FourCC
A fourcc (for English Four C haracter C ode ) is a four- byte long type identifier in the header data area of a container file or contained therein subunits (chunks) and outputs the format of the content to. When a container file is opened, this information is used to select the codec for decompressing or displaying the data.
A FourCC consists of four ASCII characters that mnemonic indicate the meaning. First used were FourCCs in Interchange File Format (IFF) from Electronic Arts . According to their documentation, the idea came from Apple . In the Macintosh FourCCs were used under the name OSType (also ResType ).
In contrast to file name extensions , FourCCs distinguish between uppercase and lowercase letters. The space is allowed to fill three-character mnemonics, for example " AVI " for AVI files or " fmt " for the format chunk of a WAVE audio file.
For RIFF formats, registering the FourCCs used with Microsoft ensures that they are only used once. Microsoft publishes a list of the registered character strings.