docs: function bufferedPercent(buffered, duration) {
    var bufferedDuration = 0;
    var start = void 0;
    var end = void 0;
  
    if (!duration) {
      return 0;
    }
  
    if (!buffered || !buffered.length) {
      buffered = (0, _timeRanges.createTimeRange)(0, 0);
    }
  
    for (var i = 0; i < buffered.length; i++) {
      start = buffered.start(i);
      end = buffered.end(i);
  
      // buffered end can be bigger than duration by a very small fraction
      if (end > duration) {
        end = duration;
      }
  
      bufferedDuration += end - start;
    }
  
    return bufferedDuration / duration;
  }