The read-only property MediaStreamTrack.kind returns a DOMString set to "audio" if the track is an audio track and to "video", if it is a video track. It doesn't change if the track is deassociated from its source.
The read-only property MediaStreamTrack.label returns a DOMString containing a user agent-assigned label that identifies the track source, as in "internal microphone". The string may be left empty and is empty as long as no source has been connected. When the track is deassociated from its source, the label is not changed.
The MediaStreamTrack.enabled property returns a Boolean with a value of true if the track is enabled, that is allowed to render the media source stream; or false if it is disabled, that is not rendering the media source stream but silence and blackness. If the track has been disconnected, this value can be changed but has no effect.
The MediaStreamTrack.onended event handler is used to specify a function which serves as an EventHandler to be called when the ended event occurs on the track. This event occurs when the track will no longer provide data to the stream for any reason, including the end of the media input being reached, the user revoking needed permissions, the source device being removed, or the remote peer ending a connection.
The applyConstraints() method of the MediaStreamTrack interface applies a set of constraints to the track; these constraints let the Web site or app establish ideal values and acceptable ranges of values for the constrainable properties of the track, such as frame rate, dimensions, echo cancelation, and so forth.
The getConstraints() method of the MediaStreamTrack interface returns a MediaTrackConstraints object containing the set of constraints most recently established for the track using a prior call to applyConstraints(). These constraints indicate values and ranges of values that the Web site or application has specified are acceptable for the included constrainable properties.