Q: No air play in macbook pro mid 2012

About AirPlay and Airplay Mirroring

AirPlay Mirroring requires a second-generation Apple TV or later, and is supported on the following Mac models: iMac (Mid 2011 or newer), Mac mini (Mid 2011 or newer), MacBook Air (Mid 2011 or newer), and MacBook Pro (Early 2011 or newer). For non-qualifying Macs you can try using Air Parrot.

Several Apple Articles Regarding AirPlay

Apple TV (2nd and 3rd gen)- How to use AirPlay Mirroring

How to set up and configure AirPort Express for AirPlay and iTunes

About AirPlay Mirroring in OS X Mountain Lion

iTunes 10- About playing music with AirPlay

Troubleshooting AirPlay and AirPlay Mirroring

Using AirPlay

Thanks to the $15 Beamer, AirPlay streaming is still possible on Macs  that do not support Airplay and mirroring.

Another solution is the Air Parrot.

You are running OS X Lion and AirPlay Mirroring needs OS X Mountain Lion. You have two possibilities:

1. Make a backup of your files, open App Store and purchase Mountain Lion. After upgrading to OS X Mountain Lion, you will find the AirPlay icon on the menu bar and on System Preferences > Displays.

2. Purchase AirParrot > http://www.airparrot.com

If you purchased your computer after July 26th, you can upgrade to OS X Mountain Lion for free > http://www.apple.com/osx/uptodate/

As others have mentioned you need to be running Mountain Lion (10.8.x) in order to use airplay:

The apple tv needs to be up to date as well: Apple TV (2nd or 3rd generation) with software update v5.0 or later

http://support.apple.com/kb/HT5404