[Feature request]: Add a centered 1:1 windowed scaling mode (no fullscreen scaling) #554

Is your feature request related to a problem? Please describe.

On larger tablets, especially 12"+ devices, fullscreen streaming can sometimes be ergonomically uncomfortable for games that require constant eye movement across the entire display.

Current scaling modes (Fit / Fill / Stretch) always scale the stream to fill the screen area, but there is no option to render the stream at an exact requested pixel size centered on screen with black borders around it.

This would be useful for users who want to simulate a smaller virtual display (for example 11-inch content on a 12.3-inch tablet) without using external workarounds.

Describe the solution you'd like

Add an optional scaling mode such as "Center", "Windowed", or "1:1" that:

• renders the stream at the requested resolution without additional scaling
• centers the image within the display
• leaves black borders around unused screen area
• optionally could include an adjustable viewport size slider (for example 80–100%)

Describe alternatives you've considered

Current workarounds are cumbersome:

• Using Borderless Gaming or window-size hacks on the host
• Android zoom tricks on the client
• Custom resolutions combined with Fit/Fill modes (still scaled fullscreen)

A native centered windowed mode would be cleaner and much more practical.

Screenshots

No response