Sending System-Exclusive Messages
MIDI system-exclusive messages are the only MIDI messages that will not fit into a single doubleword value. System-exclusive messages can be any length. Windows provides the midiOutLongMsg function for sending system-exclusive messages to MIDI output devices. To specify MIDI system-exclusive data blocks, use the MIDIHDR structure.
After you send a system-exclusive data block using midiOutLongMsg, you must wait until the device driver is finished with the data block before freeing it. If you are sending multiple data blocks, you must monitor the completion of each data block so you know when to send additional blocks. For information about different techniques for monitoring data-block completion, see Managing MIDI Data Blocks.
Note Any MIDI status byte other than a system-real-time message will terminate a system-exclusive message. If you are using multiple data blocks to send a single system-exclusive message, do not send any MIDI messages other than system-real-time messages between data blocks.