The lastValidByteOfBlock element shall give the local address within the block of the last byte of the last audio sample. The local address range shall be understood to range from byte 0 to byte audioDataBlockSize - 1.
Used only when non-audio data is also included within the audio data block. Use with firstValidByteOfBlock and audioBlockSize elements to describe a region of valid audio samples within the block. If lastValidByteOfBlock is present then the firstValidByteOfBlock and audioDataBlockSize elements shall be required.