TextTrackList

The TextTrackList interface is used to represent a list of the text tracks defined by the <track> element, with each track represented by a separate textTrack object in the list.

Retrieve an instance of this object with the textTracks property of an HTMLMediaElement object.

For a given HTMLMediaElement object media, the individual tracks can be accessed using:

  • media.TextTracks[n], to get the nth text track from the object's list of text tracks
  • the media.textTracks.getTrackById() method
EventTarget TextTrackList

Properties

This interface also inherits properties from its parent interface, EventTarget.

length Read only

The number of tracks in the list.

Methods

This interface also inherits methods from its parent interface, EventTarget.

getTrackById()

Returns the TextTrack found within the TextTrackList whose id matches the specified string. If no match is found, null is returned.

Events

addtrack

Fired when a new text track has been added to the media element. Also available via the onaddtrack property.

change

Fired when a text track has been made active or inactive. Also available via the onchange property.

removetrack

Fired when a new text track has been removed from the media element. Also available via the onremovetrack property.

Usage notes

In addition to being able to obtain direct access to the text tracks present on a media element, TextTrackList lets you set event handlers on the addtrack and removetrack events, so that you can detect when tracks are added to or removed from the media element's stream.

Examples

Getting a video element's text track list

To get a media element's TextTrackList, use its textTracks property.

var textTracks = document.querySelector("video").textTracks;

Monitoring track count changes

In this example, we have an app that displays information about the number of channels available. To keep it up to date, handlers for the addtrack and removetrack events are set up.

textTracks.onaddtrack = updateTrackCount;
textTracks.onremovetrack = updateTrackCount;

function updateTrackCount(event) {
  trackCount = textTracks.length;
  drawTrackCountIndicator(trackCount);
}

Specifications

Specification
HTML Standard
# text-track-api

Browser compatibility

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