構建Graph圖常用技術

摘要：本篇文檔主要講述了Graph圖構建過程中常用的技巧
主要的內容如下：

• 1如何根據CLSID向graph中添加filter
• 2如何尋找filter閒置pin
• 3如何串連兩個Filter
• 4如何獲得filter或者pin的介面指標
• 5如何尋找和某個filter的上下相連的filter
• 6如何刪除graph中的所有filter
• 7如何利用Capture Graph Builder構建Graph圖表

1如何根據CLSID向graph中添加filter

下面的代碼示範了如何利用CLSID產生一個filter，然後將其加入到graph圖中

HRESULT AddFilterByCLSID(  IGraphBuilder *pGraph, // Pointer to the Filter Graph Manager.  const GUID& clsid, // CLSID of the filter to create.  LPCWSTR wszName, // A name for the filter.  IBaseFilter **ppF) // Receives a pointer to the filter.  {  if (!pGraph || ! ppF) return E_POINTER;  *ppF = 0;  IBaseFilter *pF = 0;  HRESULT hr = CoCreateInstance(clsid, 0, CLSCTX_INPROC_SERVER,  IID_IBaseFilter, reinterpret_cast<void**>(&pF));  if (SUCCEEDED(hr))  {  hr = pGraph->AddFilter(pF, wszName);  if (SUCCEEDED(hr))  *ppF = pF;  else  pF->Release();  }  return hr;  }

在你的應用程式中，你可以這樣用這個函數

 IBaseFilter *pMux;  hr = AddFilterByCLSID(pGraph, CLSID_AviDest, L"AVI Mux", &pMux);     if (SUCCEEDED(hr))  {  /* ... */  pMux->Release();  }

註：有些filter是不能通過with CoCreateInstance方法建立的。例如AVI Compressor Filter和WDM Video Capture filter

2如何尋找filter閒置pin

看代碼把

HRESULT GetUnconnectedPin(  IBaseFilter *pFilter, // Pointer to the filter.  PIN_DIRECTION PinDir, // Direction of the pin to find.  IPin **ppPin) // Receives a pointer to the pin.  {  *ppPin = 0;  IEnumPins *pEnum = 0;  IPin *pPin = 0;  HRESULT hr = pFilter->EnumPins(&pEnum);  if (FAILED(hr))  {  return hr;  }  while (pEnum->Next(1, &pPin, NULL) == S_OK)  {  PIN_DIRECTION ThisPinDir;  pPin->QueryDirection(&ThisPinDir);  if (ThisPinDir == PinDir)  {  IPin *pTmp = 0;  hr = pPin->ConnectedTo(&pTmp);  if (SUCCEEDED(hr)) // Already connected, not the pin we want.  {  pTmp->Release();  }  else // Unconnected, 這就是我們想要的pin，閒置pin  {  pEnum->Release();  *ppPin = pPin;  return S_OK;  }  }  pPin->Release();  }  pEnum->Release();  // Did not find a matching pin.  return E_FAIL;  }  

下面的代碼示範了如何利用上面的函數來在一個filter尋找一個輸出的閒置pin。

 IPin *pOut = NULL;  HRESULT hr = GetUnconnectedPin(pFilter, PINDIR_OUTPUT, &pOut);  if (SUCCEEDED(hr))  {  /* ... */  pOut->Release();  }

3如何串連兩個Filter

下面的函數示範了如何將一個filter的輸出pin和另一個filter的第一個閒置輸入pin進行串連。

 HRESULT ConnectFilters(  IGraphBuilder *pGraph, // Filter Graph Manager.  IPin *pOut, // Output pin on the upstream filter.  IBaseFilter *pDest) // Downstream filter.  {  if ((pGraph == NULL) || (pOut == NULL) || (pDest == NULL))  {  return E_POINTER;  }  #ifdef debug  PIN_DIRECTION PinDir;  pOut->QueryDirection(&PinDir);  _ASSERTE(PinDir == PINDIR_OUTPUT);  #endif
 //找一個閒置輸入pin  IPin *pIn = 0;  HRESULT hr = GetUnconnectedPin(pDest, PINDIR_INPUT, &pIn);  if (FAILED(hr))  {  return hr;  }  // Try to connect them.  hr = pGraph->Connect(pOut, pIn);  pIn->Release();  return hr;  }  

