Everything you need to know about AVI
AVI (Audio Video Interleave, .avi) is Microsoft's video container format from 1992 - one of the oldest still in use. It predates streaming, modern compression, and the web. Today AVI exists primarily as a legacy format for older Windows software and archival media collections from the early 2000s.
How it works under the hood
- RIFF-based container. AVI is built on Resource Interchange File Format - a chunk structure also used by WAV. Each AVI is a series of 'chunks' tagged with FourCC codes ('movi', 'idx1', 'hdrl').
- No streaming. AVI was designed before the internet was a delivery medium. The index sits at the END of the file, meaning players must download the entire file before seeking works correctly.
- 2GB limit (legacy). Original AVI files are capped at 2GB due to 32-bit indexes. OpenDML (AVI 2.0) lifted this to 4GB but the workaround is brittle.
- Almost any codec. AVI is codec-agnostic - it has held everything from old Cinepak to modern H.264. This flexibility is also its curse: two AVIs with the same extension may need entirely different codecs to play.
Where you'll actually use it
- Legacy Windows applications expecting AVI input
- Archival video from the 2000s era
- Video editing in older versions of VirtualDub
- Capture cards that output uncompressed/lightly-compressed AVI
How it compares to alternatives
AVI vs MP4: MP4 is smaller, streamable, and supported everywhere. AVI vs MKV: MKV is the open-source modern equivalent - chapters, multiple audio tracks, attached subtitles. MKV beats AVI on every dimension except age.
Things that will trip you up
- AVI has no native subtitle track support - subtitles must be in a separate .srt file
- Some AVIs use codecs (DivX 3, Xvid) that browsers cannot play - convert to MP4 H.264 for any web use
- Long AVIs may have broken indexes - use VirtualDub or `ffmpeg -i broken.avi -c copy fixed.avi` to rebuild
Test it yourself: VLC plays almost any AVI. Use `ffprobe sample.avi` to identify the codec. For modern workflows, transcode to MP4 immediately: `ffmpeg -i input.avi -c:v libx264 -c:a aac output.mp4`.