handleCaptionsLoaded(target) {
    const
      textTracks = this.node.textTracks,
      playerTrack = this.getTrackById(target.getAttribute('id'));

    // Set default cue line
    if (Number.isInteger(this.options.defaultTrackLine)) {
      for (let i = 0; i < textTracks.length; i++) {
        if (target.getAttribute('srclang') === textTracks[i].language
          && target.getAttribute('kind') === textTracks[i].kind) {
          const cues = textTracks[i].cues;
          for (let c = 0; c < cues.length; c++) {
            if (cues[c].line === 'auto' || cues[c].line === undefined ||  cues[c].line === null) {
              cues[c].line = this.options.defaultTrackLine;
            }
          }
          break;
        }
      }
    }

    // set state & active player button
    playerTrack.isLoaded = true;
    this.enableTrackButton(playerTrack);
    this.checkAllCaptionsLoadedOrError();
  }
Load handler for captions and subtitles. Change cue lines if set to auto.
@param {Element} target Video track element