MPEG-2 (aka H.222/H.262 as defined by the ITU) is a standard for the generic coding of moving pictures and ISO/IEC 13818 MPEG-2 at the ISO Store. It describes a combination of lossy video compression and lossy audio data compression methods, which permit storage and transmission of movies using currently available storage media and transmission bandwidth.
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.