Q: Why would Airplay mirroring play the video, but not play audio throught the TV?

While attempting to use my Macbook Pro and Apple TV to mirror an episode of a TV show from the CBS website, I could get the video of the show, but the audio won't play back through the TV.  I've done this before with no problem, but tonight when I turned on the Apple TV (gen2), it immediately installed a ssoftware upgrade to 6.1.  After the download and install completed, I had no problem getting the video of the show to mirror on my TV, but I was not able to get the sound to play through the set.  I have previously used this technique to view past episodes of TV shows that I was unable to watch live or record on the DVR.  Any Ideas?