(some positive integer value)
Height in px
Actual height may be less based on bandwidth allowances
Limiting the height can force the camera to use higher frame rates
Limiting the height can reduce the CPU load
https://vdo.ninja/supports will list the support resolutions of your default camera.
https://webrtchacks.github.io/WebRTC-Camera-Resolution/ Is a tool to help you find the resolutions supported by your camera
You can use &scale=50 also, as a viewer, to scale down a selected width/height to something more exact.