How do I change video resolution and frame rate from the Camera app on iPhone?

While you have always been able to change your video capture resolution and fps through Settings, it isn't very convenient, especially when you are trying to capture a fleeting moment. iOS 14 now lets you change these settings right in the Camera app. Just go to Settings -> Camera -> Record Video and toggle on Video Format Control (and do the same for Record Slo-mo).

Once you've done this, go to record something as you normally would and you will see the controls in the top right corner. You can change the resolution by tapping the number on the left and the fps by tapping the number on the right.