Q: I have a Macbook Pro, and I need to send video and audio out. It has a Mini DisplayPort, so I will use that for the video, but does that also carry audio or do I need a separate audio connection?
A: The Mini DisplayPort spec does support audio and video transmission. However, audio is not implemented on all Macbook Pro models. In general, Macbook Pros made prior to mid 2010 do not carry audio on their Mini DisplayPort connection.
Further information is available here, along with instructions on identifying the exact Macbook Pro you possess.