Here are step-by-step instructions to configure video/audio output on the miniDP port:

1. Install the latest software update for your MacBook Pro or iMac.
2. Connect the HDMI cable (not included) via Moshi's Adapter to your TV or AV receiver.
3. Turn on your TV or AV receiver.
4. Open "System Preferences" on your Mac, open the "Sound" option in the "Hardware" category.
5. Click on the "Output" tab and change selection from "Internal Speakers Built-in Output" to "Built-in HDMI Output".
6. Open the "Displays" option in the "Hardware" category to select the appropriate display resolution and arrangement setting.
7. Once configured, you should be able to feed both video and audio streams to your TV or AV receiver.
 

How do I know if my Mac supports audio via Mini DisplayPort?

Your computer might have a Mini DisplayPort, but it doesn't necessarily mean that it supports audio pass-through. 

The following Mac/Apple computers support audio pass-through via Mini DisplayPort.

MacBook 13" Model 7,1 (Mid 2010)
MacBook Pro 13" Model 7,1 (Mid 2010)
MacBook Pro 15" Model 6,2 (Mid 2010)
MacBook Pro 17" Model 6,1 (Mid 2010)
MacBook Pro 13" Model 8,1 (Early 2011 / Thunderbolt)
MacBook Pro 15" Model 8,2 (Early 2011 / Thunderbolt)
MacBook Pro 17" Model 8,3 (Early 2011 / Thunderbolt)

MacBook Air 11" Model 3,1 (Late 2010)
MacBook Air 13" Model 3,2 (Late 2010)

Mac mini Model 4,1 (Mid 2010)

iMac 27" Model 10,1 (Late 2009)
iMac 27" Model 11,1 (Late 2009)
iMac 21.5" Model 11,2 (Mid 2010)
iMac 27" Model 11,3 (Mid 2010)

Mac Pro Model 5,1 (Mid 2010)

If you do not know which model Mac you have, go to About this Mac > More info and then check the Model Identifier field in Hardware Overview.