How to get started with AirPlay
Mac: Streaming video outside iTunes If you want to stream non-iTunes video—say, movies in formats that iTunes doesn’t support, or videos you don’t want to add to your iTunes Library—you have two options: video mirroring (see the next item) or third-party utilities. Beamer ($15) is a good option for the latter. When you launch Beamer, it asks you to choose which Apple TV to stream to; then you drop any supported video file (AVI, FLV, M4V, MKV, MOV, MP4, WMV, or VOB files) onto Beamer to begin streaming it.
In addition to letting you stream video that resides outside of iTunes, Beamer is also useful for streaming video from older Macs that officially don’t support AirPlay for video. Beamer even streams subtitles and 5.1 audio.
Mac: Mirroring the Mac’s display As with recent iOS devices, you can mirror your Mac’s entire display to your TV over AirPlay, provided you’re running OS X 10.8 Mountain Lion on a compatible Mac: a mid-2011 or newer iMac, Mac mini, or MacBook Air; or an early-2011 or newer MacBook Pro.
On any of these Macs, whenever OS X detects a compatible Apple TV on your local network, a new AirPlay menu appears in the menu bar, and an AirPlay Mirroring pop-up menu appears in the Displays pane of System Preferences. From either menu, choose your Apple TV to start mirroring; while mirroring, the icon for the systemwide AirPlay menu glows blue.
When mirroring your Mac’s display to an Apple TV, you can choose the resolution of your display‚ and, thus, of the mirrored signal sent to your TV. Choose Best For Display (in System Preferences) or This Mac (from the systemwide AirPlay menu), and your Mac’s display remains at its native resolution. This setting will make for the best appearance on your Mac, though the mirrored image may not fill your TV screen. Choose Best For AirPlay (in System Preferences) or Apple TV (from the AirPlay menu), and your Mac’s display resolution changes to a 16:9 ratio that best matches your TV’s native resolution. This is the way to go when you want to have the sharpest image on your TV.
System Preferences also offers a Scaled option, which lets you choose any non-native resolution that’s supported by your Mac’s display, though this option often results in a blurry image on both your Mac and your TV.
Don’t have a Mac that supports AirPlay mirroring? AirParrot is a $10 utility that lets you mirror an older Mac’s screen to an Apple TV. On both older and newer Macs, AirParrot also allows you to use your TV as a second display for your Mac.
Stopping the stream
Whichever type of streaming you’re doing, with whichever device, you can stop streaming by using the same AirPlay control or menu through which you originally started your streaming: Just switch the selected output or destination back to your iOS device or Mac. When mirroring a Mac’s display, just choose Turn Off AirPlay Mirroring (from the systemwide AirPlay menu) or Off (in System Preferences).
Alternatively, if you’re streaming from a particular app, quitting that app usually stops streaming. Finally, when streaming to an Apple TV, you can usually stop streaming or mirroring by pressing the Menu button on your Apple TV’s remote.
Updated 5/29/2013, 12:15pm to add mention of AirPlay-equipped home-theater receivers.