Advanced Audio Coding - AAC


AAC is an audio compression scheme first standardized within MPEG in 1997. AAC was designed to provide high quality audio at lower bit-rates than previous MPEG audio compression formats. AAC was further refined through the MPEG-4 standardization process and has subsequently been enhanced with bandwidth extension technology yielding High Efficiency AAC (HE AAC), and with the addition of parametric stereo, resulting in High Efficiency AAC version 2 (HE AAC v2).

Via Licensing administers a joint patent license which provides a convenient and cost-effective way to acquire the rights to practice the essential AAC patents from a set of licensors. Often referred to as the “Unified” AAC license, the program provides coverage for the AAC technologies identified in the following diagram.

MPEG SurroundExtended HE-AAC (xHE-AAC)MPEG-4 SLS

The core of this AAC "family" is a set of backwards-compatible audio coding technologies: MPEG-4 AAC LC (Low Complexity) decoders can playback MPEG-2 AAC LC bit-streams, MPEG-4 HE AAC (High Efficiency) decoders can playback both MPEG-4 and MPEG-2 AAC LC bit-streams, etc. In this way the AAC family can support a wide variety of applications ranging from extremely low bit-rates required for music delivery over cellular phone networks, to “transparent” quality (indistinguishable from the original source material) for the most discriminating listeners. Additional AAC technologies covered by the patent license include AAC-LD (Low Delay), AAC-ELD (Enhanced Low Delay) and AAC-ELD v2 (Low Delay AAC v2 Profile) which enable high quality audio for videoconferencing or other applications where low-latency performance is critical.

Via Licensing also offers joint patent licenses for three technologies that are complimentary to AAC; the Extended HE-AAC license (xHE-AAC), the MPEG Surround license and the MPEG-4 SLS license (as used in HD-AAC).

MPEG Surround>>

For additional information about Via’s AAC patent licensing program, please see our FAQ (Frequently Asked Questions) page.

A copy of the MPEG-4 Audio standard can be purchased from the ISO online store (search for “14496-3”).
ISO Online Store>>