Demuxer webvtt [WebVTT subtitle]:
    Common extensions: vtt.
WebVTT demuxer AVOptions:
  -kind              <int>        .D...S... Set kind of WebVTT track (from 0 to INT_MAX) (default subtitles)
     subtitles       0            .D...S... WebVTT subtitles kind
     captions        65536        .D...S... WebVTT captions kind
     descriptions    131072       .D...S... WebVTT descriptions kind
     metadata        262144       .D...S... WebVTT metadata kind


