To Find Audio Formats
[The feature associated with this page, Windows Media Format 11 SDK, is a legacy feature. It has been superseded by Source Reader and Sink Writer. Source Reader and Sink Writer have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use Source Reader and Sink Writer instead of Windows Media Format 11 SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]
The following example code demonstrates how to find an audio format that matches criteria you specify. The FindAudioFormat function accepts a pointer to a WAVEFORMATEX structure that contains the number of channels, bits per sample, and sample rate that you want to use. The function finds the format that matches those requirements and has the highest bit rate that does not exceed the dwMaxRate parameter. If you set fAVSync to TRUE, the function only validates formats that can be synchronized with video. For simplicity, this function only works with 1-pass CBR formats.
// This constant is used to determine if an index was found.
#define INVALID_INDEX 0xFFFF
// The FindAudioFormat function finds a compressed audio format that
// matches the criteria defined by the input parameters.
HRESULT FindAudioFormat(GUID SubType,
WAVEFORMATEX* pWaveLimits,
DWORD dwMaxRate,
BOOL fAVSync,
IWMStreamConfig** ppStreamConfig)
{
HRESULT hr = S_OK;
IWMProfileManager* pProfileMgr = NULL;
IWMCodecInfo3* pCodecInfo = NULL;
IWMStreamConfig* pStreamConfig = NULL;
IWMStreamConfig* pBestMatch = NULL;
IWMMediaProps* pProps = NULL;
WM_MEDIA_TYPE* pType = NULL;
DWORD cbType = 0;
WAVEFORMATEX* pWave = NULL;
DWORD index = 0;
DWORD cEntries = 0;
DWORD dwBestRate = 0;
DWORD PacketsPerSecond = 0;
// This value is beyond the codec indexes
// and will be used to verify success.
DWORD CodecIndex = INVALID_INDEX;
// Instantiate a profile manager object.
hr = WMCreateProfileManager(&pProfileMgr);
GOTO_EXIT_IF_FAILED(hr);
// Get the codec information interface.
hr = pProfileMgr->QueryInterface(IID_IWMCodecInfo3, (void**)&pCodecInfo);
GOTO_EXIT_IF_FAILED(hr);
// Get the number of audio codecs for which there is information.
hr = pCodecInfo->GetCodecInfoCount(WMMEDIATYPE_Audio, &cEntries);
GOTO_EXIT_IF_FAILED(hr);
// Find the index of the codec corresponding to the requested subytpe.
for(index = 0; index < cEntries; index++)
{
// Get the first format for each codec.
hr = pCodecInfo->GetCodecFormat(WMMEDIATYPE_Audio, index, 0, &pStreamConfig);
GOTO_EXIT_IF_FAILED(hr);
// Get the media properties interface.
hr = pStreamConfig->QueryInterface(IID_IWMMediaProps, (void**)&pProps);
GOTO_EXIT_IF_FAILED(hr);
// Get the size required for the media type structure.
hr = pProps->GetMediaType(NULL, &cbType);
GOTO_EXIT_IF_FAILED(hr);
// Allocate memory for the media type structure.
pType = (WM_MEDIA_TYPE*) new BYTE[cbType];
if(pType == NULL)
{
hr = E_OUTOFMEMORY;
goto Exit;
}
// Get the media type structure.
hr = pProps->GetMediaType(pType, &cbType);
GOTO_EXIT_IF_FAILED(hr);
// Check this codec against the one requested.
if(pType->subtype == SubType)
CodecIndex = index;
// The subtypes did not match. Clean up for next iteration.
