AirPlay video from retina MacBook Pro to Apple TV often doesn't send audio I use my retina MacBook Pro to stream some videos from the web and play them, via AirPlay, on my Apple TV 3. Every now and then, when I switch to AirPlay, the video goes to the Apple TV, but the sound continues to come from the MacBook Pro. The only way to get it to work correctly is to restart the computer. I've tried the Sound preferences, but choosing the Apple TV there still doesn't send the sound to the device. Any thoughts on what may be happening?
This is a long-standing bug in the software with OS X Mountain Lion, that unfortunately Apple has not acknowledged or addressed. The simplest solution is to restart, but I don't like to restart my computer simply because AirPlay is broken.

Instead I do the following, which fixes the issue nearly 100% of the time, without a reboot:


Turn off AirPlay Mirroring
Open Terminal.
Type in the following commands (pressing return after each):


sudo dscacheutil -flushcache

sudo killall -HUP mDNSResponder

You should see your AirPlay icon disappear and quickly reappear in your menu bar during this process. After that, fingers crossed, all should work again. I stole this fix from the Apple Support Forums and it has worked well for me.