It was designed to be the successor of the MP3 format and generally achieves higher sound quality than MP3 at the same bit rate.
It is supported on a wide range of devices and software such as PlayStation Vita, Wii, digital audio players like Sony Walkman or SanDisk Clip, Android and BlackBerry devices, various in-dash car audio systems,[when?
[9][10][11] This led to the development of the modified discrete cosine transform (MDCT), proposed by J. P. Princen, A. W. Johnson and A.
[4] Development further advanced when Lars Liljeryd introduced a method that radically shrank the amount of information needed to store the digitized form of a song or speech.
[15] AAC was developed with the cooperation and contributions of companies including Bell Labs, Fraunhofer IIS, Dolby Laboratories, LG Electronics, NEC, Panasonic, Sony Corporation,[1] ETRI, JVC Kenwood, Philips, Microsoft, and NTT.
[27] MPEG-4 Audio Object Types are combined in four MPEG-4 Audio profiles: Main (which includes most of the MPEG-4 Audio Object Types), Scalable (AAC LC, AAC LTP, CELP, HVXC, TwinVQ, Wavetable Synthesis, TTSI), Speech (CELP, HVXC, TTSI) and Low Rate Synthesis (Wavetable Synthesis, TTSI).
This is especially true at very low bit rates where the superior stereo coding, pure MDCT, and better transform window sizes leave MP3 unable to compete.
[42] AAC is a wideband audio coding algorithm that exploits two primary coding strategies to dramatically reduce the amount of data needed to represent high-quality digital audio: The actual encoding process consists of the following steps: The MPEG-4 audio standard does not define a single or small set of highly efficient compression schemes but rather a complex toolbox to perform a wide range of operations from low bit rate speech coding to high-quality audio coding and music synthesis.
Depending on the complexity of the bitstream to be encoded, the desired performance and the acceptable output, implementers may create profiles to define which of a specific set of tools they want to use for a particular application.
[27] Here is a list of some audio profiles defined in the MPEG-4 standard:[35][45] One of many improvements in MPEG-4 Audio is an Object Type called Long Term Prediction (LTP), which is an improvement of the Main profile using a forward predictor with lower computational complexity.
[47][48][49] AAC-ELD is recommended by GSMA as super-wideband voice codec in the IMS Profile for High Definition Video Conference (HDVC) Service.
The Fedora Project, a community backed by Red Hat, has imported the "Third-Party Modified Version of the Fraunhofer FDK AAC Codec Library for Android" to its repositories on September 25, 2018,[55] and has enabled FFmpeg's native AAC encoder and decoder for its ffmpeg-free package on January 31, 2023.
[56] The AAC patent holders include Bell Labs, Dolby, ETRI, Fraunhofer, JVC Kenwood, LG Electronics, Microsoft, NEC, NTT (and its subsidiary NTT Docomo), Panasonic, Philips, and Sony Corporation.
[57] Some extensions have been added to the first AAC standard (defined in MPEG-2 Part 7 in 1997): In addition to the MP4, 3GP and other container formats based on ISO base media file format for file storage, AAC audio data was first packaged in a file for the MPEG-2 standard using Audio Data Interchange Format (ADIF),[62] consisting of a single header followed by the raw AAC audio data blocks.
This format is what was defined for use in DVB transport streams when encoders use either SBR or parametric stereo AAC extensions.
This format is also referred to as a Low Overhead Audio Transport Multiplex (LATM), which is just an interleaved multiple stream version of a LOAS.
[62] In December 2003, Japan started broadcasting terrestrial DTV ISDB-T standard that implements MPEG-2 video and MPEG-2 AAC audio.
In December 2007, Brazil started broadcasting terrestrial DTV standard called International ISDB-Tb that implements video coding H.264/AVC with audio AAC-LC on main program (single or multi) and video H.264/AVC with audio HE-AACv2 in the 1seg mobile sub-program.
In later years, Apple began offering music videos and movies, which also use AAC for audio encoding.
On May 29, 2007, Apple began selling songs and music videos from participating record labels at higher bitrate (256 kbit/s cVBR) and free of DRM, a format dubbed "iTunes Plus" .
These files mostly adhere to the AAC standard and are playable on many non-Apple products but they do include custom iTunes information such as album artwork and a purchase receipt, so as to identify the customer in case the file is leaked out onto peer-to-peer networks.
It is possible, however, to remove these custom tags to restore interoperability with players that conform strictly to the AAC specification.
For a number of years, many mobile phones from manufacturers such as Nokia, Motorola, Samsung, Sony Ericsson, BenQ-Siemens and Philips have supported AAC playback.
[76] FAAD2 supports audio object types LC, Main, LTP, SBR and PS.
The native AAC encoder created in FFmpeg's libavcodec, and forked with Libav, was considered experimental and poor.
A significant amount of work was done for the 3.0 release of FFmpeg (February 2016) to make its version usable and competitive with the rest of the AAC encoders.