SAFE_RELEASE(pStreamConfig);
SAFE_RELEASE(pProps);
SAFE_ARRAY_DELETE(pType);
// Break now if needed. Placing the break here avoids having to
// release or delete both inside and outside of the loop.
if(CodecIndex != INVALID_INDEX)
break;
} // for index
// The subtype is invalid if no codec was found that matches it.
if(CodecIndex == INVALID_INDEX)
{
hr = E_INVALIDARG;
goto Exit;
}
// Get the number of formats supported for the codec.
hr = pCodecInfo->GetCodecFormatCount(WMMEDIATYPE_Audio,
CodecIndex,
&cEntries);
GOTO_EXIT_IF_FAILED(hr);
// Loop through the formats for the codec, looking for matches.
for(index = 0; index < cEntries; index++)
{
// Get the next format.
hr = pCodecInfo->GetCodecFormat(WMMEDIATYPE_Audio,
CodecIndex,
index,
&pStreamConfig);
GOTO_EXIT_IF_FAILED(hr);
// Get the media properties interface.
hr = pStreamConfig->QueryInterface(IID_IWMMediaProps, (void**)&pProps);
GOTO_EXIT_IF_FAILED(hr);
// Get the size required for the media type structure.
hr = pProps->GetMediaType(NULL, &cbType);
GOTO_EXIT_IF_FAILED(hr);
// Allocate memory for the media type structure.
pType = (WM_MEDIA_TYPE*) new BYTE[cbType];
if(pType == NULL)
{
hr = E_OUTOFMEMORY;
goto Exit;
}
// Get the media type structure.
hr = pProps->GetMediaType(pType, &cbType);
GOTO_EXIT_IF_FAILED(hr);
// Check that the format data is present.
if(pType->cbFormat >= sizeof(WAVEFORMATEX))
pWave = (WAVEFORMATEX*)pType->pbFormat;
else
{
// The returned media type should always have an attached
// WAVEFORMATEX structure.
hr = E_UNEXPECTED;
goto Exit;
}
// Start checking data.
// Do not check particulars unless the bit rate is in range.
if((pWave->nAvgBytesPerSec * 8) > dwBestRate &&
(pWave->nAvgBytesPerSec * 8) <= dwMaxRate)
{
// Check the limits.
if((pWave->nChannels == pWaveLimits->nChannels) &&
(pWave->wBitsPerSample == pWaveLimits->wBitsPerSample) &&
(pWave->nSamplesPerSec == pWaveLimits->nSamplesPerSec))
{
// If audio/video synchronization requested, check the number
// of packets per second (Bps / BlockAlign). The bit rate is
// greater than 3200 bps, this value must be 5.
// Otherwise this value is 3.
// This is an ASF requirement.
if(fAVSync)
{
if((pWave->nAvgBytesPerSec / pWave->nBlockAlign) >=
((pWave->nAvgBytesPerSec >= 4000) ? 5.0 : 3.0))
{
// Release the previous best match.
SAFE_RELEASE(pBestMatch);
// Set this stream configuration as the new best match.
pBestMatch = pStreamConfig;
pStreamConfig->AddRef();
// Set the best bit rate.
dwBestRate = (pWave->nAvgBytesPerSec * 8);
}
} // if fAVSync
else
{
// Release the previous best match.
SAFE_RELEASE(pBestMatch);
// Set this stream configuration as the new best match.
pBestMatch = pStreamConfig;
pStreamConfig->AddRef();
// Set the best bit rate.
dwBestRate = (pWave->nAvgBytesPerSec * 8);
} // else
} // if matching limits
} // if valid bit rate
// Clean up for next iteration.
SAFE_RELEASE(pStreamConfig);
SAFE_RELEASE(pProps);
pWave = NULL;
SAFE_ARRAY_DELETE(pType);
} // for index
// If no match was found, the arguments were not valid for the codec.
if(pBestMatch == NULL)
{
hr = E_INVALIDARG;
goto Exit;
}
// Set the pointer to the stream configuration.
*ppStreamConfig = pBestMatch;
pBestMatch = NULL;
Exit:
SAFE_RELEASE(pProfileMgr);
SAFE_RELEASE(pCodecInfo);
SAFE_RELEASE(pStreamConfig);
SAFE_RELEASE(pBestMatch);
SAFE_RELEASE(pProps);
SAFE_ARRAY_DELETE(pType);
return hr;
}
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