The preferred format for multimedia files is the Resource Interchange File Format (RIFF). The RIFF format is a tagged-file structure, and is described in detail in the file formats chapter in the Multimedia Programmer's Reference.
The multimedia file I/O services provide the following functions to support file I/O to RIFF files:
| Function | Description |
| mmioAscend | Ascends out of a RIFF file chunk to the next chunk in the file. |
| mmioCreateChunk | Creates a new chunk in a RIFF file. |
| mmioDescend | Descends into a RIFF file chunk beginning at the current file position, or searches for a specified chunk. |
| mmioFOURCC | Converts four individual characters into a four-character code. |
| mmioStringToFOURCC | Converts a null-terminated string into a four-character code. |
These functions work with the basic buffered and unbuffered file I/O services— you can open, read, and write RIFF files the same as other file types.