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File Format Specification Index

Basic Description

AVIs are Microsoft's approach to storing movies. It uses the RIFF format to store information in a tree structure. Both audio and video data are encoded using the Windows' installable codecs.

Basic File Format

Basic RIFF File Layout.

RIFF: AVI
	LIST: hdrl
		avih
		LIST: strl
			strh
			strf
			strd (optional)
			strn (optional)
	LIST: movi
		LIST: rec_ chunks 1..n
			xx data chunks where is the stream number
		xx data chunks where is the stream number
	idx1

Structure of the 'avih' AVI header chunk.

Structure of the required 'strh' stream header chunk.

vids: Video Stream
- RLE
- iv32
auds: Audio Stream

Structure of the required 'strf' stream format chunk.

Structure of the optional 'strd' chunk.

Structure of the optional 'strn' stream name chunk.

ASCII name of stream. "C-style" last byte zero.

Structure of the 'rec ' chunk.

Structure of the 'idx1' header chunk.

Portability

Encoding AVIs on other platforms than MS-Windows can already be a tedious task, but trying to play/open files is next to impossible, due to the large number of codecs that could be used. It has been tried before (I've seen a DOS-Player somewhere), but once it comes to undocumented codecs ..... that's it.
But then again, why should Microsoft use a portable format?

Trademarks, Patents and Royalties

To my knowledge: none.
Note that the format of certain chunks contained in RIFFs may very well be patented. A number of video and audio codecs are based of patents. If any of the more popular codecs belong to this group is beyond my knowledge.
(please read the disclaimer)

Cross-Checking Software

This section is for programmers, who wish to cross-check their implementation with others. This is an incomplete list of programs, which are available as freeware / shareware / try-before-buy etc.
The following software is able to decode AVIs:

Microsoft ActiveMovie

The following software is able to encode AVIs

MPEG2AVI

Online Resources

AVI Overview and FAQ http://www.rahul.net/jfm/avi.html (not yet read)

Paper Resources

Disclaimer

This is not the official format documentation. Although we're doing our best to keep this information as accurate as possible, there is no way of checking all of it under all possible circumstances. We're not taking any responsibility for the results of these information or lack thereof. The 'trademarks, patents and royalties' section is here just for your convenience, and is in no way complete. Please send us a note, if you find any incorrect of missing information.