The read-only property MediaStreamTrack.readyState returns an enumerated value giving the status of the track.
The MediaStreamTrack.stop() method stops playing the source associated with the track. Both the source and the track are deassociated. The track state is set to ended.
The clone() method of the MediaStream interface creates a duplicate of the MediaStream. This new MediaStream object has a new unique id and contains clones of every MediaStreamTrack contained by the MediaStream on which clone() was called.