What is AVI?
AVI (Audio Video Interleaved) is a Microsoft RIFF-based multimedia container. It can carry different audio and video codecs and was one of the defining PC video file formats of the 1990s and 2000s.
Streams and FOURCC codes
AVI files contain one or more streams. FOURCC identifiers are used throughout the format to identify chunk and stream types; video codec tags such as XVID, DIVX or MJPG became familiar to users because AVI exposed this codec/container distinction very visibly.
AVI 1.0 and OpenDML
Classic AVI was extended by OpenDML (often informally called AVI 2.0) to improve indexing and support larger/more complex files. Modern software can still read a very large body of AVI material, but AVI is usually not the preferred container for new web or streaming delivery.
What might be inside an AVI?
| AVI file | Possible content |
|---|---|
| Old CD-ROM video | Cinepak or Indeo video + PCM audio |
| 2000s download | MPEG-4 Part 2 / DivX / Xvid + MP3 |
| DV capture | DV video and PCM audio |
| Technical/archive workflow | MJPEG, FFV1 or uncompressed streams depending on software |
AVI container capabilities
AVI can contain multiple streams and OpenDML removed important early size/indexing limits, but its metadata, subtitle, HDR and modern track-relationship model is much less expressive than Matroska or ISO-family containers. AVI remains important historically because classic codec handlers are often exposed through FOURCC tags such as MJPG, XVID or DIVX.
Common confusion
Changing a file from .avi to .mp4 by renaming it does not convert the container. A proper remux or transcode is required.