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      



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


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


Reserved; must be 1.


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.


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


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.
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 Values

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

Value Description
MMSYSERR_BADDEVICEID The specified device identifier is out of range.
MMSYSERR_INVALPARAM The given handle or flags parameter is invalid.
MMSYSERR_NOMEM The system is unable to allocate or lock memory.


  Windows NT/2000/XP: Included in Windows NT 3.1 and later.
  Windows 95/98/Me: Included in Windows 95 and later.
  Header: Declared in Mmsystem.h; include Windows.h.
  Library: Use Winmm.lib.

See Also

Musical Instrument Digital Interface (MIDI), MIDI Functions