I don’t really know what you’re asking.

Are you asking how to play a PC game in windowed mode? If so, googling “PC game windowed mode” yields more results than I can count (I’m not gonna provide a link because idk anything about PC gaming and what method is correct/the best).

If you’re asking about something else, then you’ll have to more specific on what you’re trying to resize. If it’s an emulator window or something, you can just resize that like any old application.

Just use the standard size that shows up when you open the game?

have you tried grabbing the window by the corner? usually keeps the aspect ratio

Pretty sure theres a better solution but I guess this would work: While using OBS, capture the game when opening it (with the right aspect ratio), its better if you have some sort of layout where you can put the window capture in. Then resize the window, same in OBS (OBS always keeps the right aspect ratio), if the window then fits in your layout you got the right aspect ratio. I hope I explained it well enough so you understand it ^^'

If it works for you it works!

But I guess I could try explaining it better: When you resize a object in OBS it always has the right aspect ratio and when you capture the game in OBS while it still has the right aspect ratio you can resize the game and then check in OBS if it got the right aspect ratio. However, you need to insert some sort of layout because OBS automatically changes the object when you resize the game.

So your basically resizing the game so it fits perfectly in your layout. Hope I explained it better this time