What is AacPlus?

The Advanced Audio Coding in MPEG-4 Part 3 was enhanced relative to what was previously specified in MPEG-2 Part 7, in order to provide better sound quality relative to the bit rate used for the encoding.

It is assumed that any Part 3 and Part 7 differences will be ironed out by the ISO standards body in the near future to avoid the possiblity of future bitstream incompatabilites. At present there are no known player or codec incompatibilities due to the newness of the standard.

AAC's mulitple codecs

* One codec defined in MPEG-4 Part 3 is known as Low Complexity Advanced Audio Coding (LC-AAC).
* Another codec is known as High-Efficiency Advanced Audio Coding (HE-AAC)
* Another codec is known as Scalable Sample Rate Advanced Audio Coding (AAC-SSR).
* Another codec is known as Bit Sliced Arithmetic Coding (BSAC)

High Efficiency AAC is a lossy data compression scheme for streaming audio. It is based on MPEG-4, and combines three techniques: Advanced Audio Coding (AAC), Spectral Band Replication (SBR), and Parametric Stereo (PS).

The aacPlus codec was standardized by the MPEG under the High Efficiency AAC (HE-AAC) name. The codec can operate at very low bitrates and is good for Internet radio streaming. It is claimed that a 48 kilobit-per-second stream will produce higher quality output than MP3 at 128 kbit/s. While listening tests[1] suggest that this claim is unfounded, aacPlus generally outperforms other popular codecs in the 32-64 kbit/s range. Its main competition for delivering acceptable quality at these bitrates comes from MP3pro, which also employs SBR.

aacPlus is supported in the free FAAD2 decoding library (and all players incorporating it), Winamp, and foobar2000. iTunes does not yet support aacPlus; the only players for Mac OS X are VLC and MPlayerOSX.