Creating and Playing 5.1 Surround Audio via Optical Audio Out and QuickTime

FCP X supports 5.1 surround mixing, but unfortunately, there’s no way to monitor or play surround out of your Mac over the optical audio port (yes, your Mac probably has one; you may need this Toslink to Mini cable) without first encoding it to Dolby Digital. You can send multichannel audio over your HDMI port if your Mac has one (and some HDMI Thunderbolt/DisplayPort adapters), but this won’t help you if you need to connect to your audio device over optical, as many theatre audio systems require. Using Compressor and QuickTime Pro, this is fairly easy to do.

QuickTime Pro has been discontinued and will likely stop working in future versions of the OS. You can still download it here, but you’ll need a FCP 7 install on your computer or a QuickTime Pro serial number to make it work. As of Mac OS 10.9, it still works, but in the future you may need to buy and use Digital Rebellion’s Pro Media Tools.

You’ll also need Perian installed to let QuickTime 7 read AC3 and send AC3 over the digital output. It’s also discontinued but still works for this purpose as of OS 10.9. Don’t change the audio format in the Perian System Preferences pane.

First, open Terminal and enter the following to enable QuickTime Player to send Dolby Digital through the optical audio port:

defaults write com.cod3r.a52codec attemptPassthrough 1

Quit and reopen QuickTime Player 7 if it was open.

If you aren’t working in FCP X, use Compressor and click the Add Surround Sound button to assign channels. Export using the Dolby Digital Professional preset, then continue with step 5.

1. In the project properties settings for your timeline in FCP X, select Audio Channels: Surround. Assign the channels to your audio tracks using the audio inspector.

2. Go to File > Share > Add Destination. Drag Compressor Settings into the list. Type “Dolby” in the search box, and select “Dolby Digital Professional.” You must have Compressor 4 or newer installed for this option to appear.

3. With your project/timeline selected, go to File > Share > Dolby Digital Professional and pick where to export the file.

4. Make a video-only export of your file using the Share > Master File option, or you can use an existing export. I suggest using ProRes 422 or better.

5. Open your video export in QuickTime Player 7 (not 10!). Go to Window > Show Movie Inspector. If your export already has an audio track, select it and click Delete.

6. Open your exported Dolby Digital AC3 file. Select all (command-a) and copy (command-c). Put the playhead at the first frame of the movie. Choose Edit > Add to Movie. Save.

7. Connect your Mac to a Dolby Digital-capable device using an optical audio cable. This can be a cinema audio decoder or an AV receiver. Make sure that your Mac’s sound output in System Preferences (or option-click the volume widget in the menu bar) is set to Digital. Play. Your audio device should show that it’s receiving Dolby Digital signal. If it’s receiving PCM, something went wrong and you’ll only hear stereo.

If you’re playing back a film in QuickTime Player 7 from a Mac with OS 10.9 and need to hide the menu bar, follow these instructions.

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