Will a Roku stick allow me to expand a Google TV screen? Will it control all elements and settings of the TV?
No, no Roku player will have any functionality of changing screen settings. Your only control is selecting the screen resolution, most likely just 720p and 1080p. But this won't alter the image geometry, so older content that isn't widescreen will still have black bars on the left and right, and widescreen content that is wider than 16x9 will have black bars on the top and bottom.
And honestly, you don't want to alter the image to fill the screen and remove the black bars. That's because filling the screen will do one of two things. It will either cut off some of the image (so you don't see everything the director intended), or it will distort the image, squishing the image in one or both directions. And that just looks really bad when that happens.
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