The RTCTrackEventInit dictionary's track property specifies the MediaStreamTrack associated with the track event.
var trackEventInit = {
  receiver: rtpReceiver,
  track: mediaStreamTrack,
  streams: [videoStream],
  transceiver: rtpTransceiver
};
var track = trackEventInit.track; A MediaStreamTrack representing the track with which the event is associated. This is the track that's being added to the RTCPeerConnection.
| Specification | Status | Comment | 
|---|---|---|
| WebRTC 1.0: Real-time Communication Between Browsers The definition of 'RTCTrackEventInit.track' in that specification.  |  Candidate Recommendation | Initial specification. | 
| Desktop | ||||||
|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
| Basic support | 56 | Yes | 22 | No | 43 | ? | 
| Mobile | |||||||
|---|---|---|---|---|---|---|---|
| Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | iOS Safari | Samsung Internet | |
| Basic support | 56 | 56 | Yes | 44 | 43 | ? | 6.0 | 
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
    https://developer.mozilla.org/en-US/docs/Web/API/RTCTrackEventInit/track