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If I remember correctly, the QT preset uses CABAC Entropy Encoding which is not good for the ATV. I've heard that it can really make the ATV struggle.

The ATV preset doesn't use this, making it better for the ATV.

Why wouldn't you just use the Apple TV or Universal presets?

He probably wants to use the movies on both his Mac and ATV... Even though the computer will play the files encoded with the ATV preset just fine.
 
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