Optional defaultOptional idOptional in_If this field is present, it means that references for this text track are available in the associated video's manifest
Optional kindkind of text track
Optional labellabel for the track
Optional mime_mime_type for the track
Optional sourcesarray of sources for .vtt files (note that in many cases there will be one source with a src value identical to the text_tracks.src value, but this array is included in case there are multiple protocols available, such as http and https)
Optional src?: stringOptional srcURL for the .vtt file
Optional srclang2-letter language code, such as "en" or "ko"
whether this is the default track