The MPEG Alliance has finalized its newest audio specification for MPEG-4 - high-efficiency AAC (Advanced Audio Coding).

Coding Technologies developed the specification, which is also known as aacPlus. It still needs to be approved by the International Standards Organization. The new spec is both backward- and forward-compatible with AAC content and decoders.

In tests by the MPEG Alliance and the European Broadcasting Union AAC outperformed other audio codecs on quality. The solution combines technologies from MPEG Alliance with Coding Technologies' Spectral Band Replication (SBR) technology. SBRis a bandwidth-extension technique that lets audio codecs deliver the same quality at half the bit rate. It is capable of delivering streaming and downloadable 5:1 multi-channel audio at 128Kbps or CD-quality stereo at 48Kbps. It can scale down to 20Kbps.

"This level of efficiency fundamentally enables new applications in the markets of mobile and digital broadcast. aacPlus is on track to become a core component of MPEG-4 audio," Coding Technologies claims.

Libraries and reference-source code for MPEG-4 aacPlus encoders and decoders are available now for developers on OS X, Win32 and Linux.

Coding Technologies was founded in 1997 in Stockholm. It later merged with a spin-off of the Fraunhofer Institute, the inventor of MP3.