midiStreamOpen function

The midiStreamOpen function opens a MIDI stream for output. By default, the device is opened in paused mode. The stream handle retrieved by this function must be used in all subsequent references to the stream.


MMRESULT midiStreamOpen(
   LPHMIDISTRM lphStream,
   LPUINT      puDeviceID,
   DWORD       cMidi,
   DWORD_PTR   dwCallback,
   DWORD_PTR   dwInstance,
   DWORD       fdwOpen


  • lphStream
    Pointer to a variable to contain the stream handle when the function returns.

  • puDeviceID
    Pointer to a device identifier. The device is opened on behalf of the stream and closed again when the stream is closed.

  • cMidi
    Reserved; must be 1.

  • dwCallback
    Pointer to a callback function, an event handle, a thread identifier, or a handle of a window or thread called during MIDI playback to process messages related to the progress of the playback. If no callback mechanism is desired, specify NULL for this parameter.

  • dwInstance
    Application-specific instance data that is returned to the application with every callback function.

  • fdwOpen
    Callback flag for opening the device. One of the following callback flags must be specified.

    Value Meaning
    CALLBACK_EVENT The dwCallback parameter is an event handle. This callback mechanism is for output only.
    CALLBACK_FUNCTION The dwCallback parameter is a callback procedure address. For the callback signature, see MidiOutProc.
    CALLBACK_NULL There is no callback mechanism. This is the default setting.
    CALLBACK_THREAD The dwCallback parameter is a thread identifier.
    CALLBACK_WINDOW The dwCallback parameter is a window handle.


Return value

Returns MMSYSERR_NOERROR if successful or an error otherwise. Possible error values include the following.

Return code Description

The specified device identifier is out of range.


The given handle or flags parameter is invalid.


The system is unable to allocate or lock memory.



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