on
Called when this participant starts publishing a track — their camera, microphone or screen share. This is where a tile gets something to render.
Fires for the local participant too: enabling your own camera delivers the stream here.
Registering a listener replays this for every stream the participant already has, so a listener attached late still renders. That replay runs inline on the registering thread.
Parameters
stream
check RTCStream.kind to tell them apart. One participant can have several at once.