MidiOutProc callback function

The MidiOutProc function is the callback function for handling outgoing MIDI messages. MidiOutProc is a placeholder for the application-supplied function name. The address of the function can be specified in the callback-address parameter of the midiOutOpen function.


void CALLBACK MidiOutProc(
   HMIDIOUT  hmo,
   UINT      wMsg,
   DWORD_PTR dwInstance,
   DWORD_PTR dwParam1,
   DWORD_PTR dwParam2


  • hmo
    Handle to the MIDI device associated with the callback function.

  • wMsg
    MIDI output message.

  • dwInstance
    Instance data supplied by using the midiOutOpen function.

  • dwParam1
    Message parameter.

  • dwParam2
    Message parameter.

Return value

This function does not return a value.


Applications should not call any multimedia functions from inside the callback function, as doing so can cause a deadlock. Other system functions can safely be called from the callback.


Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]


Mmsystem.h (include Windows.h)

See also

MIDI Functions