My streams don't have camera feeds at all, so that's not a problem; I stream a full screen share only (except when I'm showing a camera pointed at a laptop scre

My streams don't have camera feeds at all, so that's not a problem; I stream a full screen share only (except when I'm showing a camera pointed at a laptop screen in an ffplay window, but that's rare). For v4l2, I imagine the simplest hacky way to do it would be to change the camera settings to result in a pure black or otherwise unusable image (e.g. zero exposure, zero brightness). That can be done with v4l2-ctl. But at that point you're probably using OBS for streaming anyway, so you might as well just use the OBS-websocket API to hide or censor the camera frame instead (and mute the audio that way while you're at it).