Compression of Mp4

Advanced Audio Coding

Advanced Audio Coding (AAC) is a standardized, loosy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format,AAC generally achieves better sound quality than MP3 at similar bit rates

AAC has been standardized by ISO and IEC, as part of the MPEG-2 and MPEG-4 specifications. The MPEG-2 standard contains several audio coding methods, including the MP3 coding scheme. AAC is able to include 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 128kbit/s (VBR). The MPEG-2 audio tests showed that AAC meets the requirements referred to as "transparent" for the ITU at 128 kbit/s for stereo, and 320kbit/s for 5.1 audio.

AAC is also the default or standard audio format for: Apple's iPhone, iPod, iTunes, Sony's PlayStation3 and is supported by Sony's Playstation Portable, latest generation of Sony Walkman, phones from Sony Ericson, Nseries Phones and the latest S40 models from Nokia, Android based phones,Nintendo's Wii (with the Photo Channel 1.1 update installed for Wii consoles purchased before late 2007), the Nintendo DSi and the MPEG-4 video standard

'High Efficency AAC' is part of digital radio standards like DAB+ and Digital Radio Mondiale.