static extern UInt32 midiOutLongMsg(IntPtr hmo, IntPtr lpMidiOutHdr, UInt32 cbMidiOutHdr); // LD83

Declare Function midiOutLongMsg Lib "winmm.dll" (hmo AS Intptr, lpMidiOutHdr AS Intptr, cbMidiOutHdr AS UInt32) AS UInt32 ' Untested - LD83

This function is complementary to the midiOutPrepareHeader function. You must call midiOutUnprepareHeader before freeing the buffer. After passing a buffer to the device driver with the midiOutLongMsg function, you must wait until the device driver is finished with the buffer before calling midiOutUnprepareHeader.