Adaptive resolution

Could a feature be added to adapt the Stream's resolution to the resolution of the largest available source or something similar. Sometimes I'm streaming my entire desktop, and sometimes I'm streaming a game in windowed mode that is only a portion of my monitor's resolution. It isn't fun to recall what resolution each specific game uses and type that into the video settings every time I switch between these two states, so I just leave my resolution at my monitor's base resolution and center the windowed game on the scene (resulting in some black borders).
 
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