FourCC

A FourCC (four-character code) is an arbitrary 32-bit identifier that doubles as a vaguely-readable 4-character ASCII string. A FourCC often identifies a data format, or the type of data contained in a segment of a file.

Some definitions of the term "FourCC" restrict it to identifiers of data formats, or even more strictly, to multimedia formats. This article does not adopt such a strict definition.

Format details
FourCC is not a formal standard. Each format that uses FourCCs defines its own rules about what constitites a valid FourCC. However, there are conventions that seem to be followed fairly consistently by most formats.

FourCC code names are case-sensitive. Names shorter than 4 characters are padded on the right with spaces. A name contains only printable ASCII characters (often only letters and digits), with spaces allowed only for padding.

There is no standard for whether the letters are uppercase, lowercase, or a mix of both. Some formats use the character case for special purposes.

In files that use little-endian byte order, the characters of a FourCC may or may not be stored in reverse order.

Related formats
Uses of FourCCs include:
 * Multimedia codec identifiers (many formats: AVI, QuickTime, etc.)
 * Macintosh file types and creator codes
 * IFF - chunk identifiers, FORM types
 * RIFF - chunk identifiers
 * Boxes/atoms format - box identifiers, brands
 * PNG - chunk identifiers
 * ICNS - image types
 * ICC profile - tag signatures and types
 * PICT - application comment signatures
 * BMP - color spaces

Links

 * FourCC
 * FOURCC.org - Tracks codes used in multimedia formats