DShow中实现抓图的几种方法.doc

DShow中实现抓图的几种方法1加入Sample Grabber Filter当我们加入Sample Grabber Filter的时候，我们可以直接调用其接口（interface）ISampleGrabber。该接口可以获取经过该Filter的单独的Media Samples。详情请参见DXSDK。 1.1 派生出自己的Sample Grabber从ISampleGrabberCB中派生出自己的类，然后实现其虚函数，详情请参见SDK中的示例程序(DXSDK ROOTSamplesC+DirectShowEditingGrabBitmaps)。 1.2 直接调用Sample Grabber Filter的接口如果我们在播放的过程中动态的加入Filter的话，操作和效率都不乐观。所以我采用下面的方法： 该方法传递的是时间，不是在播放的时候动态加入Filter然后截图，而是另外打开源文件进行操作。 A）。申明以下接口： A）。申明以下接口： #001 IGraphBuilder *pGraph = NULL; /for graph builder #002 IMediaControl *pControl = NULL; /media control #003 IMediaSeeking *pSeeking = NULL; /media seeking #004 IMediaEventEx *pEvent = NULL; /media envent #005 IBaseFilter *pNullFilter =NULL;/for holding the Sample grabber FilterB）。初始化接口： #001 JIF(CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC, #002 IID_IGraphBuilder, (void *)&pGraph); #003 #004 JIF(CoCreateInstance(CLSID_NullRenderer, NULL, CLSCTX_INPROC, #005 IID_IBaseFilter, (void *)&pNullFilter); #006 JIF(pGraph-QueryInterface(IID_IMediaControl,(void *)&pControl); #007 JIF(pGraph-QueryInterface(IID_IMediaSeeking, (void *)&pSeeking); #008 JIF(pGraph-QueryInterface(IID_IMediaEvent, (void *)&pEvent); C）。创建Sample Grabber #001 / Create the Sample Grabber. #002 IBaseFilter *pGrabberF = NULL; #003 JIF(CoCreateInstance(CLSID_SampleGrabber,NULL, CLSCTX_INPROC_SERVER, #004 IID_IBaseFilter, (void*)&pGrabberF); #005 #006 JIF(pGraph-AddFilter(pGrabberF, LSample Grabber); #007 JIF(pGraph-AddFilter(pNullFilter, LNull Render Filter); #008 #009 ISampleGrabber *pGrabber; #010 JIF(pGrabberF-QueryInterface(IID_ISampleGrabber, (void*)&pGrabber); 设置Sample Grabber的媒体格式：调用SetMediaType,该函数接受一个AM_MEDIA_TYPE的结构，主要是设置该结构中的majortype，和subtype域。 D）。添加Source Filter： #001 IBaseFilter *pSrc; #002 JIF(pGraph-AddSourceFilter(T2W(m_szFile), LSource, &pSrc); E）。连接Grabber 和 NullRender两个Filter： #001 IPin *pOutPin; #002 hr = GetPin(pGrabberF, PINDIR_OUTPUT, &pOutPin); #003 #004 IPin *pInPin; #005 hr = GetPin(pNullFilter, PINDIR_INPUT, &pInPin); #006 #007 pGraph-Connect(pOutPin, pInPin); F）。取得当前所连接媒体的类型 #001 AM_MEDIA_TYPE mt; #002 hr = pGrabber-GetConnectedMediaType(&mt); #003 / Examine the format block. #004 VIDEOINFOHEADER *pVih; #005 if (mt.formattype = FORMAT_VideoInfo) & #006 (mt.cbFormat = sizeof(VIDEOINFOHEADER) & #007 (mt.pbFormat != NULL) ) #008 #009 pVih = (VIDEOINFOHEADER*)mt.pbFormat; #010 #011 else #012 #013 / Wrong format. Free the format block and return an error. #014 FreeMediaType(mt); #015 return VFW_E_INVALIDMEDIATYPE; #016 #017 #018 / Do buffer the samples as they pass through #019 / #020 hr = pGrabber-SetBufferSamples(TRUE); #021 #022 / Only grab one at a time, stop stream after #023 / grabbing one sample #024 / #025 hr = pGrabber-SetOneShot( TRUE ); G）。Seeking文件，使其到达要截图的时间帧 #001 pSeeking-SetPositions(pCurrentPos, #002 AM_SEEKING_AbsolutePositioning， #003 NULL, AM_SEEKING_NoPositioning ); #004 #005 pControl-Run(); #006 #007 long EvCode = 0; #008 #009 hr = pEvent-WaitForCompletion( INFINITE, &EvCode ); H）。取得当前的buffer数据 #001 / Find the required buffer size. #002 long cbBuffer = 0; #003 hr = pGrabber-GetCurrentBuffer(&cbBuffer, NULL); #004 LONGLONG currentPos; #005 pSeeking-GetCurrentPosition(¤tPos); #006 BYTE *pBuffer = new BYTEcbBuffer; #007 if (!pBuffer) #008 #009 / Out of memory. Return an error code. #010 Msg(Out of Memory); #011 #012 hr = pGrabber-GetCurrentBuffer(&cbBuffer, (long*)pBuffer); I）。