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  • Company: Fraunhofer
  • Microsoft Audio ID: 0x0055
  • QuickTime FOURCCs: CBR: ('m', 's', 0x00, 0x55); VBR: '.mp3'
  • Patents

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.



mp3PRO is MP3 + SBR (Spectral Band Replication). (Standard MP3 decoders can decode mp3PRO encoded files/streams but without SBR you do not get the full quality. A SBR decoder could be share code with an HE-AAC (aacPlus) decoder as HE-AAC also uses SBR).

A US Patent application explains how to identify and locate the SBR data.


mp3HD is MP3-based lossless audio codec. This codec has backward compatibility to MP3 and extensions are in ID3 tag.

XING and VBRI headers

GAIN (MP3Gain) header

There is two versions of this header: one for MP3 and one for AAC.