How do I play on monitor 1 and stream at monitor 2's native resolution?

[Cause]

My intitial idea was to just duplicate screens but that doesn't allow me to select monitor 2 as source in the game and seems to treat my monitors as one.

Another idea was to use "extend displays" but if I select monitor 2 as source in the game then the game is no longer visible on monitor 1. (obviously)

I basically want the game to treat monitor 2 as primary, and obs to use monitor 2 as source (2160p60hz) while playing on monitor 1 (1080p240hz) to test if it improves video quality.

How can I accomplish that?

Thanks.

 

[Deleted member 121471]

Resolution is only one factor in determining visual quality. Can you explain why do you want to do this setup with your monitors?

Also:

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[Cause]

Well I have a 4K TV and I wanted to stream to youtube at its native resolution but I don't want to actually play on that monitor since I don't have a wireless mouse/keyboard. Therefore I was looking for a solution that lets me play on monitor 1 and stream at the TV's native resolution with the TV as primary source... but it doesn't sound possible since it would require me to launch the game twice or something of that sort

 

[qhobbes]

Have you tried setting the TV as primary monitor in Windows Settings and having it mirror to the monitor?

 

[koala]

You cannot make a game output it's graphics in two different solutions on two different monitors. If you mirror/duplicate a monitor within Windows, Windows sets both resolutions the same. If you duplicate your "small" monitor to some "big" TV, the TV gets the same resolution as the small monitor. If you try vice versa, the mirroring will refuse if you try to duplicate to a monitor that is not capable to display a higher resolution than its native resolution.
Also the refresh rate is synchronized between monitors. Both resolution and refresh rate are synchronized to the highest both monitors have in common. That is, with monitor 1 3840x2160@60 Hz and monitor 2 1920x1080@240 Hz it will become 1920x1080@60 Hz on both if you mirror both with Windows functions.
This can then be captured by OBS at 1920x1080@60Hz.
If you want to stream with some higher resolution than 1920x1080, you have to unmirror both monitors and display your game at this higher resolution on a monitor that is capable to display the higher resolution.

If your big monitor is inconvenient to play on, you can use the fullscreen projector feature of OBS. Run your game on your big monitor with a high resolution. Use OBS to capture that big monitor. Then create a fullscreen projector by right-clicking the OBS preview->Fullscreen projector (Preview)->select the small monitor. So you get a downscaled OBS preview to your small monitor. It may be suited for gaming or not, depends on the power of your PC and the game you're playing, because this preview is not as direct as the primary monitor - probably one or two frames behind. In fast shooters, this may be the difference between win or fail. In RPGs, this is usually irrelevant.