.AVI

Introduction

AVI is the video container Microsoft introduced with Video for Windows in 1992. It interleaves video and audio in one file so they can be read from disk together. AVI was the standard video file on Windows for many years and is still common for older video, capture devices and uncompressed footage.

The original format is limited to files of about 1 GB to 4 GB. The OpenDML extension, sometimes called AVI 2.0, adds further RIFF sections and a two-level index so files can be much larger.

Structure

An AVI file is a RIFF file with the form type AVI (with a trailing space). RIFF chunks are a four-letter ID, a 32-bit little-endian size and the data, padded to an even length. LIST chunks group other chunks under a type of their own.

The hdrl list comes first. It holds the main header avih, with the frame rate, frame size and number of streams, and one strl list per stream, each with a stream header strh and a format strf that names the codec. The movi list holds the data chunks, whose IDs give the stream number and the kind of data: 00dc is compressed video for stream 0, and 01wb is audio for stream 1. The idx1 chunk at the end indexes every data chunk for seeking.

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