So in theory we should be doing a "scale to fit" behavior, so I'd expect that the games that don't support 21:9 would *already* resize appropriately. So, good news, you're not making a feature request for the Steam Link client side! You're making a bug report for the Steam on Linux side.

(Well, good news for *you*, maybe less so for me...)

Anyway! If you have a game that doesn't support 21:9 and isn't resizing properly on the client side, could you either turn on the performance overlay on the client and take a screenshot (on the client side, so as to capture the overlay) once the game is on-screen, or stream a game and then save off the ~/.steam/steam/logs/streaming_log.txt from your Linux box to throw somewhere you can share it? Either will include what the capture method is, as well as what size we think we're capturing.

Your specific Linux setup would also be helpful to have -- Ubuntu, Bazzite, CachyOS, etc. -- and whether you're running XOrg or Wayland.

My sneaking suspicion is that your setup is such that we're not getting the window size appropriately and so are capturing the entire desktop (empty space and all) and thus sending the 21:9 image. This will likely show up as a capture resolution that matches your desktop, and/or a capture method that starts with "Desktop" (like "Desktop Pipewire Capture" or something similar).

I *will* note that there's one case this might NOT be a bug, but rather just a "we don't support that yet": if you're running Wayland *and* the game is Wayland-native (rather than X11 running through XWayland), right now desktop capture is the only viable path we have. So that one case will *definitely* show up as "Desktop Pipewire Capture."

*That* is being worked on for the future.

But if you are running any other setup, this is likely a bug so I'd love data in order to squash it. :)

I think this is probably expected behavior.

Game creates a fullscreen window (21:9) and renders the game view centered within that window at 16:9, with black bars on the sides.

Steam captures the 21:9 window and doesn't know the content is 16:9, and can't fit the 21:9 window on the screen, so in order to show the whole window it will scale down and add black bars on the top and bottom.

The result in this case would be the original 16:9 game scaled down with black bars all the way around.

We could potentially add an option for video presentation, it could be something like:

• Letterbox
  
• Stretch
  
• Overscan

In this case you'd want the overscan option, where we fill the entire screen with video content and anything that is outside the visible area because it doesn't match the same aspect ratio as the client just doesn't get shown. This is perfect for your use case, but has the downside that if you ever play a game that supports ultra-widescreen displays, you'll just miss anything that's outside of the 16:9 area.

Originally posted by slouken:

Game creates a fullscreen window (21:9) and renders the game view centered within that window at 16:9, with black bars on the sides.

Yeah, if the *game itself* is creating a surface that covers the whole window... not much we can do, since the game is saying "I'm rendering in a 21:9 aspect ratio."

Thanks for listening to my suggestion :D
The overscan option would be perfect! As said earlier, it would cut off content on games that do support 21:9 displays, but I don't mind changing the aspect ratio to 16:9 inside in-game settings.

To add more context, here are some pictures streaming Slay the Spire 2 on my TV:
Game set to 21:9[i.imgur.com]
Game set to 16:9[i.imgur.com]

I run a standard installation of CachyOS (Wayland) on my gaming PC.