readByte() {
    if (!this.hasMoreData()) {
      throw new shaka.util.Error(
          shaka.util.Error.Severity.CRITICAL,
          shaka.util.Error.Category.TEXT,
          shaka.util.Error.Code.BUFFER_READ_OUT_OF_BOUNDS);
    }
    return this.packetData_[this.pos_++];
  }
Reads a byte from the packet. TODO CONSIDER RENAMING THIS TO BLOCK
@return {!shaka.cea.Cea708Service.Cea708Byte}
@throws {!shaka.util.Error}