摘要：本文主要講述用Directshow進行視頻捕捉（捕捉靜態圖像）的編程思路，并提供針對攝像頭編程的一個視頻捕捉類CcaptureVideo和一個示例。
前言
DirectShow是微軟公司提供的一套在Windows平臺上進行流媒體處理的開發包，與DirectX開發包一起發布。DirectShow為多媒體流的捕捉和回放提供了強有力的支持。用DirectShow開發應用程序，我們可以很方便地從支持WDM驅動模型的采集卡上捕獲數據，并且進行相應的后期處理乃至存儲到文件中。
DirectShow是基于COM的，為了編寫DirectShow應用程序，需要了解COM客戶程序編寫的基礎知識。DirectShow提供了大量的接口，但在編程中發現還是不夠方便，如果能構建一個視頻捕捉類把常用的一些動作封裝起來，那么就更方便了。
編程思路
為了更加容易建立視頻捕捉應用程序，DirectShow提供了一個叫做Capture Graph Builder的對象，Capture Graph Builder提供IcaptureGraphBuilder2接口，該接口可以建立和控制Capture Graph。
建立視頻捕捉程序，必須首先獲取并初始化IcaptureGraphBuilder2接口，然后選擇一個適當的視頻捕捉設備。選擇好設備后，為該設備創建Capture filter，然后調用AddFilter把Capture filter添加到Filter Graph。
如果僅僅希望用攝像頭來進行實時監控的話，只需要在上面的基礎上調用ICaptureGraphBuilder2::RenderStream就可以了：
ICaptureGraphBuilder2 *pBuild; // Capture Graph Builder
//省略初始化部分代碼
IBaseFilter *pCap; // Video capture filter.
//省略初始化和添加到Filter Graph部分代碼
pBuild->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, pCap, NULL, NULL);?
DirectShow提供了一個捕捉靜態圖像的方法：使用Sample Grabber filter。依次按照以下三個步驟就可以了：
第一步, 定義一個類實現Sample Grabber的回調接口IsampleGrabberCB：?
class CSampleGrabberCB : public ISampleGrabberCB
{?
//在后面提供的類中具體完成
}
CSampleGrabberCB mCB;?
第二步、調用RenderStream依次把Still pin、Sample Grabber和系統默認Renderer Filter連接起來。
第三步、配置Sample Grabber以捕獲數據。
視頻捕捉類CCaptureVideo的具體實現
// CCaptureVideo視頻捕捉類頭文件
/
#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_)
//-------------------------------------------------------------------
// CCaptureVideo視頻捕捉類實現文件CaptureVideo.cpp
//-------------------------------------------------------------------
// CaptureVideo.cpp: implementation of the CCaptureVideo class.
//
/
#include "stdafx.h"
#include "CaptureVideo.h"
#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#define new DEBUG_NEW
#endif
BOOL bOneShot=FALSE;//全局變量
class CSampleGrabberCB : public ISampleGrabberCB
{public:long lWidth;long lHeight;TCHAR m_szFileName[MAX_PATH];// 位圖文件名稱CSampleGrabberCB( ){strcpy(m_szFileName, "c:\\donaldo.bmp");} STDMETHODIMP_(ULONG) AddRef() { return 2; }STDMETHODIMP_(ULONG) Release() { return 1; }STDMETHODIMP QueryInterface(REFIID riid, void ** 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;
}
//創建位圖文件
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;// 寫文件頭 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 );// 寫位圖格式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 );// 寫位圖數據WriteFile( hf, pBuffer, lBufferSize, &dwWritten, NULL );CloseHandle( hf );return 0;}
};
CSampleGrabberCB mCB;
//
// Construction/Destruction
//
CCaptureVideo::CCaptureVideo()
{//COM Library Intializationif(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 playbackif(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;//枚舉視頻撲捉設備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 inif(!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 grabberhr = 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 );//設置視頻格式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 pinhr = 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 );//設置視頻捕捉窗口m_hWnd = hWnd ; SetupVideoWindow();hr = m_pMC->Run();//開始視頻捕捉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 devicesCComPtr<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;// 創建IGraphBuilder接口hr=CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&m_pGB);// 創建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){//讓圖像充滿整個窗口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 tidiermt.cbFormat = 0;mt.pbFormat = NULL;}if (mt.pUnk != NULL) {mt.pUnk->Release();mt.pUnk = NULL;}
}
如何使用視頻捕捉類CCaptureVideo
構建CCaptureVideo類以后，使用就方便多了，我們在編程中只需要是要下面三個類成員函數就可以實現用攝像頭進行視頻捕捉：
①int EnumDevices(HWND hList); //hList是下拉列表框的句柄，本函數用于枚舉當前系統安裝的所有視頻捕捉設備
②HRESULT Init(int iDeviceID,HWND hWnd);//iDeviceID是視頻捕捉設備序號，hWnd是視頻捕捉窗口的句柄
③void GrabOneFrame(BOOL bGrab);//調用GrabOneFrame(true)就可以捕獲當前的靜態圖像并
保存
到硬盤上
具體示例：用MFC AppWizard(exe)創建一個對話框應用程序，取名為ds，給對話框添加一個下拉列表框(IDC_COMBO1)、兩個按鈕（IDC_PHOTO、IDC_HAVEALOOK）和一個Picture控件（ID:IDC_STATIC_SCREEN，Type: Rectangle，Color:Gray）。
1、使用向導添加成員變量
CStatic m_staticScreen; // IDC_STATIC_SCREEN
CComboBox m_ListCtrl; // IDC_COMBO1
CCaptureVideo m_cap;?
2、為BOOL CDsDlg::On
InitDialog()添加如下代碼：
// TODO: Add extra initialization here
m_cap.EnumDevices (m_ListCtrl);
m_ListCtrl.SetCurSel (0);?
3、為確定按鈕添加代碼如下：
void CDsDlg::On
OK()?
{
//只需要四行代碼就可以進行視頻捕捉了
UpdateData();
HWND hWnd = m_staticScreen.GetSafeHwnd() ;?
HRESULT hr = m_cap.Init(m_ListCtrl.GetCurSel (),hWnd);
GetDlgItem(IDOK)->EnableWindow(FALSE);
}?
4、如果希望捕捉靜態圖像，為照相按鈕添加如下代碼：
void CDsDlg::On
Photo()?
{
m_cap.GrabOneFrame(true);
}?
運行程序時，選定攝像頭后只需要按確定就可以了,實際效果如下圖所示：?
結束語
本文提供的視頻捕捉類CcaptureVideo和示例，在Win2K + DirectX9 SDK + VC6 環境下調試通過。注意：編譯時需要Strmiids.lib Quartz.lib兩個庫文件(DirectX9 SDK自帶)。
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