DirectXShow开发-实现视频预览和捕获静态图片功能出现的问题

[mf1983]

最近在做基于DirectXShow的视频预览及捕获静态图片的工作，使用VS2005，CLR C++开发
要完成的功能：
1 一个pictureBox中实现视频预览
2 通过button按钮事件从视频预览的video stream中捕获一张图片数据，并在另一个pictureBox中显示出来
3 捕获的同时视频预览窗口可以有暂时的停顿，捕获完毕要继续实现视频预览的功能

查阅了MSDN，也参考了DirectXShow的demo（Microsoft DirectX 9.0 SDK (Summer 2004)\Samples\C++\DirectShow目录下的Capture和Editing下的demo），采用了Sample Grabber Filter，使用SetBufferSamples( TRUE ) ;SetOneShot( FALSE )的模式.

问题是：
1 单独实现视频预览或单独实现从capture video stream中捕获一张图片都没问题
2 在预览视频的同时捕获图片出现问题，GetCurrentBuffer时出错

IMediaControl::Run之后使用GetCurrentBuffer获取图片大小出错，通过调试发现是因为Filter Graph的状态不对，MSDN中说调用GetCurrentBuffer方法的时候“Do not call this method while the filter graph is running.”。那我应该何时调用呢？在Run后调用Stop和Pause方法都不行，调用IMediaEvent::GetEvent方法测试，使用以下代码：

while (hr = pEvent->GetEvent(&evCode, ¶m1, ¶m2, 0), SUCCEEDED(hr))
{
    //add the evCode to a int array[]
}

发现一共返回了5个evCode，从array[0] --array[4]分别是：EC_PALETTE_CHANGED，EC_VIDEO_SIZE_CHANGED，EC_CLOCK_CHANGED，EC_PAUSED，EC_PAUSED
然后调用GetCurrentBuffer依然出错

难道除了Sleep就没有别的方法了么？
SetBufferSamples( TRUE )之后DirectShow到底做了什么？对Filter Graph有什么影响？如何知道何时调用GetCurrentBuffer？有没有详细的资料？

附代码：

HRESULT DSComment::CreatFilterGraph(){
		
		HRESULT hr;
		cli::pin_ptr<IGraphBuilder *> ppGraphManager = &pGraphManager;
		cli::pin_ptr<ICaptureGraphBuilder2 *> ppCapture = &pCapture;
		
		if(!ppGraphManager || !ppCapture){
			return E_POINTER;
		}
		
		hr = CoCreateInstance (
			CLSID_FilterGraph, 
			NULL,
			CLSCTX_INPROC_SERVER,   //for add grephedit
            IID_IGraphBuilder, 
			(void **) ppGraphManager
			);
		if (FAILED(hr)){
			MessageBox::Show("Initial IFilterGraph2 failed!");
			return E_NOINTERFACE;
		}	
		


		// Create the capture graph builder
		 hr = CoCreateInstance (
			 CLSID_CaptureGraphBuilder2, 
			 NULL, 
			 CLSCTX_INPROC_SERVER,
             IID_ICaptureGraphBuilder2, 
			 (void **) ppCapture
			 );
		 if (FAILED(hr)){
			 MessageBox::Show("Initial ICaptureGraphBuilder2 failed!");
			 return E_NOINTERFACE;
		 }		 
		return S_OK;
	}

	
	HRESULT DSComment::CreatGrabberFilter(){
		
		HRESULT hr;
		cli::pin_ptr<IBaseFilter *> ppGrabberBaseFilter = &pGrabberBaseFilter;
		
		hr = CoCreateInstance(
			CLSID_SampleGrabber, 
			NULL, 
			CLSCTX_INPROC_SERVER,
			IID_IBaseFilter, 
			(void**)ppGrabberBaseFilter
			);
		

		if (FAILED(hr))
		{
			MessageBox::Show("Couldn't create sample grabber filter base!");
			return E_NOINTERFACE;
		} 
		

		cli::pin_ptr<ISampleGrabber *> ppGrabber = &pGrabber;
		
		pGrabberBaseFilter->QueryInterface(IID_ISampleGrabber, (void**)ppGrabber);
		
		AM_MEDIA_TYPE mt;
		ZeroMemory(&mt, sizeof(AM_MEDIA_TYPE));
		mt.majortype = MEDIATYPE_Video;
		mt.subtype = MEDIASUBTYPE_RGB24;
		hr = pGrabber->SetMediaType(&mt);
		FreeMediaType(mt);

		return hr;
	}

	
	HRESULT DSComment::CreatCaptureFilter(){
	    
		HRESULT hr;
		ULONG cFetched;
		const char* CAPTUREDEVNAME;
		
		CAPTUREDEVNAME = "USB 视频设备";


		cli::pin_ptr<IBaseFilter *> ppCaptureBaseFilter = &pCaptureBaseFilter;
	   
		// Create the system device enumerator
		ICreateDevEnum *pDevEnum =NULL;
		
		hr = CoCreateInstance (
			CLSID_SystemDeviceEnum, 
			NULL, 
			CLSCTX_INPROC,
			IID_ICreateDevEnum, 
			(void **) &pDevEnum
			);
		if (FAILED(hr)){
			MessageBox::Show("Couldn't create system enumerator!");
			return E_NOINTERFACE;
		}

		// Create an enumerator for the video capture devices
		IEnumMoniker *pClassEnum = NULL;

		hr = pDevEnum->CreateClassEnumerator(
			CLSID_VideoInputDeviceCategory, 
			&pClassEnum, 
			0
			);

		if (FAILED(hr)){
			MessageBox::Show("Couldn't create class enumerator!");
			return E_NOINTERFACE;
		}

