I connected my new Apple TV 2 to an LCD projector (Epson 9300) using a Belkin HDMI-to-DVI cable. The projector supports a variety of resolutions, but the aspect ratio is fixed at 4:3. The picture is therefore stretched vertically. How can I change the aspect ratio on the Apple TV?
How can I change the aspect ratio on the Apple TV?
You can't. The TV device plays content at the encoded aspect ratio. It is up to your viewing device to alter the display aspect if it can. Your primary options are to use a different viewing device capable of multiple aspect ratios, scaling, and/or zoom effects or you could simply letterbox your content when you encode it.
The Apple TV is designed to be used with an HDTV, all of which use an aspect ratio of 16:9, if your projector cannot support this then there is not a lot you can do.