Reading from One Stream and Writing to Another

The following example reads data from a stream, compresses it into a new stream, and writes the compressed data into a stream of a new file.

// SaveSmall - copies a stream of data from one file, compresses

// the stream, and writes the compressed stream to a new file.

// ps stream interface pointer

// lpFilename - new AVI file to build

oid SaveSmall(PAVISTREAM ps, LPSTR lpFilename)

{

PAVIFILE pf;

PAVISTREAM psSmall;

HRESULT hr;

AVISTREAMINFO strhdr;

BITMAPINFOHEADER bi;

BITMAPINFOHEADER biNew;

LONG lStreamSize;

LPVOID lpOld;

LPVOID lpNew;

// Determine the size of the format data using

// AVIStreamFormatSize.

AVIStreamFormatSize(ps, 0, &lStreamSize);

if (lStreamSize > sizeof(bi)) // Format too large?

return;

lStreamSize = sizeof(bi);

hr = AVIStreamReadFormat(ps, 0, &bi, &lStreamSize); // Read format

if (bi.biCompression != BI_RGB) // Wrong compression format?

return;

hr = AVIStreamInfo(ps, &strhdr, sizeof(strhdr));

// Create new AVI file using AVIFileOpen.

hr = AVIFileOpen(&pf, lpFilename, OF_WRITE | OF_CREATE, NULL);

if (hr != 0)

return;

// Set parameters for the new stream.

biNew = bi;

biNew.biWidth /= 2;

biNew.biHeight /= 2;

biNew.biSizeImage = ((((UINT)biNew.biBitCount * biNew.biWidth
+ 31)&~31) / 8) * biNew.biHeight;

SetRect(&strhdr.rcFrame, 0, 0, (int) biNew.biWidth,
(int) biNew.biHeight);

// Create a stream using AVIFileCreateStream.

hr = AVIFileCreateStream(pf, &psSmall, &strhdr);

if (hr != 0) { //Stream created OK? If not, close file.

AVIFileRelease(pf);

return;

}

// Set format of new stream using AVIStreamSetFormat.

hr = AVIStreamSetFormat(psSmall, 0, &biNew, sizeof(biNew));

if (hr != 0) {

AVIStreamRelease(psSmall);

AVIFileRelease(pf);

return;

}

// Allocate memory for the bitmaps.

lpOld = GlobalAllocPtr(GMEM_MOVEABLE, bi.biSizeImage);

lpNew = GlobalAllocPtr(GMEM_MOVEABLE, biNew.biSizeImage);

// Read the stream data using AVIStreamRead.

for (lStreamSize = AVIStreamStart(ps); lStreamSize <
AVIStreamEnd(ps); lStreamSize++) {

hr = AVIStreamRead(ps, lStreamSize, 1, lpOld, bi.biSizeImage,
NULL, NULL);

// Place error check here.

// Compress the data.

CompressDIB(&bi, lpOld, &biNew, lpNew);

// Save the compressed data using AVIStreamWrite.

hr = AVIStreamWrite(psSmall, lStreamSize, 1, lpNew,
biNew.biSizeImage, AVIIF_KEYFRAME, NULL, NULL);

}

// Close the stream and file.

AVIStreamRelease(psSmall);

AVIFileRelease(pf);

}

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