industrial music wierd...

All were played through SPDIF out to AV stereo with 5.1 directly attached to tower while also streamed thru airport to airport express to ANOTHER 5.1 system using SPDIF separately, but NONE of the audio played through there regardless if audio, video, or both encoded in the files... which is what got me asking 'what gives' in the first place if it is supposed to be able to stream 5.1 now thanks to the new itunes 10.x

then i tried some Kenny Aronnoff Surround.mp3 but that only shows up as 2 channel Joint Stereo, so I guess it only works directly in surround if you use the MP3sPlayer it comes with from Fraunhofer IIS.

I didnt know about encoding surround into only 2 channels so I didnt... all the stuff inc. the wav files show up as 5.1 - 6 channels when scoping their profiles with VideoSpec. ac3passtrough.mov was the closest thing to only 2 channel as it shows up as ac3-a52 codec'd and 3 (triphonic) under its profile analysis. ipod aac dolby2 mixdown.mov shows up as 2 channel but handbrake apparently made it non surround 2 channel.

The VOB profile says AC3-A52 codec and stereo but showing the 5.1 channel designations (not just 2 stereo/ L and R like two other ac3's), so that one actually looks like it would work, but again only playing in VLC which doesnt do AirPlay/iTunes/Airport express...

all in all none of this helps me in playing thru airport, but does give me an idea what I can play just locally through the tower direct SPDIF... (not my objective here)

I did find a couple surround sound podcasts that inc. music in them for reference playback and it played through the ipod direct (L and R RCA jacks) and itunes over airport, will have to try analyzing them and finding out HOW they play it I guess

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Answer 3

artysan

Level 1

19 points

Oct 18, 2010 9:18 PM in response to Brad Schurman

Brad,
Thanks for sharing the history of your exhaustive investigation. Before addressing the Airport issue, which I now understand to be your primary one, I am curious about your last paragraph. Did the surround podcast play back in surround in that test? In other words, is whatever codec Apple is using working through the Airport radio? I would expect it could be treated as an open protocol for bit-for-bit playback.

**Please forgive the lengthy following, but you sound technically interested, and it may ultimately help you to discover the issue if properly encoded 2-ch audio is truly not passing the Airport link.

START
In professional video facilities, audio and video are embedded using the HD/SDI protocol, which - on a single coax - carries the uncompressed HD video as well as up to 4 blocks of 4 channels each, for a total of 16 channels, 48k/16bit AES-format audio signals. Most common for surround broadcast is to use only eight: 5.1 plus an optional discreet Lo/Ro, which is a separate stereo mix. These are de-embedded within the studio into 4 AES 2-ch pairs so that the signals can be treated, re-mixed as needed and then re-encoded into consumer formats for broadcast and media creation.

Dolby creates the protocols and a pair of hardware processors for the Dolby Digital consumer format, for example, which I often use to send and record a full surround program at remote locations. The processors accept all my channels -usually in AES pairs, and create a Dolby E Format data signal, suitable for terrestrial (copper, fiber) or air (radio uplink) use. The Dolby E Format contains important metadata describing my intended overall program and LFE levels, etc and a timecode signal. This unit also decodes the result on the spot for quality check monitoring as well.

Wherever this Dolby E signal arrives (network control), it carries all information necessary to reconstruct my original mix, right down to my intended levels, in reference to digital full scale. A companion processor, the Dolby Digital Encoder, takes either the entire E-stream, including audio and metadata; or if available, the original discrete audio (pre-recorded with timecode for example) WITH the Dolby E metadata and creates the 2-channel signal suitable for distribution (media or air) to consumers for playback using surround receivers, amplifiers. END

It's obvious that Apple's codec should work flawlessly with the Airport. But the Airport also works just fine with non-Apple files, such as AC3. The question then is, in what format do you need to create your own content to use the Airport as a 'playback radio' for 2-ch encoded surround.

Which brings us right back to the top question in my response to you - did the surround podcast's, via the Airport, ACTUALLY play back in surround on your system? If not, have you scrolled through all the available decoders in your particular receiver/amp? I don't know what format was used on the podcast you have. That would be nice to know.

If you DO manage to hear surround on this 2-ch signal thru the Airport, then you should be able to remove the Airport from your troubleshooting and concentrate on finding a 2-ch encoding scheme to create the audio portion of the files for your original content. Once they work hardwired into your playback system, the Airport should have no problem with them.

Hope something here helps.
Peter

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Answer 4

dknightd

Level 3

705 points

Oct 19, 2010 4:45 AM in response to Brad Schurman

iTunes will only play DTS encoded multichannel sound. And all effects have to be turned off in itunes to pass the digital signal intact.

See

http://support.apple.com/kb/TA47850?viewlocale=en_US

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Answer 5

artysan

Level 1

19 points

Oct 19, 2010 9:12 AM in response to dknightd

dknight,
Awesome, cut to the chase answer. There you have it Brad - DTS is the codec you seek.
Peter

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Answer 6

Brad Schurman Author

Level 1

135 points

Oct 19, 2010 12:36 PM in response to artysan

aw nutz... means getting a new machine and rebuying FCP Studio then, as I dont have DTS... Just the A52 (open source, came in Handbrake or other freeware install, or forgot how I got that?) and AC3 that came with FCPsHD 5.x. AC3 is alright surround, I just have to figure out how to smoothly engineer in it with a non existant GUI (Soundtrack Pro and FCP in the FCPS. 5.x kit has no multichannel pan, its all individual channel 'touch and latch control' without a single toggle to sweep all the audio to the video track... sigh). Also means the open source and freeware apps are only good to a point, and not much for transcoding or authoring/modifying existing stereo files properl.

I did set iTunes to all those 'off' presets as mentioned in the support doc as provided by dknight and it didnt change the direct-linked SPDIF hiss sounds in any of the situations...

as for the airport streaming, again no change because itunes would just not open any of the transcoded files other than the ones mentioned in the testing previously mentioned. Not sure why it wouldnt open the wav file if someone here thinks it plays wav, or the ac3

When I checked the difference between hissing/stuttering ac3passthrough files the following showed in the Info pane of itunes:

ac3passthrough mpeg-4 video file, Stereo, Dolby Digital 5.1, encoded: Handbrake (noise through onboard speaker and connected SPDIF AV stereo)
ac3passthrough Quicktime movie file, Multi, Dolby Digital 5.1, encoded: Handbrake (noise through onboard speaker only)

the one Holophone I quickly looked at says MPEG-4 video file, Low Complexity, stereo channels...

I still havent checked the 'how did it' formats and codecs of the Dolby podcasts, but for your interest theres a couple including one about Holophone (Canadian invention, 5.1 surround inc. video to give you a visual reference where the sound should be) that I have checked via old ipod through L&R RCA jack to stereo unit as well as streamed from other room through Express... seems to work, but have to hit the airport (international) in a few mins. so cant go into checking on those files...

the Kenwood AV via SPDIF direct to tower Im having doubts on now, maybe its Dolby logic is flaky or something, it has a pro logic setting then the PLII settings for enhancing mono and regular stereo signals, then the PROPERLY working AV I have has like 2 dozen surround settings from Dolby PLII + THX to regular Dolby and forced enhanced modes... fairly sure if the A.Express attached to it was doing its duty this unit would be faithfully reproducing without 'enhancing whats not there', as in faking me out with enhancing a non-surround stereo streamed file or podcast.

Thanks for helping out guys, looks like I have a no go situation other than someone elses' podcast or pre encoded 2 channel stereo file 😟

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