获取Filter的三种途径

一、通过CLSID

IBaseFilter *pF = 0;
HRESULT hr = CoCreateInstance(clsid, 0, CLSCTX_INPROC_SERVER,
        IID_IBaseFilter, reinterpret_cast<void**>(&pF));

 

二、通过系统枚举器

ICreateDevEnum *pSysDevEnum = NULL;
hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER,
    IID_ICreateDevEnum, (void **)&pSysDevEnum);
if (FAILED(hr))
{
    return hr;
}

IEnumMoniker *pEnumCat = NULL;
hr = pSysDevEnum->CreateClassEnumerator(CLSID_VideoCompressorCategory, &pEnumCat, 0);

if (hr == S_OK)
{
    IMoniker *pMoniker = NULL;
    ULONG cFetched;
    while(pEnumCat->Next(1, &pMoniker, &cFetched) == S_OK)
    {
        IPropertyBag *pPropBag;
        hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag,
            (void **)&pPropBag);
        if (SUCCEEDED(hr))
        {
            VARIANT varName;
            VariantInit(&varName);
            hr = pPropBag->Read(L"FriendlyName", &varName, 0);

            IBaseFilter *pFilter;
            hr = pMoniker->BindToObject(NULL, NULL, IID_IBaseFilter,
                (void**)&pFilter);

            pPropBag->Release();
        }
        pMoniker->Release();
    }
    pEnumCat->Release();
}
pSysDevEnum->Release();

 

三、通过Filter Mapper

IFilterMapper2 *pMapper = NULL;
IEnumMoniker *pEnum = NULL;

hr = CoCreateInstance(CLSID_FilterMapper2,
    NULL, CLSCTX_INPROC, IID_IFilterMapper2,
    (void **) &pMapper);

GUID arrayInTypes[2];
arrayInTypes[0] = MEDIATYPE_Video;
arrayInTypes[1] = MEDIASUBTYPE_dvsd;

hr = pMapper->EnumMatchingFilters(
        &pEnum,
        0,                  // Reserved.
        TRUE,               // Use exact match?
        MERIT_DO_NOT_USE+1, // Minimum merit.
        TRUE,               // At least one input pin?
        1,                  // Number of major type/subtype pairs for input.
        arrayInTypes,       // Array of major type/subtype pairs for input.
        NULL,               // Input medium.
        NULL,               // Input pin category.
        FALSE,              // Must be a renderer?
        TRUE,               // At least one output pin?
        0,                  // Number of major type/subtype pairs for output.
        NULL,               // Array of major type/subtype pairs for output.
        NULL,               // Output medium.
        NULL);              // Output pin category.

IMoniker *pMoniker;
ULONG cFetched;
while (pEnum->Next(1, &pMoniker, &cFetched) == S_OK)
{
    IPropertyBag *pPropBag = NULL;
    hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag,
       (void **)&pPropBag);

    if (SUCCEEDED(hr))
    {
        VARIANT varName;
        VariantInit(&varName);
        hr = pPropBag->Read(L"FriendlyName", &varName, 0);
        VariantClear(&varName);

        IBaseFilter *pFilter;
        hr = pMoniker->BindToObject(NULL, NULL, IID_IBaseFilter, (void**)&pFilter);
        pPropBag->Release();
    }
    pMoniker->Release();
}

pMapper->Release();
pEnum->Release();

 

第一种方法是最直接的，也最简单，只是当不清楚CLSID的时候。就不得不用后面两种方法。

另外一种方法和第三中方法都是使用枚举器枚举Filter。通过匹配Filter的属性来得到Filter，它们不同之处在于：另外一种通过确定的种类获得枚举器，第三种通过媒体类型获得枚举器。

获得枚举器以后的步骤是同样的。

这三种方法最经常使用的是另外一种。