forcedSubtitlesOnly
An association between a subtitle track containing forced and nonforced subtitles and one with a subtitle track containing only forced subtitles.
Declaration
static let forcedSubtitlesOnly: AVAssetTrack.AssociationTypeDiscussion
Nonforced subtitles typically transcribe dialogue in a media asset and are typically not presented by default. Forced subtitles are those that are essential for presentation even if the user disables playback of normal subtitles (for example, when a character speaks in a language foreign to that of the audio track).
Subtitle tracks must present forced subtitles with the same content and the same language, but may have different timing.