Send any audio from your Mac, all around your house!
With Airfoil, you can send any audio from your Mac to AirPlay devices like the AirPort Express and Apple TV, other computers on your network and even your iPhone, iPod Touch, and iPad. Your audio plays everywhere, all in sync. Airfoil also includes:

Airfoil Speakers:  Receive and control audio from another computer.

Airfoil Video Player:  Watch video locally, with remote audio, in sync.
Airfoil in Action
Go Beyond iTunes
Why settle for just  iTunes? Select your browser and stream sites like Pandora or Last.fm. Or select other music apps like Rdio or Spotify. Stream any audio!
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Turn other devices into speakers!
With Airfoil Speakers, you can turn other computers (running Mac OS X, Windows, and even Linux) into remote outputs. And with Airfoil Speakers Touch for iOS, you can turn your iPhones, iPods Touch, and iPads into remote speakers, too.
Use with Airfoil and Audio Hijack Pro
Local Video, Remote Audio
Watch DVDs, local video files and now, web videos from sites like Hulu and Netflix, with Airfoil Video Player. Watch video on your computer, with remote audio in sync.
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Noise will be overlaid on audio playback after 10 minutes.