MP3

• 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.

Extensions

mp3PRO

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

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

XING and VBRI headers

• See this MPlayer patch: http://lists.mplayerhq.hu/pipermail/mplayer-dev-eng/2007-March/050609.html

GAIN (MP3Gain) header

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