下面是ConnectFilters的一個重載函數，但是第二個參數是一個指向filter的指標，而不是指向pin的指標，這個函數將兩個filter串連起來。

HRESULT ConnectFilters(  IGraphBuilder *pGraph,   IBaseFilter *pSrc,   IBaseFilter *pDest)  {  if ((pGraph == NULL) || (pSrc == NULL) || (pDest == NULL))  {  return E_POINTER;  }
 // 首先在第一個filter上查詢一個輸出的pin介面  IPin *pOut = 0;  HRESULT hr = GetUnconnectedPin(pSrc, PINDIR_OUTPUT, &pOut);  if (FAILED(hr))   {  return hr;  }  //然後將它和第二個filter的輸入介面銜接。  hr = ConnectFilters(pGraph, pOut, pDest);  pOut->Release();  return hr;  }  

下面的函數示範了利用這個函數來串連AVIMux 過濾器和File Writer過濾器，這個例子也使用了AddFilterByCLSID函數。

 IBaseFilter *pMux, *pWrite;  hr = AddFilterByCLSID(pGraph, CLSID_AviDest, L"AVI Mux", &pMux);  if (SUCCEEDED(hr))  {  hr = AddFilterByCLSID(pGraph, CLSID_FileWriter, L"File Writer", &pWrite);  if (SUCCEEDED(hr))  {  hr = ConnectFilters(pGraph, pMux, pWrite);  /* Use IFileSinkFilter to set the file name (not shown). */  pWrite->Release();  }  pMux->Release();  }  

4如何獲得filter或者pin的介面指標

一般來說，我們都是通過Filter圖表管理器來進行一些操作，但是，有時候，我們也直接調用filter或者pin的一些方法，因此，我們需要擷取filter或pin的介面指標。
對於filter的介面指標，可以通過IEnumFilters來枚舉filter的指標，看下面的代碼把

HRESULT FindFilterInterface(  IGraphBuilder *pGraph, // Pointer to the Filter Graph Manager.  REFGUID iid, // IID of the interface to retrieve.  void **ppUnk) // Receives the interface pointer.  {  if (!pGraph || !ppUnk) return E_POINTER;
 HRESULT hr = E_FAIL;  IEnumFilters *pEnum = NULL;  IBaseFilter *pF = NULL;  if (FAILED(pGraph->EnumFilters(&pEnum)))  {  return E_FAIL;  }  // Query every filter for the interface.  while (S_OK == pEnum->Next(1, &pF, 0))  {  hr = pF->QueryInterface(iid, ppUnk);  pF->Release();  if (SUCCEEDED(hr))  {  break;  }  }  pEnum->Release();  return hr;  }  

用IEnumPins來獲得pin的介面指標，其實就是枚舉哦

 HRESULT FindPinInterface(  IBaseFilter *pFilter, // Pointer to the filter to search.  REFGUID iid, // IID of the interface.  void **ppUnk) // Receives the interface pointer.  {  if (!pFilter || !ppUnk) return E_POINTER;
 HRESULT hr = E_FAIL;  IEnumPins *pEnum = 0;  if (FAILED(pFilter->EnumPins(&pEnum)))  {  return E_FAIL;  }  // Query every pin for the interface.  IPin *pPin = 0;  while (S_OK == pEnum->Next(1, &pPin, 0))  {  hr = pPin->QueryInterface(iid, ppUnk);  pPin->Release();  if (SUCCEEDED(hr))  {  break;  }  }  pEnum->Release();  return hr;  }  

