Add some kind of support for streaming ultrawide (21:9, 32:9) resolutions

I think this is going to be a relatively growing pain as more people are going to get 21:9 or 32:9 monitors. I like to play my games in the full resolution of my monitor (32:9), however when I stream them, the view is squashed to hell and anyone watching can barely see anything, especially if the stream is 720p.

Please add some rudimentary viewport selection setting so I can at least select the center 16:9 part of my screen to stream. Alternatively add full support for these aspect ratios and stream the entire screen properly, if a native 21:9 or 32:9 aspect ratio is detected.