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EasyScreenLive功能介绍
EasyScreenLive是一款简单、高效、稳定的集采集，编码，组播，推流和流媒体RTSP服务于一身的同屏功能组件，具低延时，高效能，低丢包等特点。目前支持Windows，Android平台，通过EasyScreenLive我们就可以避免接触到稍显复杂的音视频源采集，编码和流媒体推送以及RTSP/RTP/RTCP/RTMP服务流程，只需要调用EasyScreenLive的几个API接口，就能轻松、稳定地把流媒体音视频数据RTMP推送给EasyDSS服务器以及发布RTSPServer服务， RTSP同屏服务支持组播和单播两种模式。
LibEasyScreenLive通过GDI方式实现屏幕捕获采集
windows端最通用的屏幕捕获方式就是通过GDI（图形设备接口）获取桌面的设备上下文DC，然后将其内容转换为RGB位图，从而转换成视频帧实现屏幕的采集，GDI是一种微软较为古老的技术，其采集效率相对较低，不过实现30fps帧率的桌面采集还是绰绰有余的，而且在设备性能较差或者操作系统版本较低的系统上也能兼容。
LibEasyScreenLive通过GDI方式实现屏幕捕获采集的实现主要是通过CCaptureScreen类实现，该类声明如下：
class CCaptureScreen
{
public:CCaptureScreen(void);~CCaptureScreen(void);public://Interface Functionint SetCaptureCursor(bool bShow);int Init(HWND hShowWnd);void UnInit();int StartScreenCapture(int nCapMode = 2, int fps = 25);void StopScreenCapture();void GetCaptureScreenSize(int& nWidth, int& nHeight );//设置捕获数据回调函数void SetCaptureScreenCallback(CaptureScreenCallback callBack, void * pMaster);BOOL IsInCapturing(){return m_bCapturing;}public:
////屏幕捕获帧主函数//Use these 2 functions to create frames and free framesvoid* CaptureScreenFrame(int left,int top,int width, int height,int tempDisableRect);void FreeFrame(void*) ;void InsertHighLight(HDC hdc,int xoffset, int yoffset);//inner call functionBOOL isRectEqual(RECT a, RECT b);void SaveBitmapCopy(HDC hdc,HDC hdcbits, int x, int y, int sx, int sy);void RestoreBitmapCopy(HDC hdc,HDC hdcbits, int x, int y, int sx, int sy) ;void DeleteBitmapCopy();void NormalizeRect(LPRECT prc);void FixRectSizePos(LPRECT prc,int maxxScreen, int maxyScreen);//Mouse Capture functions HCURSOR FetchCursorHandle();HANDLE Bitmap2Dib(HBITMAP, UINT);//创建线程进行屏幕捕获int CreateCaptureScreenThread();static UINT WINAPI CaptureScreenThread(LPVOID pParam);void CaptureVideoProcess();
};
主要桌面采集流程在线程CaptureScreenThread中实现，采集线程执行体函数实现代码如下：
void CCaptureScreen::CaptureVideoProcess()
{int top=m_rcUse.top;int left=m_rcUse.left;int width=m_rcUse.right-m_rcUse.left+1;int height=m_rcUse.bottom - m_rcUse.top + 1;// [1/27/2016 SwordTwelve]//长宽做一下修正，修正为16的倍数int nDivW = width%16;int nDivH = height%16;if (nDivW<8)width -= nDivW;elsewidth += (16 - nDivW);if (nDivH<8)height -= nDivH;elseheight += (16 - nDivH);if (width>m_nMaxxScreen){width = m_nMaxxScreen;}if (height>m_nMaxyScreen){height = m_nMaxyScreen;}//设置捕获帧率int nFps = m_nFps;/*LPBITMAPINFOHEADER*/VOID* alpbi = NULL;RECT panrect_current;RECT panrect_dest;if (m_bAutopan) {panrect_current.left = left;panrect_current.top = top;panrect_current.right = left + width - 1;panrect_current.bottom = top + height - 1;}_LARGE_INTEGER nowTime;_LARGE_INTEGER lastTime;LARGE_INTEGER cpuFreq; //cpu频率timeBeginPeriod(1);QueryPerformanceFrequency(&cpuFreq);timeEndPeriod(1);//Into Capture Loopwhile (m_bCapturing){timeBeginPeriod(1);QueryPerformanceCounter(&lastTime);timeEndPeriod(1);//Autopanif ((m_bAutopan) && (width < m_nMaxxScreen) && (height < m_nMaxyScreen)){POINT xPoint;GetCursorPos(&xPoint);int extleft = ((panrect_current.right - panrect_current.left)*1)/4 + panrect_current.left;int extright = ((panrect_current.right - panrect_current.left)*3)/4 + panrect_current.left;int exttop = ((panrect_current.bottom - panrect_current.top)*1)/4 + panrect_current.top;int extbottom = ((panrect_current.bottom - panrect_current.top)*3)/4 + panrect_current.top; if (xPoint.x < extleft ) //need to pan left{panrect_dest.left = xPoint.x - width/2;panrect_dest.right = panrect_dest.left + width - 1;if (panrect_dest.left < 0) {panrect_dest.left = 0;panrect_dest.right = panrect_dest.left + width - 1;}}else if (xPoint.x > extright ) //need to pan right{ panrect_dest.left = xPoint.x - width/2; panrect_dest.right = panrect_dest.left + width - 1;if (panrect_dest.right >= m_nMaxxScreen){panrect_dest.right = m_nMaxxScreen - 1;panrect_dest.left = panrect_dest.right - width + 1; }}else {panrect_dest.right = panrect_current.right;panrect_dest.left = panrect_current.left;}if (xPoint.y < exttop ) //need to pan up{panrect_dest.top = xPoint.y - height/2;panrect_dest.bottom = panrect_dest.top + height - 1;if (panrect_dest.top < 0) {panrect_dest.top = 0;panrect_dest.bottom = panrect_dest.top + height - 1;}}else if (xPoint.y > extbottom ) { //need to pan downpanrect_dest.top = xPoint.y - height/2; panrect_dest.bottom = panrect_dest.top + height - 1;if (panrect_dest.bottom >= m_nMaxyScreen){panrect_dest.bottom = m_nMaxyScreen - 1;panrect_dest.top = panrect_dest.bottom - height + 1; }}else {panrect_dest.top = panrect_current.top;panrect_dest.bottom = panrect_current.bottom;}//Determine Pan Valuesint xdiff,ydiff;xdiff = panrect_dest.left - panrect_current.left;ydiff = panrect_dest.top - panrect_current.top;if (abs(xdiff) < m_nAutopanSpeed) {panrect_current.left += xdiff;}else{if (xdiff<0) panrect_current.left -= m_nAutopanSpeed;elsepanrect_current.left += m_nAutopanSpeed;}if (abs(ydiff) < m_nAutopanSpeed){panrect_current.top += ydiff;}else{if (ydiff<0) panrect_current.top -= m_nAutopanSpeed;elsepanrect_current.top += m_nAutopanSpeed;} panrect_current.right = panrect_current.left + width - 1;panrect_current.bottom = panrect_current.top + height - 1;alpbi=CaptureScreenFrame(panrect_current.left,panrect_current.top,width, height,0); }elsealpbi=CaptureScreenFrame(left,top,width, height,0); #if 1if (m_hMainWnd&&IsWindowVisible(m_hMainWnd)&&IsWindow(m_hMainWnd)){RECT rcClient;::GetClientRect(m_hMainWnd, &rcClient);if (rcClient.right-rcClient.left>0&&rcClient.bottom-rcClient.top>0){vdev_setrect(m_videoRender, rcClient.left, rcClient.top, rcClient.right, rcClient.bottom);// Capture Data callBack//测试显示void* buffer = NULL;int stride = 0;vdev_request (m_videoRender, &buffer, &stride);int swnew = ((VDEV_COMMON_CTXT*)m_videoRender)->sw;int shnew = ((VDEV_COMMON_CTXT*)m_videoRender)->sh;//memcpy(buffer, alpbi, width*height*3);vdev_convert(AV_PIX_FMT_BGR24, width, height, alpbi, AV_PIX_FMT_RGB32, swnew, shnew, (unsigned char**)&buffer);vdev_post (m_videoRender, clock());}}if (m_pCallback&&m_pMaster){ScreenCapDataInfo sCapScreenInfo;sCapScreenInfo.nWidth = width;sCapScreenInfo.nHeight = height;sCapScreenInfo.nDataType = 24;strcpy(sCapScreenInfo.strDataType, "RGB24");m_pCallback(m_nId, (unsigned char*)(alpbi), /*alpbi->biSizeImage*/m_dibBufferLen, 1, &sCapScreenInfo, m_pMaster);}
#endiftimeBeginPeriod(1);QueryPerformanceCounter(&nowTime);timeEndPeriod(1);if (cpuFreq.QuadPart < 1) cpuFreq.QuadPart = 1;int lInterval = (int)(((nowTime.QuadPart - lastTime.QuadPart) / (double)cpuFreq.QuadPart * (double)1000));//Slowly thread By framerateint nDelay = 1000/nFps - lInterval;#if 0char sMsg[64] = {0,};sprintf(sMsg, "lInterval = %d nFps =%d nDelay = %d\r\n", lInterval, nFps, nDelay);OutputDebugStringA( sMsg );
#endifif (nDelay>0){Sleep(nDelay);}}
}
其中，通过GDI获取屏幕DC并将其内容转换为RGB图像实现核心函数如下：
void* CCaptureScreen::CaptureScreenFrame(int left,int top,int width, int height,int tempDisableRect)
{//获取桌面屏幕设备DCHDC hScreenDC = ::GetDC(NULL);HDC hMemDC = ::CreateCompatibleDC(hScreenDC); HBITMAP hbm;hbm = CreateCompatibleBitmap(hScreenDC, width, height);HBITMAP oldbm = (HBITMAP) SelectObject(hMemDC, hbm); BitBlt(hMemDC, 0, 0, width, height, hScreenDC, left, top, SRCCOPY); //Get Cursor PosPOINT xPoint; GetCursorPos( &xPoint ); HCURSOR hcur= FetchCursorHandle();xPoint.x-=left;xPoint.y-=top;//Draw the HighLight if (m_bHighlightCursor==1){ POINT highlightPoint; highlightPoint.x = xPoint.x -64 ;highlightPoint.y = xPoint.y -64 ; InsertHighLight( hMemDC, highlightPoint.x, highlightPoint.y);}//Draw the Cursor if (m_bRecordCursor==1){ICONINFO iconinfo ; BOOL ret;ret = GetIconInfo( hcur, &iconinfo ); if (ret) {xPoint.x -= iconinfo.xHotspot;xPoint.y -= iconinfo.yHotspot;//need to delete the hbmMask and hbmColor bitmaps//otherwise the program will crash after a while after running out of resourceif (iconinfo.hbmMask) DeleteObject(iconinfo.hbmMask);if (iconinfo.hbmColor) DeleteObject(iconinfo.hbmColor);} // 修正鼠标信息 [7/19/2018 SwordTwelve] ::DrawIcon( hMemDC, xPoint.x*m_fScreenxScale, xPoint.y*m_fScreenyScale, hcur); }SelectObject(hMemDC,oldbm); void* pBM_HEADER = /*(LPBITMAPINFOHEADER)*/(Bitmap2Dib(hbm, 24)); //m_nColorBits//LPBITMAPINFOHEADER pBM_HEADER = (LPBITMAPINFOHEADER)GlobalLock(Bitmap2Dib(hbm, 24)); if (pBM_HEADER == NULL) { return NULL;} DeleteObject(hbm); DeleteDC(hMemDC); ReleaseDC(NULL,hScreenDC) ; return pBM_HEADER;
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