Is anot a very popular media container format designed for mobile phones; works with standard CDMA2000. The main difference from other media containers, 3GP, is the lack of support for AAC format audio tracks.
this is a lossless-format (and encoding algorithm) for Apple platforms. M4A is widely used in iPod players and as a component in QuickTime media-players. The m4a codecs decoder is found in open sources - this allows third party users to open files in that format.