TextTrackList

{{APIRef("HTML DOM")}} 

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 {{domxref("textTrack")}}  object in the list.

Text tracks can be added to a media element declaratively using the {{HTMLElement("track")}}  element or programmatically using the {{domxref('HTMLMediaElement.addTextTrack()')}}  method.

An instance of this object can be retrieved using the {{domxref('HTMLMediaElement.textTracks', 'textTracks')}}  property of an {{domxref('HTMLMediaElement')}}  object.

For a given {{domxref('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

{{InheritanceDiagram}} 

Instance properties

This interface also inherits properties from its parent interface, {{domxref("EventTarget")}} .

• {{domxref("TextTrackList.length", "length")}}  {{ReadOnlyInline}} 
  • : The number of tracks in the list.

Instance methods

This interface also inherits methods from its parent interface, {{domxref("EventTarget")}} .

• {{domxref("TextTrackList.getTrackById", "getTrackById()")}} 
  • : Returns the {{domxref("TextTrack")}}  found within the TextTrackList whose {{domxref("TextTrack.id", "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 {{domxref("TextTrackList/addtrack_event", "addtrack")}}  and {{domxref("TextTrackList/removetrack_event", "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 {{domxref("HTMLMediaElement.textTracks", "textTracks")}}  property.

const 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 {{domxref("TextTrackList/addtrack_event", "addtrack")}}  and {{domxref("TextTrackList/removetrack_event", "removetrack")}}  events are set up.

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

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

Specifications

{{Specifications}} 

Browser compatibility

{{Compat}}