static getCodecBase(codecString) {
    const codecsBase = [];
    for (const codec of codecString.split(',')) {
      const parts = shaka.util.MimeUtils.getCodecParts_(codec);
      codecsBase.push(parts[0]);
    }
    return codecsBase.sort().join(',');
  }
Get the base codec from a codec string.

@param {string} codecString
@return {string}