Advanced Audio Coding

Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression. It was developed by Dolby, AT&T, Fraunhofer and Sony, originally as part of the MPEG-2 specification but later improved under MPEG-4. AAC was designed to be the successor of the MP3 format (MPEG-2 Audio Layer III) and generally achieves higher sound quality than MP3 at the same bit rate. AAC encoded audio files are typically packaged in an MP4 container most commonly using the filename extension .m4a. The basic profile of AAC (both MPEG-4 and MPEG-2) is called AAC-LC (Low Complexity). It is widely supported in the industry and has been adopted as the default or standard audio format on products including Apple's iTunes Store, Nintendo's Wii, DSi and 3DS and Sony's PlayStation 3. It is also further supported on various other devices and software such as iPhone, iPod, PlayStation Portable and Vita, PlayStation 5, Android and older cell phones, digital audio players like Sony Walkman and SanDisk Clip, media players such as VLC, Winamp and Windows Media Player, various in-dash car audio systems, and streaming services such as Spotify, Apple Music, YouTube and YouTube Music. AAC has been further extended into HE-AAC (High Efficiency, or AAC+), which improves efficiency over AAC-LC. Another variant is AAC-LD (Low Delay). AAC supports inclusion of 48 full-bandwidth (up to 96 kHz) audio channels in one stream plus 16 low frequency effects (LFE, limited to 120 Hz) channels, up to 16 "coupling" or dialog channels, and up to 16 data streams. The quality for stereo is satisfactory to modest requirements at 96 kbit/s in joint stereo mode; however, hi-fi transparency demands data rates of at least 128 kbit/s (VBR). Tests of MPEG-4 audio have shown that AAC meets the requirements referred to as "transparent" for the ITU at 128 kbit/s...