A lossy, size-compressed audio codec and its reference audio codec implementation. AAC files usually have M4A extension, with variants such as M4P (protected) and M4R (ringtones). Usually gives better quality for the same bit rate than the older MP3 format. Is default audio format for iTunes®, iPod® and iPhone®, and Sony PlayStation 3. Compressed formats (like MP3 and AAC) are used on portable music players.