Using Windows Messages to Manage Waveform Audio Playback
A version of this page is also available for
4/8/2010
You can send a variety of Windows Embedded CE messages to a window procedure function to manage waveform audio playback. The following table shows these messages.
| Message | Description |
|---|---|
MM_WIM_CLOSE |
Sent when the waveOutClose or the waveInClose function closes a device. |
MM_WIM_DATA |
Sent when the device driver finishes with a data block that is sent by the waveOutWrite or the waveInAddBuffer function. |
MM_WIM_OPEN |
Sent when the waveOutOpen or the waveInOpen function opens a device. |
The MM_WIM_DATA message is the most useful message in the preceding table. When MM_WIM_DATA signals a completed data block, you can clean up and free that data block. Unless you need to allocate memory or initialize variables, you probably do not need to process the MM_WIM_OPEN message or the MM_WIM_CLOSE message.
Like other Windows-based messages, these Windows-based messages have a wParam parameter and an lParam parameter that are associated with them. The wParam parameter always specifies a handle to the open waveform audio output device. For the MM_WIM_DATA message, lParam specifies a pointer to a WAVEHDR structure. This structure identifies a completed data block. The MM_WIM_CLOSE and MM_WIM_OPEN messages do not use lParam.
The following code example shows how to process the MM_WIM_DATA message.
// WndProc-Main window procedure
LRESULT FAR PASCAL WndProc (HWND hWnd, UINT msg, WPARAM wParam,
LPARAM lParam)
{
switch (msg)
{
case MM_WIM_DATA:
// A waveform audio data block has been played and can now be
// freed.
waveOutUnprepareHeader ((HWAVEOUT)wParam, (LPWAVEHDR)lParam,
sizeof (WAVEHDR));
// Free hData memory
waveOutClose ((HWAVEOUT)wParam);
break;
}
return DefWindowProc (hWnd, msg, wParam, lParam);
}
The preceding example assumes that the application does not play multiple data blocks, so it can close the output device after playing a single data block.