static getPercentSavings(bytes) {
    return Math.round((29.1 * Math.log10(bytes) - 100.7)) / 100;
  }
Calculate rough savings percentage based on 1000 real gifs transcoded to video
@param {number} bytes
@return {number} rough savings percentage
@see https://github.com/GoogleChrome/lighthouse/issues/4696#issuecomment-380296510 bytes