Part 3 of theMPEG-2 standard (formally known asISO/IEC 13818-3, also known asMPEG-2 Audio orMPEG-2 BC) defines audio coding:
MPEG Multichannel - It enhancesMPEG-1's audio by allowing the coding of audio programs with more than twochannels, up to 5.1 multichannel. This method is backwards-compatible (also known as MPEG-2 BC[1][2][3][4]), allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation.[5]
The MPEG-2 Part 3 should not be confused with MPEG-2 Part 7: AAC a.k.a. MPEG-2 NBC (Non-Backward Compatible) - the MPEG-2Advanced Audio Coding with support for multichannel encoding (up to 48 channels).[1][2]