I have a brand new MacBook Pro (Dec. 2012) purchased with a Moshi HDMI Adapter
The cable and TV I am using work fine with another HDMI source.
I have done everything the instructions say. The video works fine and the TV shows up in System Preferences / Audio / Output but nothing changes when I select it. The sound continues to go to the built-in speakers
MacBook Pro (15-inch, Mid 2012), OS X Mountain Lion (10.8.2), Garibaldi
that is because apple ports dont support audio only video. you will have to have a separate wire for audio from the headphone jack or usb.
I've read in a number of places that pre-2010 MBP's did not support audio, bu tthe newer ones do.
They do. I use an inexpensive Monoprice adapter - here - and get audio and video from my 15" late 2011 MBP. You should be able to do the same with yours. It may be just a faulty adapter - you can get the one from Monoprice for less than $7 and try it out.
Clinton
Apple sold me this adapter with the computer, so perhaps they will make it right. I've used another Monoprice adapter in the past with poor results - had to throw it in the trash.
Can't get audio via HDMI
