Depending on the model of MacBook Pro you're working on, it may not pass audio through the Mini DisplayPort. In that case, you'd need to connect the headphone port to the audio-in port on the TV for audio.
Thanks Allen! I looked at my Model and does not support audio through the mini displayport...since my MBpro made mid 2009...I found it interesting that the link you provided "about Mini DisplayPort to HDMI adapaters" in your response that identified different Mini HDMI adapter that display both AV for my MBpro model. This adpater is Moshi mini DP to HDMI adapter with Audio support. Do you have any info about this adapter and whether it would work?