This message requires that a valid hmmio handle be returned from a successful call to MMIOM_OPEN.

See mmioSetHeader for more information about header information.

The contents of the header must represent the structure that is expected by the IOProc. It does not represent the way in which data is saved by the IOProc because the IOProc might translate the data in some manner.

Examples of the standard presentation format headers that lParam1 might point to are:

• MMIMAGEHEADER, includes structure length, content, size, color type, and other information, including space for a 256-color palette.

• MMAUDIOHEADER, includes such data as structure length, content, samples per second, and sample size.

• MMMIDIHEADER, contains all pertinent information about the MIDI.

• MMMOVIEHEADER

• MMVIDEOHEADER