|
摘要：本文主要講述用Directshow進(jìn)行視頻捕捉（捕捉靜態(tài)圖像）的編程思路，并提供針對(duì)攝像頭編程的一個(gè)視頻捕捉類(lèi)CcaptureVideo和一個(gè)示例。
前言
DirectShow是微軟公司提供的一套在Windows平臺(tái)上進(jìn)行流媒體處理的開(kāi)發(fā)包，與DirectX開(kāi)發(fā)包一起發(fā)布。DirectShow為多媒體流的捕捉和回放提供了強(qiáng)有力的支持。用DirectShow開(kāi)發(fā)應(yīng)用程序，我們可以很方便地從支持WDM驅(qū)動(dòng)模型的采集卡上捕獲數(shù)據(jù)，并且進(jìn)行相應(yīng)的后期處理乃至存儲(chǔ)到文件中。
DirectShow是基于COM的，為了編寫(xiě)DirectShow應(yīng)用程序，需要了解COM客戶(hù)程序編寫(xiě)的基礎(chǔ)知識(shí)。DirectShow提供了大量的接口，但在編程中發(fā)現(xiàn)還是不夠方便，如果能構(gòu)建一個(gè)視頻捕捉類(lèi)把常用的一些動(dòng)作封裝起來(lái)，那么就更方便了。
編程思路
為了更加容易建立視頻捕捉應(yīng)用程序，DirectShow提供了一個(gè)叫做Capture Graph Builder的對(duì)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(gè)適當(dāng)?shù)囊曨l捕捉設(shè)備。選擇好設(shè)備后，為該設(shè)備創(chuàng)建Capture filter，然后調(diào)用AddFilter把Capture filter添加到Filter Graph。
如果僅僅希望用攝像頭來(lái)進(jìn)行實(shí)時(shí)監(jiān)控的話，只需要在上面的基礎(chǔ)上調(diào)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(gè)捕捉靜態(tài)圖像的方法：使用Sample Grabber filter。依次按照以下三個(gè)步驟就可以了：
第一步, 定義一個(gè)類(lèi)實(shí)現(xiàn)Sample Grabber的回調(diào)接口IsampleGrabberCB：
class CSampleGrabberCB : public ISampleGrabberCB
{
//在后面提供的類(lèi)中具體完成
}
CSampleGrabberCB mCB;
第二步、調(diào)用RenderStream依次把Still pin、Sample Grabber和系統(tǒng)默認(rèn)Renderer Filter連接起來(lái)。
第三步、配置Sample Grabber以捕獲數(shù)據(jù)。
視頻捕捉類(lèi)CCaptureVideo的具體實(shí)現(xiàn)
// CCaptureVideo視頻捕捉類(lèi)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(lèi)實(shí)現(xiàn)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(chēng)
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(chuàng)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(xiě)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(xiě)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(xiě)位圖數(shù)據(jù)
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;
//枚舉視頻撲捉設(shè)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 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 );
//設(shè)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 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 );
//設(shè)置視頻捕捉窗口
m_hWnd = hWnd ;
SetupVideoWindow();
hr = m_pMC->Run();//開(kāi)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 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;
// 創(chuàng)建IGraphBuilder接口
hr=CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&m_pGB);
// 創(chuàng)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(mǎn)整個(gè)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;
}
}
如何使用視頻捕捉類(lèi)CCaptureVideo
構(gòu)建CCaptureVideo類(lèi)以后，使用就方便多了，我們?cè)诰幊讨兄恍枰且旅嫒齻�(gè)類(lèi)成員函數(shù)就可以實(shí)現(xiàn)用攝像頭進(jìn)行視頻捕捉：
①int EnumDevices(HWND hList); //hList是下拉列表框的句柄，本函數(shù)用于枚舉當(dāng)前系統(tǒng)安裝的所有視頻捕捉設(shè)備
②HRESULT Init(int iDeviceID,HWND hWnd);//iDeviceID是視頻捕捉設(shè)備序號(hào)，hWnd是視頻捕捉窗口的句柄
③void GrabOneFrame(BOOL bGrab);//調(diào)用GrabOneFrame(true)就可以捕獲當(dāng)前的靜態(tài)圖像并保存到硬盤(pán)上
具體示例：用MFC AppWizard(exe)創(chuàng)建一個(gè)對(duì)話框應(yīng)用程序，取名為ds，給對(duì)話框添加一個(gè)下拉列表框(IDC_COMBO1)、兩個(gè)按鈕（IDC_PHOTO、IDC_HAVEALOOK）和一個(gè)Picture控件（ID:IDC_STATIC_SCREEN，Type: Rectangle，Color:Gray）。
1、使用向?qū)砑映蓡T變量
CStatic m_staticScreen; // IDC_STATIC_SCREEN
CComboBox m_ListCtrl; // IDC_COMBO1
CCaptureVideo m_cap;
2、為BOOL CDsDlg::OnInitDialog()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::OnOK()
{
//只需要四行代碼就可以進(jìn)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(tài)圖像，為照相按鈕添加如下代碼：
void CDsDlg::OnPhoto()
{
m_cap.GrabOneFrame(true);
}
運(yùn)行程序時(shí)，選定攝像頭后只需要按確定就可以了,實(shí)際效果如下圖所示：
結(jié)束語(yǔ)
本文提供的視頻捕捉類(lèi)CcaptureVideo和示例，在Win2K + DirectX9 SDK + VC6 環(huán)境下調(diào)試通過(guò)。注意：編譯時(shí)需要Strmiids.lib Quartz.lib兩個(gè)庫(kù)文件(DirectX9 SDK自帶)。
|
