Web/API/MediaStream/onaddtrack

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 addtrack event does not get fired when JavaScript code explicitly adds tracks to the stream (by calling addTrack()).

Syntax

MediaStream.onaddtrack = eventHandler;

Value

This should be set to a function which you provide that accepts as input a MediaStreamTrackEvent object representing the addtrack event which has occurred. The MediaStreamTrack representing the track which was added is specified in the event's track property.

Example

This example adds a listener which, when a new track is added to the stream, appends a new item to a list of tracks; the new item shows the track's kind ("audio" or "video") and label.

stream.onaddtrack = function(event) {
  let trackList = document.getElementById("tracks");
  let label = document.createElement("li");

  label.innerHTML = event.track.kind + ": " + event.track.label;
  trackList.appendChild(label);
};

Specifications

Specification	Status	Comment
Media Capture and StreamsThe definition of 'MediaStream.onaddtrack' in that specification.	Candidate Recommendation	Initial specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`onaddtrack`	Chrome Full support 26	Edge Full support 12	Firefox Full support 50	IE No support No	Opera No support No	Safari Full support Yes	WebView Android Full support 37	Chrome Android Full support 26	Firefox Android Full support 50	Opera Android No support No	Safari iOS Full support Yes	Samsung Internet Android Full support 1.5

Legend

Full support: Full support
No support: No support