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Resampling using ACM functions

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Hi, I''m trying to resample audio data in a buffer from 44,100Hz to 48000Hz, using the following Win32 C code:-
(olddata is unsigned char *, preinitialized)
(mmckinfoSubchunk is MMCKINFO, preinitialized)
WAVEFORMATEX wfxSrc, wfxDest;
DWORD dwOutputSize;
unsigned char *newdata;
wfxSrc.wFormatTag = WAVE_FORMAT_PCM;
wfxSrc.nChannels = 1;
wfxSrc.nSamplesPerSec = 44100;
wfxSrc.nAvgBytesPerSec = 88200;
wfxSrc.nBlockAlign = 2;
wfxSrc.wBitsPerSample = 16;
wfxDest.wFormatTag = WAVE_FORMAT_PCM;
wfxDest.nChannels = 1;
wfxDest.nSamplesPerSec = 48000;
wfxDest.wBitsPerSample = 16;
wfxDest.nBlockAlign = 2;
wfxDest.nAvgBytesPerSec = 96000;
if (acmStreamOpen(&hAcm, NULL, &wfxSrc, &wfxDest, NULL, 0, 0, 0) != 0)
	return -1;

acmStreamSize(hAcm, mmckinfoSubchunk.cksize, &dwOutputSize, ACM_STREAMSIZEF_SOURCE);
newdata = malloc(dwOutputSize);
ZeroMemory(&acmsh, sizeof(ACMSTREAMHEADER));
acmsh.cbStruct = sizeof(ACMSTREAMHEADER);
acmsh.pbSrc = olddata;
acmsh.cbSrcLength = mmckinfoSubchunk.cksize;
acmsh.pbDst = newdata;
acmsh.cbDstLength = dwOutputSize;
acmStreamPrepareHeader(hAcm, &acmsh, 0);
if (acmStreamConvert(hAcm, &acmsh, 0) != 0)
	return -1;

if (acmStreamUnprepareHeader(hAcm, &acmsh, 0) != 0)
	return -1;

acmStreamClose(hAcm, 0);
Although no errors are generated, nothing actually changes with the data either. It''s as if it just copies it straight over. Can anyone see anything wrong with this?

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