C# Signature:

[DllImport("winmm.dll", SetLastError=true)]
static extern UInt32 midiOutUnprepareHeader(IntPtr hMidiOut, IntPtr lpMidiOutHdr, UInt32 cbMidiOutHdr); // LD83

VB Signature:

Declare Function midiOutUnprepareHeader Lib "winmm.dll" (hMidiOut AS Intptr, lpMidiOutHdr AS IntPtr, cbMidiOutHdr) AS UInt32 ' LD83

User-Defined Types:

hMidiOut - Handle to the MIDI output device. This parameter can also be the handle of a MIDI stream cast to HMIDIOUT.

lpMidiOutHdr - Pointer to a MIDIHDR structure identifying the buffer to be cleaned up.

cbMidiOutHdr - Size, in bytes, of the MIDIHDR structure.

Returns

Returns MMRESULT. Possible values are:

MMSYSERR_NOERROR - Successful

MIDIERR_STILLPLAYING - The buffer pointed to by lpMidiOutHdr is still in the queue.

MMSYSERR_INVALHANDLE - The specified device handle is invalid.

MMSYSERR_INVALPARAM - The specified pointer or structure is invalid.

Alternative Managed API:

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Notes:

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.

Unpreparing a buffer that has not been prepared has no effect, and the function returns MMRESULT::MMSYSERR_NOERROR.

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Sample Code:

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