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TICKET ARCHIVE -> Mp4 And Multichannel

jbbevan - Oct 14, 2005 - 10:24 am

I have MPEG-4 files encrypted on a PC in Nero Digital. They have 5.1 channel (AAC) soundtracks. My problem is recovering the soundtrack. Quicktime 7 plays the files just fine. VLC also plays the files without a problem.
But neither of them output 5.1 channels.

I have followed the MultiChannel Instructions in VLC but the 5.1 option for audio output never appears (greyed out in the preferences area).

If I do "Get Info" on the MP4 files themselves, it shows 6 channels of sound available.

I have three Macs: iMac G5, iBook G4, and Mac Mini G4. The G4's do not have "digital optical interface" so I am using an M-Audio Transit (USB to TosLink) for that purpose. The Transit works well for outputting AC-3 from DVD Player and all two channel sound.

So what it amounts to is that I can "see" the six channels (of AAC sound) in "Get Info" and other places. BUT I can't "hear" that audio.

I don't know whether I have a setup problem, a missing codec, or what(?).

Any tips would be much appreciated.

Jim

a2daj - Oct 14, 2005 - 9:49 pm

Hi Jim,

Have you ran the Apple MIDI Setup application before? If not, you may need to run that before 5.1 sound works. You'll need to select your output device form the Properties For drop down menu and then click Configure Speakers. In the sheet that appears, click Multichannel and select 5.1 Surround and then Done. You may want to click Apply first just to be sure the setting sticks. You can close the app now.

I have an M-Audio Revolution 7.1 and just tried the new HD Harry Potter trailers which use AAC 5.1 and I get multichannel audio in both Quicktime and VLC, but VLC plays some audio in the wrong channels using both CoreAudio and the HAL AudioUnit output option.

jbbevan - Oct 15, 2005 - 8:05 am

Yes, I have tried this. When I click Configure Speakers where I can choose MultiChannel, all of the multi-channel options are greyed out. The only one I can select is Stereo.

On the main Audio MIDI setup screen I click Audio Devices at the top. On the left "Properties for:" is set to M-Audio Transit USB. On the right, both Default Output and System Output are set to M-Audio Transit USB as well.

In the lower right area, Audio Output, the right drop down is set to "2 ch 16 bit." When I select "Encoded Digital Audio" the Default Output and System Outputs (above) revert to "Built in Audio" and the M-Audio Transit cannot be selected.

Thanks for your suggestion. If you have any further ideas, I'd appreciate hearing from you again.

a2daj - Oct 15, 2005 - 2:37 pm

Ah, I think I have an idea what the problem is. I misread which device you have. You have a Transmit and I read that as a Theater. The Transmit only supports 5.1 via AC-3. I don't think it can handle discrete multichannel sound like the M-Audio Sonica Theater or the Revolution PCI cards can. So it's a matter of the hardware not supporting AAC 5.1. Unfortunately, it sounds like everything is working as expected

jbbevan - Oct 15, 2005 - 5:03 pm

Ah Hah !! Now we're getting somewhere -- I guess. Since the Transit was bought specifically for this purpose I'm sorry I'll have to trash it (after three weeks of use), but I guess that's the price of moving forward.

A couple of questions: If I get Sonica Theater USB will the 5.1 channels still pass to my surround receiver as a single optical digital stream (which will then be decoded as if it were AC-3) or does it come out as six discreet analogue channels which then need to be "piped" into six analogue inputs as discreet channels?

If I'm going to ante up for yet another device I'd like to have some idea "whether" it will work and "how" it will when it works.

Thanks, I've been after this answer for about three weeks and your the first person who has really gotten to the root cause of my difficulty.

Regards,
Jim

a2daj - Oct 15, 2005 - 10:06 pm

The Sonica Theater is similar to the Transit in that it can pass through AC-3 via the digital output. However, it also supports the ability to handle discrete multichannel analog output if the proper speakers are connected directly to the Theater. With DVD playback using DVD Player you can only get 5.1 if you use the digital output since the Theater itself cannot decode 5.1 encoded sound streams used on DVDs. Apple doesn't have any built-in software decoder in DVD Player to output to the analog channels.

As for AAC 5.1 support with the Theater, I'm not sure if it would be passed through the digital output properly so that some external decode could handle it. You probably have to use the analog outputs. So I'm not sure how much of an improvement this will be to your situation.

Here's a review of the Theater.
http://www.insidemacgames.com/reviews/view.php?ID=422

Note that drivers were an issue according to the review but new drivers have been released since the review was written.

If you're curious about my setup, as I mentioned before I use a Revolution 7.1 PCI card, also made by M-Audio. It supports digital out and up to 7.1 analog channels. I have the card hooked up to a Logitech Z-680 5.1 speaker setup using both digital and analog connections. For DVD playback, I use DVD Player and switch to the digital output and let the Z-680's included decoder do its job. For most everything else I use the analog setup. For games, the analog connections are the only way to get 5.1 audio since Macs don't have any type of built-in on-the-fly 5.1 encoder either in hardware or software. For various transcoded multimedia files, I use VLC. It has a software decoder for 5.1 sound for those DIVX files with AC-3 audio tracks. It can work with DVDs too, but the app itself seems less stable with DVDs and uses more CPU. For files with 5.1 AAC sound, I use Quicktime player. But the only files I have with 5.1 AAC sound are Apple's HD trailers.

I hope that answers some of your questions. If you have more, feel free to ask.

A.J.

jbbevan - Oct 17, 2005 - 4:54 pm

A.J.
Thanks for all your help and tips. I can't use the revolution because none of my Macs have a place for additional PCI cards. But I can use the Sonica Theater USB. That model will pass AC-3 (optically) as well as provide 7 discrete audio channels.
I am hoping that since both VLC and Quicktime show the presence of these channels in these MP4 conversions they will be recoverable by the Sonica and output properly.
Your Logitech setup is a powered speaker group. I will be outputing the multi-channels to the input of a surround amplifier with six discrete analog inputs. These are the same inputs used for SACD or DVD-Audio. I'm sure it will work out fine IF the Sonica recovers the channels from the MP4s properly
As mentioned in my original message, the files were made on my PC using Nero Recode. This is the only way I know of to get MP4 with embedded AAC multi-channel. In Europe they call it Nero Digital and there are DVD/MP4 players that will play CDs burned with that technology. However, I'm not going there. I'm leaving the files on a server and projecting the files directly off of a Mac Mini. It's working very sweetly except for the final conquering of the multi-channel question.
I think you've given me the answers I need. The ball is now in my court to move forward with testing the Sonica device. Wish me luck.

Thanks,
Jim

a2daj - Oct 17, 2005 - 6:49 pm

I hope everything works and I'm really curious how things turn out. I'm going to go ahead and close this thread but feel free to respond to it again with a progress report

A.J.