Allow same track to be sent N times

In rtcpeerconnection.py:

    def __assertTrackHasNoSender(self, track: MediaStreamTrack) -> None:
        for sender in self.getSenders():
            if sender.track == track:
                raise InvalidAccessError("Track already has a sender")

May I know why this constraint? is it artificial? Nothing in the spec prevents a PC from sending the same track N times in different transceivers (may be with different encoding settings).

[ibc]

I’ve looked a bit at the code. Unfortunately zero expertise with Python here. Anyway:

It comes to my mind that when the "media-player" thread in PlayerStreamTrack (src/contrib/media.py) adds frames to self._queue, and then PlayerStreamTrack.recv() gets a frame, instead of returning such a frame it could emit a “frame” event. This way, multiple “track representations” (or whatever) could get frames from the source.

Does it sound super crazy?

[ibc]

Users may still implement such a recv method as today. However aiortc would call track.recv() and “emit” each frame so N media sinks would receive such a “frame” event. Yeah, I understand it’s not as easy as that 😃