public static MIDIError MIDI_OutOpen(ref IntPtr handle, int deviceID, MIDIOUTPROC proc, IntPtr user) { MIDIFlags flags = MIDIFlags.MIDI_CALLBACK_FUNCTION; if (proc == null) { flags = MIDIFlags.MIDI_CALLBACK_NULL; } return(Midi.midiOutOpen(ref handle, new IntPtr(deviceID), proc, user, flags)); }