November 22, 2010, 11:20 AM — With the Monday release of iOS 4.2 and the Apple TV 4.1 software update, this officially marks the beginning of the AirPlay era. Here's a closer look at what Apple's new AirPlay media-streaming technology does and how it works.
AirPlay is an evolution of AirTunes, the system that allowed Macs or PCs running iTunes to play audio through either an AirPort Express or an Apple TV. While that functionality still exists (and will be extended to third-party devices), AirPlay expands it to allow the remote playback of video on the second-generation Apple TV.
Two different sorts of devices can send audio or video to an Apple TV via AirPlay. Macs or PCs running iTunes 10 will display the AirPlay icon (which looks like a rectangle with a triangle pointing up into it) if there's an AirPlay-compatible device on the local network. I was able to stream audio and video to an Apple TV from a Mac running iTunes 10 without any trouble.
Any iOS device running iOS 4.2 can also send audio or video via AirPlay. To enable AirPlay, you first must select the media you wish to play back, and start it playing. Then tap on the AirPlay icon and select an AirPlay-compatible device. (Devices capable of only streaming audio are signified with a speaker icon; those that can do video, with the picture of a TV set.) After a pause of about two seconds, the video you were watching on your iPad (or iPhone or iPod touch) will appear on the HDTV attached to your Apple TV.
The most remarkable thing about streaming HD video from an iPad to an HDTV wasn't the act of playback, but what happened next: I pressed the iPad's home button and switched over to the Mail app while the video happily kept on playing. That's because AirPlay works in the background, continuing to stream media remotely while you do other stuff. Want to write a movie review on your iPad while you're streaming that movie to your Apple TV? Not a problem. You can even put the iOS device to sleep and toss it in the corner; so long as it's got battery power and a network connection, it'll keep streaming.
You can control AirPlay playback from the iOS device, of course--the standard set of play and pause control buttons are available. But once the streaming starts, you can also just pick up the Apple TV's remote and control things that way. Once an AirPlay stream is going, it's really no different from watching a movie on the Apple TV directly. All the standard Apple TV remote commands work, so you can play, pause, fast-forward, and even bring up a chapter list and skip forward. The Apple TV buffers as much of the streamed file as it can, so fast-forwarding is smooth.