写入文件 #001 / Create a file to hold the bitmap #002 HANDLE hf = CreateFile(szFilename, GENERIC_WRITE, FILE_SHARE_READ, #003 NULL, CREATE_ALWAYS, NULL, NULL ); #004 #005 if( hf = INVALID_HANDLE_VALUE ) #006 #007 / Failed to create file #008 return 0; #009 #010 #011 / Write out the file header #012 / #013 BITMAPFILEHEADER bfh; #014 memset( &bfh, 0, sizeof( bfh ) ); #015 bfh.bfType = MB; #016 bfh.bfSize = sizeof( bfh ) + cbBuffer + sizeof( BITMAPINFOHEADER ); #017 bfh.bfOffBits = sizeof(BITMAPINFOHEADER)+sizeof( BITMAPFILEHEADER ); #018 #019 DWORD Written = 0; #020 WriteFile( hf, &bfh, sizeof( bfh ), &Written, NULL ); #021 #022 / Write the bitmap format #023 / #024 BITMAPINFOHEADER bih; #025 memset( &bih, 0, sizeof( bih ) ); #026 bih.biSize = sizeof( bih ); #027 bih.biWidth = pVih-bmiHeader.biWidth; #028 bih.biHeight = pVih-bmiHeader.biHeight; #029 bih.biPlanes = pVih-bmiHeader.biPlanes; #030 bih.biBitCount = pVih-bmiHeader.biBitCount; #031 #032 Written = 0; #033 #034 WriteFile( hf, &bih, sizeof( bih ), &Written, NULL ); #035 #036 / Write the bitmap bits #037 / #038 Written = 0; #039 WriteFile( hf, pBuffer, cbBuffer, &Written, NULL ); #040 FreeMediaType(mt); #041 CloseHandle(hf); J）。释放资源 #001 pControl-Stop();#002 SAFE_RELEASE(pControl); #003 SAFE_RELEASE(pSeeking); #004 SAFE_RELEASE(pEvent); #005 SAFE_RELEASE(pSrc); #006 SAFE_RELEASE(pNullFilter); #007 SAFE_RELEASE(pGrabber); #008 SAFE_RELEASE(pGrabberF); #009 SAFE_RELEASE(pGraph); K）。其实我们可以不用NullRender，而是用IVideoWindow接口来实现。如果是那样的话，首先申明IVideoWindow *pVideo = NULL;将pVideo加入到Filter Graph中 #001 JIF(pGraph-QueryInterface(IID_IVideoWindow,(void*)&pVideo); #002 hr = pGraph-Render(pOutPin); #003 if (pVideo) #004 #005 hr = pVideo-put_AutoShow(OAFALSE); #006 通过IBasicVideo：GetCurrentImage接口对于该接口，Video Renderer和Video Mixing Renderer（VMR）有不同的实现。 A）。Video Renderer 如果该Renderer使用了DDraw加速的话，该调用会失败。在调用该接口的时候，必须首先暂停Renderer（可以通过IMediaControl：Pause（）暂停，如果不能确信该操作是否成功，应该调用IMediaControl:GetState()判断状态）。 B）。Video Mixing Renderer 对于VMR，该方法都会成功（不管是否运用了DDraw加速，也不管是否是暂停状态），此时对于它所有的状态（running， stopped， or paused）都适用。 函数Grabber代码如下（调用该函数的时候应该先将媒体文件暂停，原因上面已经说了）： #001 bool Grabber(IBasicVideo mBasicVideo, TCHAR *szFilename) #002 #003 if (mBasicVideo) #004 #005 long bitmapSize = 0; #006 if(SUCCEEDED(mBasicVideo-GetCurrentImage(&bitmapSize, 0) #007 #008 /if语句里面的操作时取得buffer的size。 #009 /当我们在布确定image buffer的大小的情况下，我们给 #010 /GetCurrentImage的第二个参数传递0或者NULL，取得buffer的 #011 /大小供以后使用。 #012 bool pass = false; #013 unsigned char * buffer = new unsigned charbitmapSize; #014 if(SUCCEEDED(mBasicVideo-GetCurrentImage(&bitmapSize,(long*)buffer) #015 #016 /此时已经用到刚才所取得的大小（分配空间） #017 BITMAPFILEHEADERhdr; /Bitmap的头信息 #018 LPBITMAPINFOHEADERlpbi; / Bitmap的文件信息（包括数据） #019 #020 lpbi = (LPBITMAPINFOHEADER)buffer; #021 #022 int nColors = 1 biBitCount; #023 if (nColors 256) #024 nColors = 0; #025 #026 hdr.bfType= (WORD) (M biSize #031 CFile bitmapFile(outFile, CFile:modeReadWrite | CFile:modeCreate | CFile:typeBinary); #032 bitmapFile.Write(&hdr, sizeof(BITMAPFILEHEADER); #033 bitmapFile.Write(buffer, bitmapSize); #034 bitmapFile.Close(); #035 pass = true; #036 #037 delete buffer; /数据用过之后记得要释放空间 #038 return true; #039 #040 #041 #042 return false; #043 IMediaDet接口IMediaDet接口可以取得媒体文件的信息。SDK里面的示例代码（没有写入文件）： #001 long size; #002 /取得图像帧的大小，给GetBitmapBits的第三个参数传递0 or NULL #003 hr = pDet-GetBitmapBits(0, &size, 0, width, height); #004 if(SUCCEEDED(hr) #005 #006 char *pBuffer = new charsize; #007 if(!pBuffer) #008 #009 return E_OUTOFMEMORY; #010 #011 #012 try #013 #014 hr = pDet-GetbitmapsBits(0, 0, pBuffer, width, height); #015 #016 catch(.) #017 #018 delete pBuffer; #019 throw; #020 #021 #022 if(SUCCEEDED(hr) #023