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 n-th text track from the object's list of text tracks- the
media.textTracks
.getTrackById()
method
Instance properties
This interface also inherits properties from its parent interface, EventTarget
.
length
Read only-
The number of tracks in the list.
Instance methods
This interface also inherits methods from its parent interface, EventTarget
.
getTrackById()
-
Returns the
TextTrack
found within theTextTrackList
whoseid
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.
js
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 addtrack
and removetrack
events are set up.
js
textTracks.onaddtrack = updateTrackCount;
textTracks.onremovetrack = updateTrackCount;
function updateTrackCount(event) {
trackCount = textTracks.length;
drawTrackCountIndicator(trackCount);
}
Specifications
Specification |
---|
HTML Standard # text-track-api |
Browser compatibility
BCD tables only load in the browser