waveInOpen function

The waveInOpen function opens the given waveform-audio input device for recording.


MMRESULT waveInOpen(
   LPHWAVEIN       phwi,
   UINT            uDeviceID,
   DWORD_PTR       dwCallback,
   DWORD_PTR       dwCallbackInstance,
   DWORD           fdwOpen


  • phwi
    Pointer to a buffer that receives a handle identifying the open waveform-audio input device. Use this handle to identify the device when calling other waveform-audio input functions. This parameter can be NULL if WAVE_FORMAT_QUERY is specified for fdwOpen.

  • uDeviceID
    Identifier of the waveform-audio input device to open. It can be either a device identifier or a handle of an open waveform-audio input device. You can use the following flag instead of a device identifier.

    Value Meaning
    WAVE_MAPPER The function selects a waveform-audio input device capable of recording in the specified format.


  • pwfx
    Pointer to a WAVEFORMATEX structure that identifies the desired format for recording waveform-audio data. You can free this structure immediately after waveInOpen returns.

  • dwCallback
    Pointer to a fixed callback function, an event handle, a handle to a window, or the identifier of a thread to be called during waveform-audio recording to process messages related to the progress of recording. If no callback function is required, this value can be zero. For more information on the callback function, see waveInProc.

  • dwCallbackInstance
    User-instance data passed to the callback mechanism. This parameter is not used with the window callback mechanism.

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

    Value Meaning
    CALLBACK_EVENT The dwCallback parameter is an event handle.
    CALLBACK_FUNCTION The dwCallback parameter is a callback procedure address.
    CALLBACK_NULL 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.

    If this flag is specified and the uDeviceID parameter is WAVE_MAPPER, the function opens the default communication device.

    This flag applies only when uDeviceID equals WAVE_MAPPER.

    Note  Requires Windows 7
    WAVE_FORMAT_DIRECT If this flag is specified, the ACM driver does not perform conversions on the audio data.
    WAVE_FORMAT_QUERY The function queries the device to determine whether it supports the given format, but it does not open the device.
    WAVE_MAPPED The uDeviceID parameter specifies a waveform-audio device to be mapped to by the wave mapper.


Return value

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

Return code Description

Specified resource is already allocated.


Specified device identifier is out of range.


No device driver is present.


Unable to allocate or lock memory.


Attempted to open with an unsupported waveform-audio format.



Use the waveInGetNumDevs function to determine the number of waveform-audio input devices present on the system. The device identifier specified by uDeviceID varies from zero to one less than the number of devices present. The WAVE_MAPPER constant can also be used as a device identifier.

If you choose to have a window or thread receive callback information, the following messages are sent to the window procedure or thread to indicate the progress of waveform-audio input: MM_WIM_OPEN, MM_WIM_CLOSE, and MM_WIM_DATA.

If you choose to have a function receive callback information, the following messages are sent to the function to indicate the progress of waveform-audio input: WIM_OPEN, WIM_CLOSE, and WIM_DATA.


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

Waveform Audio

Waveform Functions