MediaStream: addtrack event

Baseline

Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2017.

The addtrack event is fired when a new MediaStreamTrack object has been added to a MediaStream.

This event is not cancelable and does not bubble.

Syntax

Use the event name in addEventListener():

addEventListener("addtrack", (event) => { })

Alternatively, assign to the event handler property of the interface:

onaddtrack = (event) => { }

Using addEventListener():

const stream = new MediaStream();

stream.addEventListener("addtrack", (event) => {
  console.log(`New ${event.track.kind} track added`);
});

Using the onaddtrack event handler property (but note that this replaces other event listeners added using onaddtrack, if any):

const stream = new MediaStream();

stream.onaddtrack = (event) => {
  console.log(`New ${event.track.kind} track added`);
};

Specification
Media Capture and Streams # event-mediastream-addtrack

This page was last modified on Oct 26, 2026 by MDN contributors.