Maximum resolution for livestream through RTMP and webcam mode

While livestreaming through RTMP, the maximum resolution I can select is 1280p in the application. However, it is 4k for Facebook and YouTube livestreaming. Also, the webcam mode gives a maximum resolution of 1920x1080 only. Is there a way to get atleast 4k resolution either through the webcam mode or through an RTMP server? My final goal is to manipulate the high resolution stream through ROS.