Reading ASF Files in DirectShow (Windows Media Format 11 SDK)

[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 It has been superseded by Source Reader and Sink Writer.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.]

Playback of ASF files is handled by the WM ASF Reader filter. When the WM ASF Reader reads a file, it automatically creates an output pin for each stream, including Web streams, script command streams, and any other type of arbitrary stream. In the case of multiple bit rate files, pins are created only for the currently selected streams.

The WM ASF Reader supports the DirectShow IMediaSeeking interface, which enables applications to perform temporal seeking within the file. However, playback at speeds other than 1.0 (as specified in IMediaSeeking::SetRate) is not supported.

The filter also exposes several Windows Media Format SDK interfaces as described in the following table.

Interface	How exposed	Comments
IWMDRMReader	Through IServiceProvider on filter	Provided for applications that need to play content protected by Digital Rights Management (DRM). This interface can also be used to obtain other interfaces on the Reader Object directly.
IWMHeaderInfo	QueryInterface on filter	Provided so that applications can read file and content attributes, as well as marker and script information and metadata.
IWMReaderAdvanced	QueryInterface on filter	Partially implemented on the filter so that applications can access the informational methods on the WM Reader object.
IWMReaderAdvanced2	QueryInterface on filter	Partially implemented on the filter so that applications can access the informational methods on the Reader Object.

 

The WM ASF Reader filter was first made available in DirectShow 8.0. The version of the filter that ships with DirectShow 8.1 and 9.0 supports version 7.x of the Windows Media Format SDK. The most recent version of the filter, along with the other QASF components, ships with and supports the Windows Media Format 9 Series SDK, and later versions, and it supersedes the filter in DirectX 9.0. If you install the Windows Media Format SDK after installing the DirectX 8.x or 9.x SDK, you will overwrite the DirectX version of qasf.dll with the 9 Series version. This should not present any problems except possibly in one scenario where it will result in different behavior in the DirectShow IGraphBuilder::RenderFile method. The Windows Media Format 9 Series SDK version of the WM ASF Reader is the default source filter for the .asf, .wmv, and .wma file name extensions. This means that the WM ASF Reader is automatically created and added to the filter graph by the Filter Graph Manager in methods such as IGraphBuilder::RenderFile or IGraphBuilder::AddSourceFilter when a file of this type is specified. In DirectX 9.0 and earlier, and Windows XP Service Pack 1 and earlier, the RenderFile method uses the older Windows Media Source Filter. This behavior was maintained to ensure backward compatibility with applications that used the Windows Media Player 6.4. For more information about the legacy Windows Media Source Filter, see the DirectShow SDK Documentation.

To play an ASF file with Windows Media–based content using the WM ASF Reader, the three primary steps are to create an instance of the Filter Graph Manager, call IGraphBuilder::RenderFile to create the graph, and then call IMediaControl::Run to play the file. The following code example is a complete program that plays an ASF file using DirectShow. To run this example, you must have the DirectX SDK installed and your build environment must be configured according to the instructions in the DirectShow SDK documentation topic "Setting Up the Build Environment." Also, you must specify a file on your computer in the call to RenderFile.

#include <dshow.h>
#include <stdio.h>

void main(void)
{
    IGraphBuilder *pGraph = NULL;
    IMediaControl *pControl = NULL;
    IMediaEvent   *pEvent = NULL;

    // Initialize the COM library.
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr))
    {
        printf("ERROR - Could not initialize COM library");
        return;
    }

    // Create the Filter Graph Manager and query for interfaces.
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
                        IID_IGraphBuilder, (void **)&pGraph);
    if (FAILED(hr))
    {
        printf("ERROR - Could not create the Filter Graph Manager.");
        return;
    }

    hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);

    // Build the graph. IMPORTANT: Change this string to a file
    // on your system.
    hr = pGraph->RenderFile(L"test.wmv", NULL);
    if (SUCCEEDED(hr))
    {
        // Run the graph.
        hr = pControl->Run();
        if (SUCCEEDED(hr))
        {
            // Wait for completion.
            long evCode;
            pEvent->WaitForCompletion(INFINITE, &evCode);

            // Note: Do not use INFINITE in a real application, because it
            // can block indefinitely.
        }
    }
    pControl->Release();
    pEvent->Release();
    pGraph->Release();
    CoUninitialize();
}

Note that the application code for this simple example never references the WM ASF Reader specifically. That filter is created, connected, run, and eventually released by the Filter Graph Manager. In many scenarios, however, you may want to configure the WM ASF Reader before beginning playback.