Can I use Airplay with dvd to watch dvd on my tv via AppleTV 3?

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Of course. If your Mac is compatible with AirPlay Mirroring, you can watch your DVD in your TV with the Apple TV. Read > http://support.apple.com/kb/HT5404 You just have to play the DVD on your MacBook and turn on AirPlay Mirroring.

If your Mac isn't compatible with AirPlay Mirroring, you can use a third-party app like Beamer

No you cannot Airplay Mirror using DVD Player on OS X 10.8.x. DVD Player does not support Airplay Mirroring.

Be wary of using 3rd-party apps that provide the mirroring capability because they adversely affect the Core Services of the operating system and can negatively impact all aspects of Airplay.