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AVI, an acronym for Audio Video Interleave, is a file format designed to store both audio and video data in a standard package to allow its simultaneous playback. It was introduced by Microsoft in November 1992, as part of the Video for Windows technology.
It is a special case of the Resource Interchange File Format (RIFF), which divides the file's data up into data blocks called "chunks". Each "chunk" is identified by a FourCC tag. An AVI file takes the form of a single chunk in an RIFF formatted file, which is then subdivided into two mandatory "chunks" and one optional "chunk".
The first sub-chunk is identified by the "hdrl" tag. This chunk is the file header and contains metadata about the video such as the width, height and the number of frames. The second sub-chunk is identified by the "movi" tag. This chunk contains the actual audio/visual data that makes up the AVI movie. The third optional sub-chunk is identified by the "idxl" tag and indexes the location of the data chunks within the file.
By way of the RIFF format, the audio/visual data contained in the "movi" chunk can be encoded or decoded by a software module called a codec. The codec translates between raw data and the data format inside the chunk. An AVI file may therefore carry audio/visual data inside the chunks in almost any compression scheme, including:Full Frames (Uncompressed), Intel Real Time Video, Indeo, Cinepak, Motion JPEG, Editable MPEG, VDOWave, ClearVideo / RealVideo, QPEG, MPEG-4, and others.
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