Using Window Messages to Manage Waveform-Audio Playback
[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 It has been superseded by WASAPI and Audio Graphs.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 playback.
| Message | Description |
|---|---|
| MM_WOM_CLOSE | Sent when the device is closed by using the waveOutClose function. |
| MM_WOM_DONE | Sent when the device driver is finished with a data block sent by using the waveOutWrite function. |
| MM_WOM_OPEN | Sent when the device is opened by using the waveOutOpen function. |
A wParam and lParam parameter is associated with each of these messages. The wParam parameter always specifies a handle of the open waveform-audio device. For the MM_WOM_DONE message, lParam specifies a pointer to a WAVEHDR structure that identifies the completed data block. The lParam parameter is unused for the MM_WOM_CLOSE and MM_WOM_OPEN messages.
The most useful message is probably MM_WOM_DONE. When this message signals that playback of a data block is complete, you can clean up and free the data block. Unless you need to allocate memory or initialize variables, you probably do not need to process the MM_WOM_OPEN and MM_WOM_CLOSE messages.
The callback function for waveform-audio output devices is supplied by the application. For information about this callback function, see the waveOutProc function.