WebvttHlsSourceSettings   
    Settings specific to WebVTT sources in HLS alternative rendition group. Specify the properties (renditionGroupId, renditionName or renditionLanguageCode) to identify the unique subtitle track among the alternative rendition groups present in the HLS manifest. If no unique track is found, or multiple tracks match the specified properties, the job fails. If there is only one subtitle track in the rendition group, the settings can be left empty and the default subtitle track will be chosen. If your caption source is a sidecar file, use FileSourceSettings instead of WebvttHlsSourceSettings.
Types
Properties
Optional. Specify alternative group ID
Optionally specify the language, using an ISO 639-2 or ISO 639-3 three-letter code in all capital letters. You can find a list of codes at: https://www.loc.gov/standards/iso639-2/php/code_list.php
Optional. Specify media name