前言 {#前言}

　　DirectShow是微软公司提供的一套在Windows平台上进行流媒体处理的开发包，与DirectX开发包一起发布。DirectShow为多媒体流的捕捉和回放提供了强有力的支持。用DirectShow开发应用程序，我们可以很方便地从支持WDM驱动模型的采集卡上捕获数据，并且进行相应的后期处理乃至存储到文件中。

　　DirectShow是基于COM的，为了编写DirectShow应用程序，需要了解COM客户程序编写的基础知识。DirectShow提供了大量的接口，但在编程中发现还是不够方便，如果能构建一个视频捕捉类把常用的一些动作封装起来，那么就更方便了。

编程思路 {#编程思路}

　　为了更加容易建立视频捕捉应用程序，DirectShow提供了一个叫做Capture Graph Builder的对象，Capture Graph Builder提供IcaptureGraphBuilder2接口，该接口可以建立和控制Capture Graph。

　　建立视频捕捉程序，必须首先获取并初始化IcaptureGraphBuilder2接口，然后选择一个适当的视频捕捉设备。选择好设备后，为该设备创建Capture filter，然后调用AddFilter把Capture filter添加到Filter Graph。

　　如果仅仅希望用摄像头来进行实时监控的话，只需要在上面的基础上调用ICaptureGraphBuilder2::RenderStream就可以了：

|-------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | ICaptureGraphBuilder2 *pBuild; // Capture Graph Builder //省略初始化部分代码 IBaseFilter *pCap; // Video capture filter. //省略初始化和添加到Filter Graph部分代码 pBuild->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, pCap, NULL, NULL); |

　　DirectShow提供了一个捕捉静态图像的方法：使用Sample Grabber filter。依次按照以下三个步骤就可以了：

　　第一步, 定义一个类实现Sample Grabber的回调接口IsampleGrabberCB：

|-------------------|----------------------------------------------------------------------------------------------------| | 1 2 3 4 5 | class CSampleGrabberCB : public ISampleGrabberCB { 　//在后面提供的类中具体完成 } CSampleGrabberCB mCB; |

　　第二步、调用RenderStream依次把Still pin、Sample Grabber和系统默认Renderer Filter连接起来。

　　第三步、配置Sample Grabber以捕获数据。

　　视频捕捉类CCaptureVideo的具体实现

|---------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 | // CCaptureVideo视频捕捉类头文件 ///////////////////////////////////////////////////////////////////// #if !defined(AFX_CAPTUREVIDEO_H__F5345AA4_A39F_4B07_B843_3D87C4287AA0__INCLUDED_) #define AFX_CAPTUREVIDEO_H__F5345AA4_A39F_4B07_B843_3D87C4287AA0__INCLUDED_ ///////////////////////////////////////////////////////////////////// // CaptureVideo.h : header file ///////////////////////////////////////////////////////////////////// #if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 #include <atlbase.h> #include <windows.h> #include <dshow.h> #ifndef SAFE_RELEASE #define SAFE_RELEASE( x ) \ if ( NULL != x ) \ { \ 　x->Release( ); \ 　x = NULL; \ } #endif class CSampleGrabberCB; class CCaptureVideo : public CWnd { 　friend class CSampleGrabberCB; 　public: 　　void GrabOneFrame(BOOL bGrab); 　　HRESULT Init(int iDeviceID,HWND hWnd); 　　int EnumDevices(HWND hList); 　　CCaptureVideo(); 　　virtual ~CCaptureVideo(); 　private: 　　HWND m_hWnd; 　　IGraphBuilder *m_pGB; 　　ICaptureGraphBuilder2* m_pCapture; 　　IBaseFilter* m_pBF; 　　IMediaControl* m_pMC; 　　IVideoWindow* m_pVW; 　　CComPtr<ISampleGrabber> m_pGrabber; 　protected: 　　void FreeMediaType(AM_MEDIA_TYPE& mt); 　　bool BindFilter(int deviceId, IBaseFilter **pFilter); 　　void ResizeVideoWindow(); 　　HRESULT SetupVideoWindow(); 　　HRESULT InitCaptureGraphBuilder(); }; #endif // !defined(AFX_CAPTUREVIDEO_H__F5345AA4_A39F_4B07_B843_3D87C4287AA0__INCLUDED_) |

