About RIFF
The basic building block of a RIFF file is a chunk. A chunk is a logical unit of data. Each chunk contains the following fields:
- A four-character code (FOURCC) specifying the chunk identifier. Conventionally, this is uppercase for registered chunk types, and lowercase otherwise.
- A DWORD value specifying the size of the data member in the chunk.
- The data.
A chunk contained in another chunk is a subchunk. The only chunks allowed to contain subchunks are those with a chunk identifier of RIFF or LIST.
The first chunk in a file must be identified as RIFF. All other chunks in the file are subchunks of this chunk. RIFF chunks are also called forms.
A LIST chunk is a grouping of subchunks. Some of these subchunks might appear multiple times, but a LIST is not an array. The terminology can be confusing. You might expect the chunk labeled <part-list>, for example, to be a list of musical parts. In fact, it is a list of the elements of a "part" chunk, which describes a single part.
RIFF chunks include an additional field in the first 4 bytes of the data field. This additional field provides the form type of the chunk. The form type is a four-character code identifying the format of the data stored in the file. For example, DirectMusic styles have the form type DMST.
LIST chunks also include an additional field in the first 4 bytes of the data field. This field contains the list type of the field. The list type is a four-character code identifying the contents of the list. For example, DirectMusic styles have a LIST chunk with a list type of "part" that contains data pertaining to a particular part (instrument track) in the performance.
Note Every four-character code used in DirectMusic files has a corresponding macro in Dmusicf.h. For example, the FOURCC for DMST is returned by the DMUS_FOURCC_STYLE_FORM macro.
For more information on RIFF files in general, see Resource Interchange File Format Services in the Platform SDK documentation.