SelectMediaDeviceCallback

This callback is invoked when the web page asks which media input device should be used.

If there is no media input devices of the requested type (e.g. there are no video input devices), then the callback will not be invoked).

Important: the engine will be blocked until you return control from the callback.

If the callback throws an exception or the selected media device in response is not the one from the list, the system default media input device will be used.