selectionFollower
An association between two tracks that specifies when a user selects the main track, the system should follow that selection by automatically selecting the associated track.
Declaration
static let selectionFollower: AVAssetTrack.AssociationTypeDiscussion
For example, a follower of an audio track could be a subtitle track in the same language. When the user chooses a language for audio, the subtitle language “follows” the audio language selection.