下面的代碼示範了如何搜尋任意的filter和pin的介面

 HRESULT FindInterfaceAnywhere(  IGraphBuilder *pGraph,   REFGUID iid,   void **ppUnk)  {  if (!pGraph || !ppUnk) return E_POINTER;  HRESULT hr = E_FAIL;  IEnumFilters *pEnum = 0;  if (FAILED(pGraph->EnumFilters(&pEnum)))  {  return E_FAIL;  }  // Loop through every filter in the graph.  IBaseFilter *pF = 0;  while (S_OK == pEnum->Next(1, &pF, 0))  {  hr = pF->QueryInterface(iid, ppUnk);  if (FAILED(hr))  {  // The filter does not expose the interface, but maybe  // one of its pins does. //調用的是上面的搜尋pin的函數  hr = FindPinInterface(pF, iid, ppUnk);  }  pF->Release();  if (SUCCEEDED(hr))  {  break;  }  }  pEnum->Release();  return hr;  }   

5如何尋找和某個filter的上下相連的filter

給你一個filter，你可以沿著graph圖找到和它相連接的filter。首先枚舉filter的pin，檢查每一個pin是否有其他的pin的和它串連，如果有就檢查串連pin屬於哪個filter，你可以通過輸入pin檢查上遊的filter，通過輸出pin來檢查下遊的filter。
下面的函數返回上遊或者下遊的和本filter串連的filter，只要有一個match，就返回。

 // Get the first upstream or downstream filter  HRESULT GetNextFilter(  IBaseFilter *pFilter, // 開始的filter  PIN_DIRECTION Dir, // 搜尋的方向 (upstream 還是 downstream)  IBaseFilter **ppNext) // Receives a pointer to the next filter.  {  if (!pFilter || !ppNext) return E_POINTER;
 IEnumPins *pEnum = 0;  IPin *pPin = 0;  HRESULT hr = pFilter->EnumPins(&pEnum);  if (FAILED(hr)) return hr;  while (S_OK == pEnum->Next(1, &pPin, 0))  {  // See if this pin matches the specified direction.  PIN_DIRECTION ThisPinDir;  hr = pPin->QueryDirection(&ThisPinDir);  if (FAILED(hr))  {  // Something strange happened.  hr = E_UNEXPECTED;  pPin->Release();  break;  }  if (ThisPinDir == Dir)  {  // Check if the pin is connected to another pin.  IPin *pPinNext = 0;  hr = pPin->ConnectedTo(&pPinNext);  if (SUCCEEDED(hr))  {  // Get the filter that owns that pin.  PIN_INFO PinInfo;  hr = pPinNext->QueryPinInfo(&PinInfo);  pPinNext->Release();  pPin->Release();  pEnum->Release();  if (FAILED(hr) || (PinInfo.pFilter == NULL))  {  // Something strange happened.  return E_UNEXPECTED;  }  // This is the filter we're looking for.  *ppNext = PinInfo.pFilter; // Client must release.  return S_OK;  }  }  pPin->Release();  }  pEnum->Release();  // Did not find a matching filter.  return E_FAIL;  }  下面示範如何使用這個函數  IBaseFilter *pF; // Pointer to some filter.  IBaseFilter *pUpstream = NULL;  if (SUCCEEDED(GetNextFilter(pF, PINDIR_INPUT, &pUpstream)))  {  // Use pUpstream ...  pUpstream->Release();  }
  

但是，一個filter可能在某個方向同時串連著兩個或者更多個filter，例如一個分割filter，就有好幾個filter與之相聯。 因此，你可能想將所有的filter通過一個集合都搜集到。下面的例子代碼就示範了如何通過CGenericList結構來實現這個方法。