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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 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ppv){ 　　if( riid == IID_ISampleGrabberCB || riid == IID_IUnknown ){ 　　　*ppv = (void *) static_cast<ISampleGrabberCB*> ( this ); 　　　return NOERROR; 　　} 　　return E_NOINTERFACE; 　} 　STDMETHODIMP SampleCB( double SampleTime, IMediaSample * pSample ){ 　return 0; } STDMETHODIMP BufferCB( double dblSampleTime, BYTE * pBuffer, long lBufferSize ){ 　if( !bOneShot )return 0; 　　if (!pBuffer)return E_POINTER; 　SaveBitmap(pBuffer, lBufferSize); 　bOneShot = FALSE; 　return 0; } //创建位图文件 BOOL SaveBitmap(BYTE * pBuffer, long lBufferSize ) { 　HANDLE hf = CreateFile( 　m_szFileName, GENERIC_WRITE, FILE_SHARE_READ, NULL, 　CREATE_ALWAYS, NULL, NULL ); 　if( hf == INVALID_HANDLE_VALUE )return 0; 　　// 写文件头　　BITMAPFILEHEADER bfh; 　　memset( &bfh, 0, sizeof( bfh ) ); 　　bfh.bfType = 'MB'; 　　bfh.bfSize = sizeof( bfh ) + lBufferSize + sizeof( BITMAPINFOHEADER ); 　　bfh.bfOffBits = sizeof( BITMAPINFOHEADER ) + sizeof( BITMAPFILEHEADER ); 　　DWORD dwWritten = 0; 　　WriteFile( hf, &bfh, sizeof( bfh ), &dwWritten, NULL ); 　　// 写位图格式　　BITMAPINFOHEADER bih; 　　memset( &bih, 0, sizeof( bih ) ); 　　bih.biSize = sizeof( bih ); 　　bih.biWidth = lWidth; 　　bih.biHeight = lHeight; 　　bih.biPlanes = 1; 　　bih.biBitCount = 24; 　　WriteFile( hf, &bih, sizeof( bih ), &dwWritten, NULL ); 　　// 写位图数据　　WriteFile( hf, pBuffer, lBufferSize, &dwWritten, NULL ); 　　CloseHandle( hf ); 　　return 0; 　} }; CSampleGrabberCB mCB; ////////////////////////////////////////////////////////////////////// // Construction/Destruction ////////////////////////////////////////////////////////////////////// CCaptureVideo::CCaptureVideo() { 　//COM Library Intialization 　if(FAILED(CoInitialize(NULL))) /*, COINIT_APARTMENTTHREADED)))*/ 　{ 　　AfxMessageBox("CoInitialize Failed!\r\n"); 　　return; 　} 　m_hWnd = NULL; 　m_pVW = NULL; 　m_pMC = NULL; 　m_pGB = NULL; 　m_pCapture = NULL; } CCaptureVideo::~CCaptureVideo() { 　// Stop media playback 　if(m_pMC)m_pMC->Stop(); 　if(m_pVW){ 　　m_pVW->put_Visible(OAFALSE); 　　m_pVW->put_Owner(NULL); 　} 　SAFE_RELEASE(m_pCapture); 　SAFE_RELEASE(m_pMC); 　SAFE_RELEASE(m_pGB); 　SAFE_RELEASE(m_pBF); 　CoUninitialize( ); } int CCaptureVideo::EnumDevices(HWND hList) { 　if (!hList) 　　return -1; 　int id = 0; 　//枚举视频扑捉设备　ICreateDevEnum *pCreateDevEnum; 　HRESULT hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER,IID_ICreateDevEnum, (void**)&pCreateDevEnum); 　if (hr != NOERROR)return -1; 　CComPtr<IEnumMoniker> pEm; 　hr = pCreateDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory,&pEm, 0); 　if (hr != NOERROR)return -1; 　pEm->Reset(); 　ULONG cFetched; 　IMoniker *pM; 　while(hr = pEm->Next(1, &pM, &cFetched), hr==S_OK) 　{ 　　IPropertyBag *pBag; 　　hr = pM->BindToStorage(0, 0, IID_IPropertyBag, (void **)&pBag); 　　if(SUCCEEDED(hr)) 　　{ 　　　VARIANT var; 　　　var.vt = VT_BSTR; 　　　hr = pBag->Read(L"FriendlyName", &var, NULL); 　　　if (hr == NOERROR) 　　　{ 　　　　TCHAR str[2048]; 　　　　id++; 　　　　WideCharToMultiByte(CP_ACP,0,var.bstrVal, -1, str, 2048, NULL, NULL); 　　　　::SendMessage(hList, CB_ADDSTRING, 0,(LPARAM)str); 　　　　SysFreeString(var.bstrVal); 　　　} 　　　pBag->Release(); 　　} 　　pM->Release(); 　} 　return id; } HRESULT CCaptureVideo::Init(int iDeviceID, HWND hWnd) { 　HRESULT hr; 　hr = InitCaptureGraphBuilder(); 　if (FAILED(hr)){ 　　AfxMessageBox("Failed to get video interfaces!"); 　　return hr; 　} 　// Bind Device Filter. We know the device because the id was passed in 　if(!BindFilter(iDeviceID, &m_pBF))return S_FALSE; 　hr = m_pGB->AddFilter(m_pBF, L"Capture Filter"); 　// hr = m_pCapture->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, 　// m_pBF, NULL, NULL); 　// create a sample grabber 　hr = m_pGrabber.CoCreateInstance( CLSID_SampleGrabber ); 　if( !m_pGrabber ){ 　　AfxMessageBox("Fail to create SampleGrabber, maybe