code: function prepareRTBRequestParams(_index, bid) {
    const mediaType = utils.deepAccess(bid, 'mediaTypes.video') ? VIDEO : DISPLAY;
    const index = !_index ? '' : `${_index + 1}`;
  
    return {
      ['callbackId' + index]: bid.bidId,
      ['aid' + index]: bid.params.aid,
      ['ad_type' + index]: mediaType,
      ['sizes' + index]: utils.parseSizesInput(bid.sizes).join()
    };
  }
docs: Parse mediaType
  @param _index {number}
  @param bid {object}
  @returns {object}