private const uint MIDICAPS_STREAM = 8;      // driver supports midiStreamOut directly

static extern Int32 midiStreamOut(IntPtr hMidiStream, MIDIHDR lpMidiHdr, uint cbMidiHdr);

Declare Function midiStreamOut Lib "winmm.dll" (ByVal hMidiStream As IntPtr, ByVal lpMidiHdr As MIDIHDR, ByVal cbMidiHdr As UInteger) As Integer