HTML Audio/Video DOM videoTracks Property

length: get the number of video tracks available in the video.
getTrackById(id): get VideoTrack object by id.
[index]: get VideoTrack object by index.
selectedIndex: get the index of the current VideoTrack object.

var vid = document.getElementById("myVideo");

function myFunction() {
  alert(vid.videoTracks.length);
}

Meaning

The videoTracks property returns a VideoTrackList object representing the available video tracks.

Note: The first available VideoTrack object is index 0.

audio|video.videoTracks

Type	Description
VideoTrackList Object	Returns the available video tracks for the video. length: get the number of video tracks available in the video. getTrackById(id): get VideoTrack object by id. [index]: get VideoTrack object by index. selectedIndex: get the index of the current VideoTrack object.
VideoTrack Object	Represents a video track. id: get the id of the video track. kind: get the type of the video track (can be: "alternative", "captions", "main", "sign", "subtitles", "commentary", or "" (empty string)). label: get the label of the video track. language: get the language of the video track. selected: get or set if the track is active (true\|false).