Service Interfaces

Some interfaces in Media Foundation must be obtained by calling IMFGetService::GetService instead of by calling QueryInterface. The GetService method works like QueryInterface, but with the following differences:

• It takes a service identifier GUID in addition to the interface identifier.
• It can return a pointer to another object that implements the interface, instead of returning a pointer to the original object that is queried.

A service is a particular interface obtained from a particular class of objects through the IMFGetService interface. The following services are defined.

You must use GetService to get the interfaces listed in this table from the objects listed in this table.

In some cases, an interface is returned as a service by one class of objects, and returned through QueryInterface by another class of objects. The reference pages for each interface indicate when to use GetService and when to use QueryInterface.

The MFGetService function is a helper function that queries an object for IMFGetService and then calls the object's GetService method.

Examples

The following example queries the Media Session for IMFGetService and gets the IMFRateControl interface.

IMFGetService *pGetService = NULL;
IMFRateControl *pRateControl = NULL;
HRESULT hr = S_OK;

hr = pMediaSession->QueryInterface(
    IID_IMFGetService, 
    (void**)&pGetService);

if (SUCCEEDED(hr))
{
    hr = pGetService->GetService(
        MF_RATE_CONTROL_SERVICE, 
        IID_IMFRateControl,
        (void**)&pRateControl);
}
if (SUCCEEDED(hr))
{
    // Use IMFRateControl. (Not shown.)
}

// Clean up.
SAFE_REELEASE(pGetService);
SAFE_RELEASE(pRateControl);

The following example is equivalent to the previous example but uses the MFGetService function.

IMFRateControl *pRateControl = NULL;
HRESULT hr = S_OK;

hr = MFGetService(
    pMediaSession, 
    MF_RATE_CONTROL_SERVICE, 
    IID_IMFRateControl, 
    (void**) &pRateCtl 
); 
if (SUCCEEDED(hr))
{
    // Use IMFRateControl. (Not shown.)
}

// Clean up.
SAFE_RELEASE(pRateControl);

Related topics

IMFGetService Interface

Media Foundation Platform APIs