The AAC Format
The AAC format is a standard lossy compression scheme considered by many in the technical community to be a superior successor to the MP3 format. File extensions used for this format include .m4a, .mp4, .aac and .3gp, although each of these may use media containers to encapsulate the AAC encoded audio. AAC is the audio encoding format used by the ITunes Music Store and the default format for all Apple audio devices, such as the IPod. For more information, visit the AAC wiki page.