AVI (Audio Video Interleave) file format was designed by Microsoft to store multimedia data such as video movies. It can store both video and audio streams which are played simultaneously.

Data stored in AVI file can be compressed. A module which allows to compress/decompress AVI data is called codec (or compressor). Each codec is identified with so-called FOURCC (four-character code) - a 32-bit unsigned integer created by concatenating four ASCII characters. E.g. if FOURCC = "DIVX", it means that its numeric value is 0x58564944.