AirVLC lets you watch videos on your Mac and play the audio through 
AirPlay, in sync.
AirVLC uses 
VLC Media Player. No need for a sub-par video player. AirVLC merely controls the awesome video player that you already know and love. Make sure you download VLC before getting started.
Get rid of the audio delay. AirPlay causes a delay in the audio, which makes videos unwatchable. AirVLC helps to overcome that by suggesting the right delay preset. More Info »
Works great with Mountain Lion. Mountain Lion supports streaming to AirPlay speakers out of the box. AirVLC finds local speakers and sets up VLC to use them. AirVLC allows you to set the correct audio delay and makes watching videos a breeze.
Works with local files and YouTube. This means that you can watch any .avi, .mkv, .mp4 you have lying around, but it also works with YouTube links. Drag a link from your browser onto AirVLC and you're done!
