The d4p_media_tracks element is analogous to the HTML5 <track> element. It is to be used to specify external tracks that go along with the media file, such as subtitles for different languages, captions, or metadata. The @kind attribute specifies the kind of track, and possible values are subtitles, captions, descriptions, chapters, and metadata. @kind is required. The @src attribute gives the source of the track; it is required. @srclang provides the name of the language of the track; it is optional. The @label is a human readable title for the track.