AVI
Also known as: .avi file, Audio Video Interleave, how to open avi
AVI (Audio Video Interleave) is a legacy Microsoft video container from the 1990s. It can hold many different codecs, but it lacks modern features and tends to produce larger files than MP4, so it is mostly seen in older video.
- Legacy Microsoft video container (1990s)
- Holds many codecs; format itself is dated
- Often larger than an equivalent MP4
A container, not a codec
AVI is a container format: it wraps a video stream and an audio stream into one .avi file but does not define how they are compressed. The actual compression comes from the codec inside — older AVIs often use DivX, Xvid, or even uncompressed video, which is why two AVI files can look and weigh very differently.
Because it predates modern containers, AVI has weak support for things like subtitles, chapters, and efficient streaming. Playback is best with a flexible player such as VLC, which bundles the codecs many AVI files need.
The storage angle
AVI files are frequently large, both because the format adds overhead and because the codecs commonly stored in them are less efficient than today’s H.264 or HEVC. Converting an old AVI to MP4 usually shrinks it noticeably with little visible quality loss.
If you are holding onto AVI clips from old cameras or downloads, transcoding them to MP4 (or compressing them) is a practical way to reclaim space while keeping the footage.