MediaStream.onaddtrack

The MediaStream.onaddtrack property is an event handler 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

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
onaddtrack
26
12
50
No
No
11
37
26
50
No
11
1.5

See also

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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/MediaStream/onaddtrack