Reading from a Wave File

In order to use the wrapper functions in Wave.c, you must declare the following four variables:

WAVEFORMATEX *pwfx; // Wave format info

HMMIO hmmio; // File handle

MMCKINFO mmckinfoData; // Chunk info

MMCKINFO mmckinfoParent; // Parent chunk info

The first step in reading a wave file is to call the WaveOpenFile function. This gets a handle to the file, verifies that it is in RIFF format, and gets information about the wave format. The parameters are the filename and the addresses of three of the variables you have declared:

if (WaveOpenFile(lpzFileName, &hmmio, &pwfx, &mmckinfoParent) != 0)

{

// Failure

}

Note that the wrapper functions all return zero if successful.

The next step is to call the WaveStartDataRead function, causing the file pointer to descend to the data chunk. This function also fills in the MMCKINFO structure for the data chunk, so that you know how much data is available:

if (WaveStartDataRead(&hmmio, &mmckinfoData, &mmckinfoParent) != 0)

{

// Failure

}

The application can now begin copying data from the file to a secondary sound buffer. Normally you don't create the sound buffer until you have obtained the size of the data chunk and the format of the wave. The following code creates a static buffer just large enough to hold all the data in the file.

/* It is assumed that lpds in a valid pointer

to the DirectSound object. */

LPDIRECTSOUNDBUFFER lpdsbStatic;

DSBUFFERDESC dsbdesc;

memset(&dsbdesc, 0, sizeof(DSBUFFERDESC));

dsbdesc.dwSize = sizeof(DSBUFFERDESC);

dsbdesc.dwFlags = DSBCAPS_STATIC;

dsbdesc.dwBufferBytes = mmckinfoData.cksize;

dsbdesc.lpwfxFormat = pwfx;

if FAILED(lpds->CreateSoundBuffer(&dsbdesc, &lpdsbStatic, NULL))

{

WaveCloseReadFile(&hmmio, &pwfx);

return FALSE;

}

Because in this case the application is not streaming the data but simply filling a static buffer, the entire buffer is locked from the beginning. There is no wraparound, so only a single pointer and byte count are required.

LPVOID lpvAudio1;

DWORD dwBytes1;

if FAILED(lpdsbStatic->Lock(

0, // Offset of lock start

0, // Size of lock; ignored in this case

&lpvAudio1, // Address of lock start

&dwBytes1, // Number of bytes locked

NULL, // Wraparound start; not used

NULL, // Wraparound size; not used

DSBLOCK_ENTIREBUFFER)) // Flag

{

// Error handling

WaveCloseReadFile(&hmmio, &pwfx);

.

.

.

}

The WaveReadFile function in Wave.c copies the data from the file to the buffer pointer and returns zero if successful.

UINT cbBytesRead;

if (WaveReadFile(

hmmio, // file handle

dwBytes1, // no. of bytes to read

(BYTE *) lpvAudio1, // destination

&mmckinfoData, // file chunk info

&cbBytesRead)) // actual no. of bytes read

{

// Handle failure on non-zero return

WaveCloseReadFile(&hmmio, &pwfx);

.

.

.

}

Finally, the application unlocks the buffer and closes the wave file:

lpdsbStatic->Unlock(lpvAudio1, dwBytes1, NULL, 0);

WaveCloseReadFile(&hmmio, &pwfx);

For a streaming buffer, you would typically call WaveReadFile at regular intervals determined by the current play position. (See Play Buffer Notification.) If the locked portion of the buffer wrapped around, of course, you would call WaveReadFile once for each segment of the lock.