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Using Window Messages to Manage Waveform-Audio Recording

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[The feature associated with this page, Waveform Audio, is a legacy feature. It has been superseded by WASAPI and Audio Graphs. WASAPI and Audio Graphs have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use WASAPI and Audio Graphs instead of Waveform Audio, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The following messages can be sent to a window procedure function for managing waveform-audio recording.

Message Description
MM_WIM_CLOSE Sent when the device is closed by using the waveInClose function.
MM_WIM_DATA Sent when the device driver is finished with a buffer sent by using the waveInAddBuffer function.
MM_WIM_OPEN Sent when the device is opened by using the waveInOpen function.

 

The lParam parameter of MM_WIM_DATA specifies a pointer to a WAVEHDR structure that identifies the buffer. This buffer might not be completely filled with waveform-audio data; recording can stop before the buffer is filled. Use the dwBytesRecorded member of the WAVEHDR structure to determine the amount of valid data present in the buffer.

The most useful message is probably MM_WIM_DATA. When your application finishes using the data block sent by the device driver, you can clean up and free the data block. Unless you need to allocate memory or initialize variables, you probably do not need to use the MM_WIM_OPEN and MM_WIM_CLOSE messages.

The callback function for waveform-audio input devices is supplied by the application. For information about this callback function, see the waveInProc function.

Recording Waveform Audio