What is an AVI file?

AVI (Audio Video Interleaved) is a multimedia container format introduced by Microsoft in November 1992 as part of its Video for Windows software. AVI files contain audio and video data and metadata (such as subtitles and closed captioning) in a file container that allows synchronous audio-with-video playback. Like the DVD video format, AVI files support multiple streaming audio and video, allowing for convenient file-sharing for uses such as reference, archiving filmed material, editing and transcription. Most AVI files also use the file format extensions developed by the Matrox OpenDML group in February 1996. AVI files use the file extension .avi.

AVI is a derivative of the Resource Interchange File Format (RIFF), which divides a file’s data into blocks. Each block is identified by a FourCC tag. An AVI file takes the form of a single block in a RIFF formatted file, which is then subdivided into two mandatory blocks and one optional block.

By way of the RIFF format, the audio-visual data contained in the blocks can be encoded or decoded by an encoder/decoder. Upon creation of the file, the codec translates between raw data and the compressed data format used inside the block. An AVI file may carry audio/visual data inside the chunks in virtually any compression scheme, including Full Frame (Uncompressed), Intel Real Time (Indeo), Cinepak, Motion JPEG, Editable MPEG, WDOWave, ClearVideo/RealVideo, QPEG and MPEG-4 Video.

In addition, AVI files can embed Extensible Metadata Platform (XMP). By design, any RIFF file can legally include additional chunks of data, each identified by a four-character code. As such, it is theoretically possible to expand any RIFF file format, including AVI, to support almost any conceivable metadata.

Since its introduction in the early 90s, new computer video techniques have been introduced which the original AVI specification did not anticipate. For example, there are several competing approaches to including a timecode in AVI files, which affects usability of the format in film and television post-production, although it is widely used. Also, AVI was not intended to contain video using any compression technique which requires access to future video frame data beyond the current frame. More recent container formats (such as Matroska, Ogg and MP4) solve these problems, although software is freely available to both create and correctly replay AVI files.

DV AVI is an AVI file where the video has been compressed to conform with DV standards. There are two types of DV-AVI files. In type 1 multiplexed audio-video is saved together into the video section of the AVI file. This saves space, but Windows applications based on the VfW API do not support it. Type 2 is supported by VfW applications, although the file size is slightly larger.