Resource Interchange File Format (RIFF)
This overview describes the Resource Interchange File Format (RIFF), which is used in .wav files. RIFF is the typical format from which audio data for XAudio2 will be loaded.
A RIFF file is composed of multiple discrete sections of data called chunks.
The type of data in a chunk is indicated by a four-character code (FOURCC) identifier. A FOURCC is a 32-bit unsigned integer created by concatenating four ASCII characters used to identify chunk types in a RIFF file. For example, the FOURCC "abcd" is represented on a little-endian system as 0x64636261. FOURCCs can contain space characters, so " abc" is a valid FOURCC. Audio files use FOURCC codes to identify audio format chunks, audio data chunks, and any other chunks specific to the audio format.
The following table shows the FOURCC identifiers that can be expected in the audio formats supported by XAudio2.
|Format||FOURCC identifiers||Additional information|
|PCM||"RIFF", "fmt" , "data"|
|ADPCM||"RIFF", "fmt", "data", "smpl", "wsmpl"||See ADPCM Overview for a description of the ADPCM-specific FOURCC identifiers.|
The FOURCC identifiers "RIFF", "fmt", and "data" are common to all of the supported formats. The following table describes the FOURCC identifiers that are found in all of the supported formats.
|"RIFF"||Standard RIFF chunk containing a file type with the value of "WAVE" or "XWMA" in the first four bytes of its data section and the other chunks in the file in the remainder of its data section.|
|"fmt"||Contains the format header for the audio file. The data in this chunk corresponds to one of the following structures: WAVEFORMATEX, WAVEFORMATEXTENSIBLE ADPCMWAVEFORMAT.|
|"data"||Contains audio data for the audio file. In XAudio2, the contents of the data chunk will be read into a buffer and passed to a source voice as the pAudioData member of an XAUDIO2_BUFFER structure.|
A RIFF file consists of a RIFF chunk containing zero or more other chunks.
The RIFF chunk has the following form:
"RIFF", fileSize, fileType, data
Where "RIFF" is the literal FOURCC code "RIFF", fileSize is a 4-byte value giving the size of the data in the file, and fileType is a FOURCC that identifies the specific file type. The value of fileSize includes the size of fileType FOURCC plus the size of the data that follows, but does not include the size of the "RIFF" FOURCC or the size of fileSize. The data consists of chunks in any order.
Other chunks have the following form:
chunkID, chunkSize, data
Where chunkID is a FOURCC that identifies the data contained in the chunk, chunkSize is a 4-byte value giving the size of the data section of the chunk, and data is zero or more bytes of data. The data is always padded to the nearest WORD boundary. chunkSize gives the size of the valid data in the chunk. It does not include the padding, the size of chunkID, or the size of chunkSize.