platform/video.videojs/dist/video.es.js
function textTracksToJson(tech) {

  var trackEls = tech.$$('track');

  var trackObjs = Array.prototype.map.call(trackEls, function (t) {
    return t.track;
  });
  var tracks = Array.prototype.map.call(trackEls, function (trackEl) {
    var json = trackToJson_(trackEl.track);

    if (trackEl.src) {
      json.src = trackEl.src;
    }
    return json;
  });

  return tracks.concat(Array.prototype.filter.call(tech.textTracks(), function (track) {
    return trackObjs.indexOf(track) === -1;
  }).map(trackToJson_));
}
function textTracksToJson(tech) {

  var trackEls = tech.$$('track');

  var trackObjs = Array.prototype.map.call(trackEls, function (t) {
    return t.track;
  });
  var tracks = Array.prototype.map.call(trackEls, function (trackEl) {
    var json = trackToJson_(trackEl.track);

    if (trackEl.src) {
      json.src = trackEl.src;
    }
    return json;
  });

  return tracks.concat(Array.prototype.filter.call(tech.textTracks(), function (track) {
    return trackObjs.indexOf(track) === -1;
  }).map(trackToJson_));
}
Examine a {@link Tech} and return a JSON-compatible javascript array that represents the
state of all {@link TextTrack}s currently configured. The return array is compatible with
{@link text-track-list-converter:jsonToTextTracks}.

@param {Tech} tech
The tech object to query

@return {Array}
A serializable javascript representation of the {@link Tech}s
{@link TextTrackList}.