 #include <streams.h> // Link to the DirectShow base class library  // Define a typedef for a list of filters.  typedef CGenericList<IBaseFilter> CFilterList;
// Forward declaration. Adds a filter to the list unless it's a duplicate.  void AddFilterUnique(CFilterList &FilterList, IBaseFilter *pNew);
// Find all the immediate upstream or downstream peers of a filter.  HRESULT GetPeerFilters(  IBaseFilter *pFilter, // Pointer to the starting filter  PIN_DIRECTION Dir, // Direction to search (upstream or downstream)  CFilterList &FilterList) // Collect the results in this list.  {  if (!pFilter) return E_POINTER;
 IEnumPins *pEnum = 0;  IPin *pPin = 0;  HRESULT hr = pFilter->EnumPins(&pEnum);  if (FAILED(hr)) return hr;  while (S_OK == pEnum->Next(1, &pPin, 0))  {  // See if this pin matches the specified direction.  PIN_DIRECTION ThisPinDir;  hr = pPin->QueryDirection(&ThisPinDir);  if (FAILED(hr))  {  // Something strange happened.  hr = E_UNEXPECTED;  pPin->Release();  break;  }  if (ThisPinDir == Dir)  {  // Check if the pin is connected to another pin.  IPin *pPinNext = 0;  hr = pPin->ConnectedTo(&pPinNext);  if (SUCCEEDED(hr))  {  // Get the filter that owns that pin.  PIN_INFO PinInfo;  hr = pPinNext->QueryPinInfo(&PinInfo);  pPinNext->Release();  if (FAILED(hr) || (PinInfo.pFilter == NULL))  {  // Something strange happened.  pPin->Release();  pEnum->Release();  return E_UNEXPECTED;  }  // 將符合的filter添加到list中  AddFilterUnique(FilterList, PinInfo.pFilter);  PinInfo.pFilter->Release();  }  }  pPin->Release();  }  pEnum->Release();  return S_OK;  }  void AddFilterUnique(CFilterList &FilterList, IBaseFilter *pNew)  {  if (pNew == NULL) return;
 POSITION pos = FilterList.GetHeadPosition();  while (pos)  {  IBaseFilter *pF = FilterList.GetNext(pos);  if (IsEqualObject(pF, pNew))  {  return;  }  }  pNew->AddRef(); // The caller must release everything in the list.  FilterList.AddTail(pNew);  }  

如何應用上面的函數呢？看看下面就知道了撒

IBaseFilter *pF; // Pointer to some filter.  CFilterList FList(NAME("MyList")); // List to hold the downstream   peers.  hr = GetPeerFilters(pF, PINDIR_OUTPUT, FList);  if (SUCCEEDED(hr)) //解析filter 的集合。  {  POSITION pos = FList.GetHeadPosition();  while (pos)  {  IBaseFilter *pDownstream = FList.GetNext(pos);  pDownstream->Release();  }  }  

6如何刪除graph中的所有filter

很簡單的，採用IFilterGraph::RemoveFilter函數

 // Stop the graph.  pControl->Stop();
// Enumerate the filters in the graph.  IEnumFilters *pEnum = NULL;  HRESULT hr = pGraph->EnumFilters(&pEnum);  if (SUCCEEDED(hr))  {  IBaseFilter *pFilter = NULL;  while (S_OK == pEnum->Next(1, &pFilter, NULL))  {  // Remove the filter.  pGraph->RemoveFilter(pFilter);  // Reset the enumerator.  pEnum->Reset();  pFilter->Release();  }  pEnum->Release();  }  

7如何利用Capture Graph Builder構建Graph圖表

Capture Graph Builder可以用來構建大多數的filter圖表，並不僅僅是捕捉graph。本文簡單介紹了如何利用Capture Graph Builder來構建graph。
Capture Graph Builder暴露了ICaptureGraphBuilder2介面指標，首先建立一個capture builder，和一個filter圖表管理器對象，然後用圖表管理器對象指標初始化Capture Graph Builder。代碼如下：

IGraphBuilder *pGraph = NULL;  ICaptureGraphBuilder2 *pBuilder = NULL;
// Create the Filter Graph Manager.  HRESULT hr = CoCreateInstance(CLSID_FilterGraph, NULL,  CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);
if (SUCCEEDED(hr))  {  // Create the Capture Graph Builder.  hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL,  CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2,   (void **)&pBuilder);  if (SUCCEEDED(hr))  {  pBuilder->SetFiltergraph (pGraph);  }  };  

