how to get airplay in older mac

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AirPort Mirroring is only compatible with Early 2011 and later MacBooks Pro, and unfortunately, you can't change that, even if you are running Mountain Lion.

However, you can use a third-party app in order to mirror your computer into your Apple TV. One reliable application is AirParrot > http://www.airparrot.com

It appears no. See https://cultofmac.vanillaforums.com/discussion/35827/the-real-reason-why-macs-be fore-2011-cant-use-airplay-mirroring-in-mountain-lion-feature-cult-o

Allan