Microsoft KB Archive/77700

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Improving the Performance of MCI Wave Playback

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Q77700

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The information in this article applies to:


 * Microsoft Software Development Kit (SDK) for Windows version 3.1
 * Microsoft Win32 SDK, versions 3.5, 3.51, and 4.0

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SUMMARY
This article discusses two methods to improve playback performance for a series of MCI wave files in an application developed for the Microsoft Windows environment.

MORE INFORMATION
The following code fragment demonstrates opening the device and wave file at the same time. This method does not give the best performance.

  mciopen.lpstrDeviceType = (LPSTR)&quot;waveaudio&quot;; mciopen.lpstrElementName = (LPSTR)lpWavefile;

// The following two fields must be initialized or the debugging // version of MMSYSTEM will cause an unrecoverable application // error (UAE). mciopen.lpstrDeviceType = &quot;\0&quot;; mciopen.lpstrAlias = &quot;\0&quot;;

dwFlags = MCI_OPEN_TYPE | MCI_OPEN_ELEMENT;

dwRes = mciSendCommand(0, MCI_OPEN, dwFlags,                           (DWORD)(LPSTR)&mciopen);

To improve performance, open the device separately from the wave file (element) and leave the device open until the last element in the series has been played. Alternately, open and close elements but leave the global (waveaudio) device open during the entire process. The following code fragment demonstrates this process:

  // Open the waveaudio driver separate from the element. mciopen.lpstrDeviceType = (LPSTR)MCI_DEVTYPE_WAVEFORM_AUDIO; dwFlags = MCI_OPEN_TYPE; dwRes = mciSendCommand(0, MCI_OPEN, dwFlags,                           (DWORD)(LPSTR)&mciopen);

The following code fragment demonstrates using the global device ID to open the wave file separately:

  dwFlags = MCI_OPEN_ELEMENT; mciopen.lpstrElementName = (LPSTR)lpWaveName; dwRes = mciSendCommand(wGlobalDeviceID, MCI_OPEN, dwFlags,                          (DWORD)(LPSTR)&mciopen);

This allows the application to open and play wave files without incurring the performance penalty involved with opening the device. Another method to speed loading a wave file is to use the fully qualified path. For example, rather than specifying LASER.WAV, specify C:\MMWIN\MMDATA\LASER.WAV. If this is done, MCI is not required to search the directories in the MS-DOS PATH environment variable for the wave file.

Additional query words: 3.10 3.50 4.00 95 win16sdk

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