Many gamers are starting to upgrade their displays to ultrawide resolutions with 21:9 and even 32:9 aspect ratios. While these are amazing displays to work and game on, you will have to do a bit of tweaking to be able to stream in an ultrawide resolution.
For many platforms including Twitch, the standard resolution is 16:9. You can tweak your Main Source to still use your ultrawide resolution with Gamecaster so that you don't get a stretched image.
Go into Scene Editor and place your Main Source. By default, this will be Any Game, but this can also be the game or application you'd like to use.
Move the bottom middle pip so that you can adjust the height of your source without modifying the width:
To make sure you're not getting your image stretched or compressed, make sure that you have the right height (in pixels) for 21:9 or 32:9 resolutions. For example, if your max canvas width is the default 1920px, then 21:9 height would be 822px, and 540px for 32:9.
One more option to check is to ensure the
Keep Aspect Ratiooption is ticked for your
Take note that because your source is not taking up the entire vertical space, you have some space to fill in, which you can do with a webcam, chat, images, and more so you can maximize the empty areas.