Optional Messages for MIDI Output Device Drivers

The modMessage entry-point function for MIDI output drivers can optionally support the following messages, depending on the capabilities of the target hardware.

MODM_GETVOLUME Requests the current volume level setting. This message is used only by internal synthesizer devices.
MODM_PREPARE Requests that the driver prepare a data block for playback.
MODM_SETVOLUME Sets the volume level. This message is used only by internal synthesizer devices.
MODM_UNPREPARE Requests that a driver clean up the preparation previously done on a data block.