串連filter
ICaptureGraphBuilder2::RenderStream方法可以同時將兩個或者三個filter串連成一個鏈（chain）。通常情況下，當每個filter只有一個輸出pin和一個輸入pin時，這個方法就才，適用。
我們現在先忽略前兩個參數，第三個參數是一個IUnknown指標，指向一個filter或者輸出pin。第五，六個參數指向IBaseFilter指標。RenderStream就將三個filter串連成一個鏈。例如，假設A，B，C 是三個filter，每個filter只有一個輸出pin和一個輸入pin。
下面的代碼可以將B串連到A上，將B串連到C上。
RenderStream(NULL, NULL, A, B, C)
所有的串連都是智能化的，如果是將兩個filter相連，你可以將中間的參數設定為NULL，
RenderStream(NULL, NULL, A, NULL, C)
你也可以調用兩次這個函數建立一個更長的鏈條。
RenderStream(NULL, NULL, A, B, C)
RenderStream(NULL, NULL, C, D, E)
如果最後的一個參數設定為NULL，這個方法就自動的為graph設定一個renderer filter。如果是視頻就設定成Video Renderer，如果是音頻就設定為DirectSoundRenderer。因此
RenderStream(NULL, NULL, A, NULL, NULL)
等價於
RenderStream(NULL, NULL, A, NULL, R)
這裡R指的是Render Filter。
如果你在第三個參數指定的是filter，而不是pin，你就要在第一二個參數裡指定使用那個輸出pin用於串連。
第一個參數只適用於捕捉filter，它指定pin的所屬種類的GUID，具體的設定可以參考Pin Property Set.，但是下面的兩個種類對於所有的filter都有效。
PIN_CATEGORY_CAPTURE
PIN_CATEGORY_PREVIEW
如果捕捉filter不支援捕捉和預覽，RenderStream方法就增加一個Smart Tee來分割資料流。
如果播放檔案，要將捕捉filter和一個mux filter串連起來，
第二個參數指明了媒體類型
MEDIATYPE_Audio
MEDIATYPE_Video
MEDIATYPE_Interleaved (DV)
查詢filter和pin的介面指標
當你建立一個graph後，也許你需要查詢graph中的filter和pin暴露的介面指標。例如，一個捕捉filter也許暴露了IAMDroppedFrames介面，它的輸出pin也許暴露了IAMStreamConfig介面。
查詢介面最簡單地方法就是使用ICaptureGraphBuilder2::FindInterface方法。這個方法遍曆整個graph的filter和pin，直到他找到合適的filter。你可以指定開始的filter，然後指定搜尋的方向，（向上搜尋還是向下搜尋）
下面的代碼在一個視頻預覽pin上搜尋IAMStreamConfig介面

 IAMStreamConfig *pConfig = NULL;  HRESULT hr = pBuild->FindInterface(  &PIN_CATEGORY_PREVIEW,   &MEDIATYPE_Video,  pVCap,   IID_IAMStreamConfig,   (void**)&pConfig  );  if (SUCCESSFUL(hr))  {  /* ... */  pConfig->Release();  }  

尋找pin
如果你需要在某個filter上查詢某個介面，可以用ICaptureGraphBuilder2::FindPin方法，代碼如下：

 IPin *pPin = NULL;  hr = pBuild->FindPin(  pCap, // Pointer to the filter to search.  PINDIR_OUTPUT, // Search for an output pin.  &PIN_CATEGORY_PREVIEW, // Search for a preview pin.  &MEDIATYPE_Video, // Search for a video pin.  TRUE, // The pin must be unconnected.   0, // Return the first matching pin (index 0).  &pPin); // This variable receives the IPin pointer.  if (SUCCESSFUL(hr))  {  /* ... */  pPin->Release();  }