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Shell Metadata Providers

  • Článek

Starting in Windows 7, Microsoft Media Foundation exposes metadata through the IPropertyStore interface.

Metadata obtained using the process defined in this topic should only be used for read-only access. Writing data using this process is not supported. You can create an IPropertyStore object for writing purposes using a class identifier (CLSID) obtained from PSLookupPropertyHandlerCLSID.

Reading Metadata

To read metadata from a media source, perform the following steps:

  1. Get a pointer to the IMFMediaSource interface of the media source. You can use the IMFSourceResolver interface to get an IMFMediaSource pointer.
  2. Call MFGetService on the media source to get a pointer to the IPropertyStore interface. In the guidService parameter of MFGetService, specify the value MF_PROPERTY_HANDLER_SERVICE. If the source does not support the IPropertyStore interface, MFGetService returns MF_E_UNSUPPORTED_SERVICE.
  3. Call IPropertyStore methods to enumerate the metadata properties.

The following code shows these steps. Assume that DisplayProperty is a function that displays a PROPVARIANT value.

HRESULT EnumerateMetadata(IMFMediaSource *pSource)
{
    IPropertyStore *pProps = NULL;

    HRESULT hr = MFGetService(
        pSource, MF_PROPERTY_HANDLER_SERVICE, IID_PPV_ARGS(&pProps));

    if (FAILED(hr))
    {
        goto done;
    }

    DWORD cProps;

    hr = pProps->GetCount(&cProps);
    if (FAILED(hr))
    {
        goto done;
    }

    for (DWORD i = 0; i < cProps; i++)
    {
        PROPERTYKEY key;
        hr = pProps->GetAt(i, &key);
        if (FAILED(hr))
        {
            goto done;
        }

        PROPVARIANT pv;

        hr = pProps->GetValue(key, &pv);
        if (FAILED(hr))
        {
            goto done;
        }

        DisplayProperty(key, pv);
        PropVariantClear(&pv);
    }

done:
    SafeRelease(&pProps);
    return hr;
}

For a list of metadata property keys, see Metadata Properties for Media Files.

Media Metadata