qedit.dll is not registered?"); 　　return hr; 　} 　CComQIPtr< IBaseFilter, &IID_IBaseFilter > pGrabBase( m_pGrabber ); 　//设置视频格式　AM_MEDIA_TYPE mt; 　ZeroMemory(&mt, sizeof(AM_MEDIA_TYPE)); 　mt.majortype = MEDIATYPE_Video; 　mt.subtype = MEDIASUBTYPE_RGB24; 　hr = m_pGrabber->SetMediaType(&mt); 　if( FAILED( hr ) ){ 　　AfxMessageBox("Fail to set media type!"); 　　return hr; 　} 　hr = m_pGB->AddFilter( pGrabBase, L"Grabber" ); 　if( FAILED( hr ) ){ 　　AfxMessageBox("Fail to put sample grabber in graph"); 　　return hr; 　} 　// try to render preview/capture pin 　hr = m_pCapture->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video,m_pBF,pGrabBase,NULL); 　if( FAILED( hr ) ) 　　hr = m_pCapture->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video,m_pBF,pGrabBase,NULL); 　　if( FAILED( hr ) ){ 　　　AfxMessageBox("Can't build the graph"); 　　　return hr; 　　} 　　hr = m_pGrabber->GetConnectedMediaType( &mt ); 　if ( FAILED( hr) ){ 　　AfxMessageBox("Failt to read the connected media type"); 　　return hr; 　} 　VIDEOINFOHEADER * vih = (VIDEOINFOHEADER*) mt.pbFormat; 　mCB.lWidth = vih->bmiHeader.biWidth; 　mCB.lHeight = vih->bmiHeader.biHeight; 　FreeMediaType(mt); 　hr = m_pGrabber->SetBufferSamples( FALSE ); 　hr = m_pGrabber->SetOneShot( FALSE ); 　hr = m_pGrabber->SetCallback( &mCB, 1 ); 　//设置视频捕捉窗口　m_hWnd = hWnd ; 　SetupVideoWindow(); 　hr = m_pMC->Run();//开始视频捕捉　if(FAILED(hr)){AfxMessageBox("Couldn't run the graph!");return hr;} 　return S_OK; } bool CCaptureVideo::BindFilter(int deviceId, IBaseFilter **pFilter) { 　if (deviceId < 0) 　return false; 　// enumerate all video capture devices 　CComPtr<ICreateDevEnum> pCreateDevEnum; 　HRESULT hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER, IID_ICreateDevEnum, (void**)&pCreateDevEnum); 　if (hr != NOERROR) 　{ 　　return false; 　} 　CComPtr<IEnumMoniker> pEm; 　hr = pCreateDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory,&pEm, 0); 　if (hr != NOERROR) 　{ 　　return false; 　} 　pEm->Reset(); 　ULONG cFetched; 　IMoniker *pM; 　int index = 0; 　while(hr = pEm->Next(1, &pM, &cFetched), hr==S_OK, index <= deviceId) 　{ 　　IPropertyBag *pBag; 　　hr = pM->BindToStorage(0, 0, IID_IPropertyBag, (void **)&pBag); 　　if(SUCCEEDED(hr)) 　　{ 　　　VARIANT var; 　　　var.vt = VT_BSTR; 　　　hr = pBag->Read(L"FriendlyName", &var, NULL); 　　　if (hr == NOERROR) 　　　{ 　　　　if (index == deviceId) 　　　　{ 　　　　　pM->BindToObject(0, 0, IID_IBaseFilter, (void**)pFilter); 　　　　} 　　　　SysFreeString(var.bstrVal); 　　　} 　　　pBag->Release(); 　　} 　　pM->Release(); 　　index++; 　} 　return true; } HRESULT CCaptureVideo::InitCaptureGraphBuilder() { 　HRESULT hr; 　// 创建IGraphBuilder接口　hr=CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&m_pGB); 　// 创建ICaptureGraphBuilder2接口　hr = CoCreateInstance (CLSID_CaptureGraphBuilder2 , NULL, CLSCTX_INPROC, IID_ICaptureGraphBuilder2, (void **) &m_pCapture); 　if (FAILED(hr))return hr; 　m_pCapture->SetFiltergraph(m_pGB); 　hr = m_pGB->QueryInterface(IID_IMediaControl, (void **)&m_pMC); 　if (FAILED(hr))return hr; 　hr = m_pGB->QueryInterface(IID_IVideoWindow, (LPVOID *) &m_pVW); 　if (FAILED(hr))return hr; 　return hr; } HRESULT CCaptureVideo::SetupVideoWindow() { 　HRESULT hr; 　hr = m_pVW->put_Owner((OAHWND)m_hWnd); 　if (FAILED(hr))return hr; 　hr = m_pVW->put_WindowStyle(WS_CHILD | WS_CLIPCHILDREN); 　if (FAILED(hr))return hr; 　ResizeVideoWindow(); 　hr = m_pVW->put_Visible(OATRUE); 　return hr; } void CCaptureVideo::ResizeVideoWindow() { 　if (m_pVW){ 　　//让图像充满整个窗口　　CRect rc; 　　::GetClientRect(m_hWnd,&rc); 　　m_pVW->SetWindowPosition(0, 0, rc.right, rc.bottom); 　} } void CCaptureVideo::GrabOneFrame(BOOL bGrab) { 　bOneShot = bGrab; } void CCaptureVideo::FreeMediaType(AM_MEDIA_TYPE& mt) { 　if (mt.cbFormat != 0) { 　　CoTaskMemFree((PVOID)mt.pbFormat); 　　// Strictly unnecessary but tidier 　　mt.cbFormat = 0; 　　mt.pbFormat = NULL; 　} 　if (mt.pUnk != NULL) { 　　mt.pUnk->Release(); 　　mt.pUnk = NULL; 　} } |

