mixerOpen

Article
12/10/2007

The mixerOpen function opens a specified mixer device and ensures that the device will not be removed until the application closes the handle.

MMRESULT mixerOpen(
  LPHMIXER  phmx,        
  UINT      uMxId,       
  DWORD_PTR dwCallback,  
  DWORD_PTR dwInstance,  
  DWORD     fdwOpen      
);

Parameters

phmx

Pointer to a variable that will receive a handle identifying the opened mixer device. Use this handle to identify the device when calling other audio mixer functions. This parameter cannot be NULL.

uMxId

Identifier of the mixer device to open. Use a valid device identifier or any HMIXEROBJ (see the mixerGetID function for a description of mixer object handles). A "mapper" for audio mixer devices does not currently exist, so a mixer device identifier of - 1 is not valid.

dwCallback

Handle to a window called when the state of an audio line and/or control associated with the device being opened is changed. Specify NULL for this parameter if no callback mechanism is to be used.

dwInstance

Reserved. Must be zero.

fdwOpen

Flags for opening the device. The following values are defined.

Value	Meaning
CALLBACK_WINDOW	The dwCallback parameter is assumed to be a window handle (HWND).
MIXER_OBJECTF_AUX	The uMxId parameter is an auxiliary device identifier in the range of zero to one less than the number of devices returned by the auxGetNumDevs function.
MIXER_OBJECTF_HMIDIIN	The uMxId parameter is the handle of a MIDI input device. This handle must have been returned by the midiInOpen function.
MIXER_OBJECTF_HMIDIOUT	The uMxId parameter is the handle of a MIDI output device. This handle must have been returned by the midiOutOpen function.
MIXER_OBJECTF_HMIXER	The uMxId parameter is a mixer device handle returned by the mixerOpen function. This flag is optional.
MIXER_OBJECTF_HWAVEIN	The uMxId parameter is a waveform-audio input handle returned by the waveInOpen function.
MIXER_OBJECTF_HWAVEOUT	The uMxId parameter is a waveform-audio output handle returned by the waveOutOpen function.
MIXER_OBJECTF_MIDIIN	The uMxId parameter is the identifier of a MIDI input device. This identifier must be in the range of zero to one less than the number of devices returned by the midiInGetNumDevs function.
MIXER_OBJECTF_MIDIOUT	The uMxId parameter is the identifier of a MIDI output device. This identifier must be in the range of zero to one less than the number of devices returned by the midiOutGetNumDevs function.
MIXER_OBJECTF_MIXER	The uMxId parameter is a mixer device identifier in the range of zero to one less than the number of devices returned by the mixerGetNumDevs function. This flag is optional.
MIXER_OBJECTF_WAVEIN	The uMxId parameter is the identifier of a waveform-audio input device in the range of zero to one less than the number of devices returned by the waveInGetNumDevs function.
MIXER_OBJECTF_WAVEOUT	The uMxId parameter is the identifier of a waveform-audio output device in the range of zero to one less than the number of devices returned by the waveOutGetNumDevs function.

Return Values

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

Value	Description
MMSYSERR_ALLOCATED	The specified resource is already allocated by the maximum number of clients possible.
MMSYSERR_BADDEVICEID	The uMxId parameter specifies an invalid device identifier.
MMSYSERR_INVALFLAG	One or more flags are invalid.
MMSYSERR_INVALHANDLE	The uMxId parameter specifies an invalid handle.
MMSYSERR_INVALPARAM	One or more parameters are invalid.
MMSYSERR_NODRIVER	No mixer device is available for the object specified by uMxId. Note that the location referenced by uMxId will also contain the value - 1.
MMSYSERR_NOMEM	Unable to allocate resources.

Remarks

Use the mixerGetNumDevs function to determine the number of audio mixer devices present in the system. The device identifier specified by uMxId varies from zero to one less than the number of devices present.

If a window is chosen to receive callback information, the MM_MIXM_LINE_CHANGE and MM_MIXM_CONTROL_CHANGE messages are sent to the window procedure function to indicate when an audio line or control state changes. For both messages, the wParam parameter is the handle of the mixer device. The lParam parameter is the line identifier for MM_MIXM_LINE_CHANGE or the control identifier for MM_MIXM_CONTROL_CHANGE that changed state.

To query for audio mixer support or a media device, use the mixerGetID function.

Requirements

**  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.

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