Basic Description

RIFFs are capable of holding various types of data. The file extension for RIFFs is dependent on its content.
Examples are:

• ANI for animated cursors
• AVI for videos
• BND file bundles
• DXR Macromedia Director Files (notice: Network byte order!)
• PAL for color palette information
• RDI for bitmaps
• RMI for MIDI
• WAV for digital audio

Basic File Format

The price for the flexibility of holding different types of data is a file structure, that isn't easy to understand. A RIFF is - more or less - a hierarchical structure. The 'directory entries' are defined by chunks. Every chunk contains either data or a list of chunks. This document will occasionally refer to the analogy of a file system, every chunk is either a file or a subdirectory. All chunks have the same structure:

Name		Size	Description
ID		4 byte	four ASCII character identifier, padded with ASCII 32 (space) if less than 4 characters
Size		4 byte	size of Data
Data		Size bytes	the 'payload'

unused 1 byte present, if size is odd

Structure of the 'RIFF', 'RIFX', and 'LIST' chunks

The first chunk is the root entry and must have a ID of 'RIFF' or 'RIFX', the prior being the most common version. 'RIFX' specifies 'Motorola' byte order (most significant byte first), whereas 'RIFF' specifies 'Intel' byte ordering (least significant byte first). This document will stick to 'RIFF'. That first chunk contains all other chunks of the file in its Data. Its Size field will therefore always contain a value of filesize - 8.
The structure of Data is dependent on its ID. There are two directory- IDs, 'RIFF' and 'LIST'. They contain a 4-byte ASCII header, leaving the following structure:

Name		Size	Description
ID		4 byte	four ASCII character identifier
Size		4 byte	size of Data
Data		Size bytes	the 'payload'
HeaderID		4 bytes	'Name' of the list
Data Size		4 bytes	List of chunks

There will never be a final extra byte, since the Size will always be even. The HeaderID in the RIFF chunk usually matches the file's extension.

Structure of the 'JUNK' chunk

To align RIFF chunks to certain boundaries (i.e. 2048bytes for CD-ROMs) the RIFF specification includes a JUNK chunk. Its contents are to be skipped when reading. When writing RIFFs, JUNK chunks should not have odd number as Size.

Name		Size	Description
ID		4 byte	four ASCII character identifier 'JUNK'
Size		4 byte	size of Data
Data		Size bytes	nothing
unused		1 byte	present if Size is odd

The 'INFO' List

RIFF files may include a 'LIST' chunk with a HeaderID of 'INFO'. All chunks listed in this 'directory' should be pure ASCII chunks, and give various information on the file.

Name		Description
IART		artist
ICOP		copyright
INAM		name

Knowing these structures, one can implement a program that produces a hierarchical list of the file's contents. RIFFview! does this. A simple RIFF could look like this:

RIFF				first chunk, the 'root directory'
		data		some data
		JUNK		some padding to align the next chunk
		LIST		a list of chunks 'subdirectory'
			data	a 'file' in the list
			data	another 'file'
		data		another 'file' in the 'root directory'

That's all for generic RIFFs. All other chunks are part of a special file type. For an interpretation these look at the page with their corresponding file type.

Portability

RIFFs were designed with mainly one target platform in mind: MS-Windows. The existence of huge numbers of RIFF files (i.e. WAV Collections) made it necessary to read them on other platforms. The RIFX was included in the RIFF specs to for portability purposes, but many RIFF decoders are not capable of reading those files (DaubNet RIFF Viewer V1.3 now can!) , so it may be wise for RIFF encoders to stick to that byte order, even on systems with Motorola byte order.

Trademarks, Patents and Royalties

To my knowledge: none.
Note that the format of certain chunks contained in RIFFs may very well be patented.
(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 RIFFs:
 
DaubNet RIFF Viewer for Win95: Download (freeware)
The is no generic RIFF encoder. Look at the more specific file types for encoders.

Online Resources

O'Rielly: Encyclopedia of Graphics File Formats.

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.