AudioTrackList - Web APIs 编辑

The AudioTrackList interface is used to represent a list of the audio tracks contained within a given HTML media element, with each track represented by a separate AudioTrack object in the list.

Retrieve an instance of this object with HTMLMediaElement.audioTracks. The individual tracks can be accessed using array syntax.

Properties

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

length Read only

The number of tracks in the list.

Event handlers

onaddtrack

An event handler to be called when the addtrack event is fired, indicating that a new audio track has been added to the media element.

onchange

An event handler to be called when the change event occurs. This occurs when one or more tracks have been enabled or disabled by their enabled flag being changed.

onremovetrack

An event handler to call when the removetrack event is sent, indicating that an audio track has been removed from the media element.

Methods

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

getTrackById()

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

Events

addtrack

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

change

Fired when a track has been enabled or disabled.
Also available via the onchange property.

removetrack

Fired when a new audio 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 audio tracks present on a media element, AudioTrackList 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. See onaddtrack and onremovetrack for details and examples.

Examples

Getting a media element's audio track list

To get a media element's AudioTrackList, use its audioTracks property.

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

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.

audioTracks.onaddtrack = updateTrackCount;
audioTracks.onremovetrack = updateTrackCount;

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

Specifications

Browser compatibility

BCD tables only load in the browser