Short notice: Managed to create video feedback with two smartphones facing each other recording each other’s display with front camera.
Will replicate later and try to post recorded stills or video sequence. Until then: Here’s a 1984 video of video feedback experiments – of course at the time done with analog equipment.
Amazing natural-looking shapes created by chaos theoretical phenomena inherent in Q-factor > 1 feedback systems… Creation of complexity as emergent phenomena.
Wolfram of Wolfram Research / Siri / Wolfram Alpha fame talks about this in his tome A New Kind Of Science.