使用方法 {#使用方法}

如何使用视频捕捉类CCaptureVideo

　　构建CCaptureVideo类以后，使用就方便多了，我们在编程中只需要是要下面三个类成员函数就可以实现用摄像头进行视频捕捉：

　　①int EnumDevices(HWND hList); //hList是下拉列表框的句柄，本函数用于枚举当前系统安装的所有视频捕捉设备

　　②HRESULT Init(int iDeviceID,HWND hWnd);//iDeviceID是视频捕捉设备序号，hWnd是视频捕捉窗口的句柄

　　③void GrabOneFrame(BOOL bGrab);//调用GrabOneFrame(true)就可以捕获当前的静态图像并保存到硬盘上
　　
　　具体示例：用MFC AppWizard(exe)创建一个对话框应用程序，取名为ds，给对话框添加一个下拉列表框(IDC_COMBO1)、两个按钮（IDC_PHOTO、IDC_HAVEALOOK）和一个Picture控件（ID:IDC_STATIC_SCREEN，Type: Rectangle，Color:Gray）。

　　1、使用向导添加成员变量

|---------------|---------------------------------------------------------------------------------------------------------------| | 1 2 3 | CStatic m_staticScreen; // IDC_STATIC_SCREEN CComboBox m_ListCtrl; // IDC_COMBO1 CCaptureVideo m_cap; |

　　2、为BOOL CDsDlg::OnInitDialog()添加如下代码：

|---------------|----------------------------------------------------------------------------------------------------------| | 1 2 3 | // TODO: Add extra initialization here m_cap.EnumDevices (m_ListCtrl); m_ListCtrl.SetCurSel (0); |

　　3、为确定按钮添加代码如下：

|-------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | 1 2 3 4 5 6 7 8 | void CDsDlg::OnOK() { 　//只需要四行代码就可以进行视频捕捉了　UpdateData(); 　HWND hWnd = m_staticScreen.GetSafeHwnd() ; 　HRESULT hr = m_cap.Init(m_ListCtrl.GetCurSel (),hWnd); 　GetDlgItem(IDOK)->EnableWindow(FALSE); } |

　　4、如果希望捕捉静态图像，为照相按钮添加如下代码：

|-----------------|---------------------------------------------------------------| | 1 2 3 4 | void CDsDlg::OnPhoto() { 　m_cap.GrabOneFrame(true); } |

　　运行程序时，选定摄像头后只需要按确定就可以了。