VideoTrackList

The VideoTrackList interface is used to represent a list of the video tracks contained within a {{HTMLElement("video")}} element, with each track represented by a separate {{domxref("VideoTrack")}} object in the list.

Retrieve an instance of this object with {{domxref('HTMLMediaElement.videoTracks')}}. The individual tracks can be accessed using array syntax or functions such as {{jsxref("Array.forEach", "forEach()")}} for example.

Instance properties

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

{{domxref("VideoTrackList.length", "length")}} {{ReadOnlyInline}}
- : The number of tracks in the list.
{{domxref("VideoTrackList.selectedIndex", "selectedIndex")}} {{ReadOnlyInline}}
- : The index of the currently selected track, if any, or −1 otherwise.

Instance methods

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

{{domxref("VideoTrackList.getTrackById", "getTrackById()")}}
- : Returns the {{domxref("VideoTrack")}} found within the VideoTrackList whose {{domxref("VideoTrack.id", "id")}} matches the specified string. If no match is found, null is returned.

Events

{{domxref("VideoTrackList/addtrack_event", "addtrack")}}
- : Fired when a new video track has been added to the media element. Also available via the onaddtrack property.
{{domxref("VideoTrackList.change_event", "change")}}
- : Fired when a video track has been made active or inactive. Also available via the onchange property.
{{domxref("VideoTrackList/removetrack_event", "removetrack")}}
- : Fired when a new video 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 video tracks present on a media element, VideoTrackList lets you set event handlers on the {{domxref("VideoTrackList/addtrack_event", "addtrack")}} and {{domxref("VideoTrackList/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 media element's video track list

To get a media element's VideoTrackList, use its {{domxref("HTMLMediaElement.videoTracks", "videoTracks")}} property.

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

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

videoTracks.onaddtrack = updateTrackCount;
videoTracks.onremovetrack = updateTrackCount;

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