The MediaStream.getTrackById() method returns a MediaStreamTrack object representing the track with the specified ID string. If there is no track with the specified ID, this method returns null.
The active read-only property of the MediaStream interface returns a Boolean value that will return to be  true if the MediaStream is active, else false.
The MediaStream.id() read-only property is a DOMString containing 36 characters denoting a unique identifier (GUID) for the object.
The MediaStream interface represents a stream of media content. A stream consists of several tracks such as video or audio tracks. Each track is specified as an instance of MediaStreamTrack.
The MediaStream.onaddtrack property is an EventHandler which specifies a function to be called when the addtrack event occurs on a MediaStream instance. This happens when a new track of any kind is added to the media stream. This event is fired when the browser adds a track to the stream (such as when a RTCPeerConnection is renegotiated or a stream being captured using HTMLMediaElement.captureStream() gets a new set of tracks because the media element being captured loaded a new source.
The MediaStream.onremovetrack property is an EventHandler which specifies a function to be called when the removetrack event occurs on a MediaStream instance. This happens when a track of any kind is removed from the media stream. This event is fired when the browser removes a track from the stream (such as when a RTCPeerConnection is renegotiated or a stream being captured using HTMLMediaElement.captureStream() gets a new set of tracks because the media element being captured loaded a new source.
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.