Ivan Iankovskyi

Support encapsulation of WebVTT in ISO-BMFF Spec: ISO/IEC14496-30 https://github.com/Dash-Industry-Forum/dash.js/blob/development/src/streaming/text/TextSourceBuffer.js#L342 Test Stream: https://storage.googleapis.com/shaka-demo-assets/sintel-mp4-wvtt/dash.mpd