static filterVariantsByAudioCodec_(variants, audioCodec) {
    return variants.filter((variant) => {
      if (variant.audio && variant.audio.codecs != audioCodec) {
        return false;
      }
      return true;
    });
  }
Filters variants according to the given audio codec.

@param {!Array<shaka.extern.Variant>} variants
@param {string} audioCodec
@private