TextTrackList

The TextTrackList interface is used to represent a list of the text tracks defined for the associated video or audio element, with each track represented by a separate textTrack object in the list.

Text tracks can be added to a media element declaratively using the <track> element or programmatically using the HTMLMediaElement.addTextTrack() method.

An instance of this object can be retrieved using 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 n-th text track from the object's list of text tracks
• the media.textTracks.getTrackById() method

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

length Read only

The number of tracks in the list.

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.

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.

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.

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

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

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);
}