after i instiall osx mountain lion,, my mac book air do not have icon,, this is 3 yrs old macbook.. what can i do
Welcome to Apple Support Communities
AirPlay Mirroring requires a Mid 2011 or newer MacBook Air > http://support.apple.com/kb/HT5404
As your MacBook Air isn't compatible, you have to use a third-party app like Beamer or AirParrot to mirror your MacBook screen onto the Apple TV
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