Is a format of audio/video data, which is the most popular today. It can contain files encoded by different codecs, but they will be played in sync and create a unified image to the end user. AVI container supports function in multi-threaded mode, and allows different ratios of audio and video codecs.
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.