- Microsoft Audio ID: 0x0055
- QuickTime FOURCCs: CBR: ('m', 's', 0x00, 0x55); VBR: '.mp3'
- Patents: US5214678, US5323396, US5777992
Lossy audio coding using a time-frequency transform consisting of a 32-subband polyphase quadrature filter followed by an 18-point MDCT on blocks of 576 samples. Each coded frame is padded to a byte boundary. In addition, coded frames may be padded by 1 byte as necessary to maintain a strict CBR. This rather odd design was meant to provide backwards compatibility with the blocksize and bit rates of the existing MP2 format. Although it is less efficient than using a pure MDCT (e.g. AAC and Vorbis) MP3 has become a de facto standard since it was the first widely available format.