Step 3: Build the Filter Graph
[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]
This topic is step 3 of the tutorial Audio/Video Playback in DirectShow. The complete code is shown in the topic DirectShow Playback Example.
The next step is to build a filter graph to play the media file.
Opening a Media File
The DShowPlayer::OpenFile method opens a media file for playback. This method does the following:
- Creates a new (empty) filter graph.
- Calls IGraphBuilder::AddSourceFilter to add a source filter for the specified file.
- Renders the streams on the source filter.
HRESULT DShowPlayer::OpenFile(PCWSTR pszFileName)
{
IBaseFilter *pSource = NULL;
// Create a new filter graph. (This also closes the old one, if any.)
HRESULT hr = InitializeGraph();
if (FAILED(hr))
{
goto done;
}
// Add the source filter to the graph.
hr = m_pGraph->AddSourceFilter(pszFileName, NULL, &pSource);
if (FAILED(hr))
{
goto done;
}
// Try to render the streams.
hr = RenderStreams(pSource);
done:
if (FAILED(hr))
{
TearDownGraph();
}
SafeRelease(&pSource);
return hr;
}
Creating the Filter Graph Manager
The DShowPlayer::InitializeGraph method creates a new filter graph. This method does the following:
- Calls CoCreateInstance to create a new instance of the Filter Graph Manager.
- Queries the Filter Graph Manager for the IMediaControl and IMediaEventEx interfaces.
- Calls IMediaEventEx::SetNotifyWindow to set up event notification. For more information, see Event Notification in DirectShow.
HRESULT DShowPlayer::InitializeGraph()
{
TearDownGraph();
// Create the Filter Graph Manager.
HRESULT hr = CoCreateInstance(CLSID_FilterGraph, NULL,
CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&m_pGraph));
if (FAILED(hr))
{
goto done;
}
hr = m_pGraph->QueryInterface(IID_PPV_ARGS(&m_pControl));
if (FAILED(hr))
{
goto done;
}
hr = m_pGraph->QueryInterface(IID_PPV_ARGS(&m_pEvent));
if (FAILED(hr))
{
goto done;
}
// Set up event notification.
hr = m_pEvent->SetNotifyWindow((OAHWND)m_hwnd, WM_GRAPH_EVENT, NULL);
if (FAILED(hr))
{
goto done;
}
m_state = STATE_STOPPED;
done:
return hr;
}
Rendering the Streams
The next step is to connect the source filter to one or more renderer filters.
The DShowPlayer::RenderStreams method performs the following steps.
- Queries the Filter Graph Manager for the IFilterGraph2 interface.
- Adds a video renderer filter to the filter graph.
- Adds the DirectSound Renderer Filter to the filter graph, to support audio playback. For more information about adding filters to the filter graph, see Add a Filter by CLSID.
- Enumerates the output pins on the source filter. For more information about enumerating pins, see Enumerating Pins.
- For each pin, calls the IFilterGraph2::RenderEx method. This method connects the output pin to a renderer filter, adding intermediate filters if needed (such as decoders).
- Calls
CVideoRenderer::FinalizeGraphto finish initializing the video renderer. - Removes the DirectSound Renderer filter if that filter is not connected to another filter. This can occur if the source file does not contain an audio stream.
// Render the streams from a source filter.
HRESULT DShowPlayer::RenderStreams(IBaseFilter *pSource)
{
BOOL bRenderedAnyPin = FALSE;
IFilterGraph2 *pGraph2 = NULL;
IEnumPins *pEnum = NULL;
IBaseFilter *pAudioRenderer = NULL;
HRESULT hr = m_pGraph->QueryInterface(IID_PPV_ARGS(&pGraph2));
if (FAILED(hr))
{
goto done;
}
// Add the video renderer to the graph
hr = CreateVideoRenderer();
if (FAILED(hr))
{
goto done;
}
// Add the DSound Renderer to the graph.
hr = AddFilterByCLSID(m_pGraph, CLSID_DSoundRender,
&pAudioRenderer, L"Audio Renderer");
if (FAILED(hr))
{
goto done;
}
// Enumerate the pins on the source filter.
hr = pSource->EnumPins(&pEnum);
if (FAILED(hr))
{
goto done;
}
// Loop through all the pins
IPin *pPin;
while (S_OK == pEnum->Next(1, &pPin, NULL))
{
// Try to render this pin.
// It's OK if we fail some pins, if at least one pin renders.
HRESULT hr2 = pGraph2->RenderEx(pPin, AM_RENDEREX_RENDERTOEXISTINGRENDERERS, NULL);
pPin->Release();
if (SUCCEEDED(hr2))
{
bRenderedAnyPin = TRUE;
}
}
hr = m_pVideo->FinalizeGraph(m_pGraph);
if (FAILED(hr))
{
goto done;
}
// Remove the audio renderer, if not used.
BOOL bRemoved;
hr = RemoveUnconnectedRenderer(m_pGraph, pAudioRenderer, &bRemoved);
done:
SafeRelease(&pEnum);
SafeRelease(&pAudioRenderer);
SafeRelease(&pGraph2);
// If we succeeded to this point, make sure we rendered at least one
// stream.
if (SUCCEEDED(hr))
{
if (!bRenderedAnyPin)
{
hr = VFW_E_CANNOT_RENDER;
}
}
return hr;
}
Here is the code for the RemoveUnconnectedRenderer function, which is used in the previous example.
HRESULT RemoveUnconnectedRenderer(IGraphBuilder *pGraph, IBaseFilter *pRenderer, BOOL *pbRemoved)
{
IPin *pPin = NULL;
*pbRemoved = FALSE;
// Look for a connected input pin on the renderer.
HRESULT hr = FindConnectedPin(pRenderer, PINDIR_INPUT, &pPin);
SafeRelease(&pPin);
// If this function succeeds, the renderer is connected, so we don't remove it.
// If it fails, it means the renderer is not connected to anything, so
// we remove it.
if (FAILED(hr))
{
hr = pGraph->RemoveFilter(pRenderer);
*pbRemoved = TRUE;
}
return hr;
}
Releasing the Filter Graph
When the application exits, it must release the filter graph, as shown in the following code.
void DShowPlayer::TearDownGraph()
{
// Stop sending event messages
if (m_pEvent)
{
m_pEvent->SetNotifyWindow((OAHWND)NULL, NULL, NULL);
}
SafeRelease(&m_pGraph);
SafeRelease(&m_pControl);
SafeRelease(&m_pEvent);
delete m_pVideo;
m_pVideo = NULL;
m_state = STATE_NO_GRAPH;
}
Next: Step 4: Add the Video Renderer.
Related topics