| Microsoft DirectX 9.0 SDK Update (Summer 2004) |
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
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.
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