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Launch your iMovie application, then navigate to the movie you want added to Apple TV. Click on the button labeled "Share," then select "QuickTime. Select the option to compress your movie, then choose "Expert Settings" from the pop-up menu that displays. Click the "Share" button again, then enter your file preferences. Select "Movie to Apple TV" from within the export drop-down menu, then click "Save. Open the Apple iTunes application on your computer. Navigate to the iMovie file you recently saved, then click and drag the file into your Apple iTunes.

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"  You will have the option to enter a name for the file, and select a file destination. " Your iMovie will then be saved in a format compatible with Apple TV.  You can now sync the movie with Apple TV within iTunes.