A FOURCC is a 32-bit quantity representing a sequence of one to four ASCII alphanumeric characters (padded on the right with blank characters). Each I/O procedure supports a specific file format. The file format and IOProc are represented by a specific FOURCC code. This permits the FOURCC to be used as an ID value, rather than the National Language Support (NLS) string-name of the file format or a file name extension.
Formats that support multiple media types require a different FOURCC for each variation. This appears as a different I/O procedure for each media type.
Note: Use the mmioIdentifyFile function to identify the four-character code if it is not available.