handleBasicNorthAmericanChar(b1, b2) {
    this.curBuf_.addChar(
        shaka.cea.Cea608Memory.CharSet.BASIC_NORTH_AMERICAN, b1);
    this.curBuf_.addChar(
        shaka.cea.Cea608Memory.CharSet.BASIC_NORTH_AMERICAN, b2);
  }
Handles a Basic North American byte pair.
@param {number} b1 Byte 1.
@param {number} b2 Byte 2.