The VideoTrackList property onaddtrack is an event handler which is called when the addtrack event occurs, indicating that a new video track has been added to the media element whose video tracks the VideoTrackList represents.

The event is passed into the event handler in the form of a TrackEvent object, whose track property identifies the newly-added track.

Note: You can also add a handler for the addtrack event using addEventListener().


VideoTrackList.onaddtrack = eventHandler;


Set onaddtrack to a function that accepts as input a TrackEvent object which indicates in its track property which video track has been added to the media.

Usage notes

The addtrack event is called whenever a new track is added to the media element whose video tracks are represented by the VideoTrackList object. This happens when tracks are added to the element when the media is first attached to the element; one addtrack event will occur for each video track in the media resource.


This snippet establishes a handler for the addtrack event that calls a function, addToTrackList(), passing in the VideoTrack object representing the newly-added track. In this scenario, that function's role is to add the new track to a list of video tracks available to choose from.

document.querySelector("video").videoTracks.onaddtrack = function(event) {


HTML Standard (HTML)
# handler-tracklist-onaddtrack

Browser compatibility

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