Hold the right Option key and it records what your camera sees; let go and that clip plays on repeat as a virtual camera that Zoom, Meet or FaceTime treat as an ordinary webcam; press right Command and it dissolves back to live. The seams are crossfaded so neither the loop’s wrap nor the cut from live is a jump, and the preview ghosts the loop over your real feed at half opacity so you can line yourself up before ending it. About 650 lines of Python on OpenCV.