Para buscar formatos de audio
[La característica asociada a esta página, SDK de Windows Media Format 11, es una característica heredada. Se ha reemplazado por lector de origen y escritor receptor. El lector de origen y el sistema de escritura receptor se han optimizado para Windows 10 y Windows 11. Microsoft recomienda encarecidamente que el nuevo código use lector de origen y escritor receptor en lugar del SDK de Windows Media Format 11, siempre que sea posible. Microsoft sugiere que el código existente que usa las API heredadas se reescriba para usar las nuevas API si es posible.
En el código de ejemplo siguiente se muestra cómo buscar un formato de audio que coincida con los criterios que especifique. La función FindAudioFormat acepta un puntero a una estructura WAVEFORMATEX que contiene el número de canales, bits por muestra y frecuencia de muestreo que desea usar. La función busca el formato que coincide con esos requisitos y tiene la velocidad de bits más alta que no supera el parámetro dwMaxRate . Si establece fAVSync en TRUE, la función solo valida los formatos que se pueden sincronizar con el vídeo. Para simplificar, esta función solo funciona con formatos CBR de 1 paso.
// 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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