What is the AVI file format?
.avi (Audio Video Interleave) is a multimedia container file that holds audio and video data. Introduced by Microsoft in 1992 as part of the Video for Windows initiative, it is widely recognised for storing video data and was a common choice for multimedia distribution. Its MIME type is video/x-msvideo.
File structure
The .avi format is based on the RIFF structure and divides data into strictly defined chunks. The first chunk, HDRL, is a file header containing information about the video - size, number of frames, and compression algorithm parameters. The second chunk, MOVI, contains the actual audio and video data. The third chunk, IDX1, is optional - it holds index information about the location of fragmented data within the file, enabling players to seek efficiently. A later extension known as OpenDML (AVI 2.0) introduced additional index chunk types to overcome the original 2 GB file-size limit.
Compression
.avi offers an optional compression function. However, the compression method is generally less efficient than those used in MPEG or MOV formats, and compressed files are still considerably large. The format supports a wide range of codecs - including DivX, Xvid, MJPEG, and uncompressed RGB/YUV - each identified by a FourCC code stored in the stream header. Uncompressed .avi files are large in size but offer high audio and video quality even after multiple read and write operations, and such files do not require additional codecs. Modern containers like .mkv and .mp4 have largely replaced .avi for new content, offering better compression efficiency and broader feature support.
Security & safety
RISK: MEDIUMAVI is a media container, not executable code, so a genuine AVI is safe to play - but AVI has a notable history of malware tricks. The classic scam: a "movie.avi" that's actually "movie.avi.exe", or an AVI that triggers a fake "you need this codec" download which installs malware (VLC/FFmpeg need no extra codecs - never install a 'codec' a video site demands). Crafted AVI files have also exploited old player/codec bugs, so keep your player updated and prefer VLC, which sandboxes its own decoders. Online AVI converters upload your video to a third party - use a local tool (HandBrake/FFmpeg) for private footage.
Format details
in a nutshellPrograms that open AVI files
Windows2 apps
VLC media player
Open-source Drag the AVI onto VLC - it includes the DivX/Xvid/MJPEG codecs old AVIs need, so it plays files Media Player can't. 
Media Player (Windows 11) / Films & TV
Built-in Double-click to play; works for common AVIs but may show 'no video' if the codec (e.g. Xvid) isn't installed - then use VLC. 
macOS2 apps
VLC media player
Open-source Open the AVI in VLC - QuickTime often can't play DivX/Xvid AVIs, but VLC plays them all on a Mac.
IINA
Open-source Modern native macOS player (built on mpv); double-click after setting it as default for .avi. 
Linux2 apps
VLC media player
Open-source In every distro repository; open the file or run 'vlc file.avi'. mpv is an equally good alternative. 
Android1 app
VLC for Android
Open-source Open the AVI in VLC; Android's built-in players often lack the old DivX/Xvid codecs AVIs use.
VLC for iOS
Open-source Transfer the AVI via Files/AirDrop and play in VLC - iOS does not play AVI natively. Technical details
deep spec| Container family | RIFF (Resource Interchange File Format) |
| MIME type | video/x-msvideo |
| Magic bytes | 52 49 46 46 ("RIFF") at byte offset 0; form-type "AVI " (with trailing space) at offset 8 |
| Codec identification | FourCC (four-character code) stored in the strf sub-chunk of each stream header |
| Supported codecs | Uncompressed RGB/YUV, DivX, Xvid, MJPEG, Indeo, Cinepak; H.264 via DirectShow/LAV filters |
| Max file size (classic AVI) | 2 GB, constrained by the 32-bit chunk-size field in the RIFF header |
| Max file size (OpenDML/AVI 2.0) | Effectively unlimited - odml LIST chunk uses 64-bit index offsets |
| Endianness | Little-endian (standard RIFF byte order) |
| Audio streams | Multiple simultaneous audio streams supported (e.g., multiple language tracks) |
| Subtitle support | No native embedded subtitle track; external .srt or .sub files used |
| Alpha channel | Not supported by the container specification |
| Key structural chunks | HDRL (file header list), MOVI (interleaved media data), IDX1 (optional seek index) |
| Frame rate representation | Stored as integer microseconds per frame in the avih main header chunk (dwMicroSecPerFrame) |
| Video streams | Specification allows multiple video streams; in practice, players expect a single stream |
| Interleave granularity | Audio and video data interleaved in the MOVI chunk; recommended block ≤ 1 second of playback |
| Released | 1992 (Microsoft, as part of Video for Windows) |
| Specification | learn.microsoft.com |
AVI conversions
Community Q&A
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