		// If there are no enumerators for the requested type, then 
		// CreateClassEnumerator will succeed, but pClassEnum will be NULL.
		if (pClassEnum == NULL){
			MessageBox::Show("No video capture device was detected.\r\n\r\n	  \
					This sample requires a video capture device, such as a USB WebCam,\r\n \
					to be installed and working properly.  The sample will now close. \
					No Video Capture Hardware");
			return E_FAIL;
		}

		IMoniker *pMoniker = NULL;

		// Use the first video capture device on the device list.
		// Note that if the Next() call succeeds but there are no monikers,
		// it will return S_FALSE (which is not a failure).  Therefore, we
		// check that the return code is S_OK instead of using SUCCEEDED() macro.
		if (S_OK == (pClassEnum->Next (1, &pMoniker, &cFetched))){

			// Bind Moniker to a filter object
			hr = pMoniker->BindToObject(0,0,IID_IBaseFilter, (void**)ppCaptureBaseFilter);
			
			IPropertyBag *pPropBag = NULL;
			hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag, (void **)&pPropBag);
			if (FAILED(hr)){
				pMoniker->Release();
				return E_NOINTERFACE;  
			} 
			
			VARIANT var;
			VariantInit(&var);

			// Get description or friendly name.
			hr = pPropBag->Read(L"Description", &var, 0);
			if (FAILED(hr)){
				hr = pPropBag->Read(L"FriendlyName", &var, 0);
			}

			if (SUCCEEDED(hr)){
				String^ strCaptureDevName = String(var.bstrVal).ToString();
				if(!strCaptureDevName->CompareTo(String(CAPTUREDEVNAME).ToString())){
					hr = S_OK;
				}else{
					hr = E_FAIL;
					return hr;
				}
			}
			pPropBag->Release();
		}else{
			MessageBox::Show("Unable to access video capture device!");   
			return E_FAIL;
		}

		
		pMoniker->Release();
		pClassEnum->Release();
		pDevEnum->Release();
		return hr;

	}

	

	HRESULT DSComment::BuiltFilterGraph(){
		
		HRESULT hr;
		pGraphManager->AddFilter(pCaptureBaseFilter, L"Capture Device");
		pGraphManager->AddFilter(pGrabberBaseFilter, L"Sample Grabber Filter");

		pCapture->SetFiltergraph(pGraphManager);

		pCapture->RenderStream(
			&PIN_CATEGORY_PREVIEW,
			 &MEDIATYPE_Video,
			 pCaptureBaseFilter,
			 pGrabberBaseFilter,
			 NULL
			 
			);

		
		cli::pin_ptr<IVideoWindow *> ppVW = &pVW;
		cli::pin_ptr<IMediaControl *> ppMC = &pMC;
		cli::pin_ptr<IMediaEventEx *> ppME = &pME;

		hr = pGraphManager->QueryInterface(IID_IMediaControl,(LPVOID *) ppMC);
		 if (FAILED(hr)){
			MessageBox::Show("Initial IMediaControl failed!");
			return E_NOINTERFACE;
		 }
		 	 
		 hr = pGraphManager->QueryInterface(IID_IMediaEvent, (LPVOID *) ppME);
		 if (FAILED(hr)){
			MessageBox::Show("Initial IMediaEventEx failed!");
			return E_NOINTERFACE;
		 }
		 
		 hr = pGraphManager->QueryInterface(IID_IVideoWindow, (LPVOID *) ppVW);
		 if (FAILED(hr)){
			MessageBox::Show("Initial IVideoWindow failed!");
			return E_NOINTERFACE;
		 }	

	}

BYTE* DSComment::SnapStillImage(long* size){
		
		HRESULT hr;

		pMC->Stop();

		hr = pGrabber->SetBufferSamples( TRUE );

			// Only grab one at a time, stop stream after
			// grabbing one sample
			//
		hr = pGrabber->SetOneShot( FALSE );

		pMC->Run();


                //××××××××××××××××××××××××××××××××××××××××××××××××××××××××
		//就是在这里除了Sleep难道没有别的方法可以保证GetCurrentBuffer成功？？
               //×××××××××××××××××××××××××××××××××××××××××××××××××××××××××××

		long cbBuffer;
		hr = pGrabber->GetCurrentBuffer(&cbBuffer, NULL);
		if (FAILED(hr))
		{
			MessageBox::Show("GetCurrentBuffer Fail!");	
		}

		BYTE *pBuffer = (BYTE*)CoTaskMemAlloc(cbBuffer);
		if (!pBuffer) 
		{
			MessageBox::Show("CoTaskMemAlloc Fail!");
		}

		hr = pGrabber->GetCurrentBuffer(&cbBuffer, (long*)pBuffer);
		if (FAILED(hr))
		{
			MessageBox::Show("GetCurrentBuffer Fail!");
			
		}
		
		hr = pGrabber->SetOneShot( FALSE );

		AM_MEDIA_TYPE mt;

		hr = pGrabber->GetConnectedMediaType(&mt);
		if (FAILED(hr))
		{
			MessageBox::Show("GetConnectedMediaType Fail!");
			
		}

		VIDEOINFOHEADER *pVih = (VIDEOINFOHEADER*)mt.pbFormat;

		long cbBMI = mt.cbFormat - SIZE_PREHEADER;

		long captureSize = cbBMI + cbBuffer + sizeof(BITMAPFILEHEADER);
		*size = captureSize;
		BYTE *pCaptrue = (BYTE*)CoTaskMemAlloc(captureSize);

		BITMAPFILEHEADER bmf = { };
		

		bmf.bfType = 'MB';
		bmf.bfSize = captureSize; 
		bmf.bfOffBits = sizeof(bmf) + cbBMI; 

		memcpy(pCaptrue, &bmf, sizeof(bmf));
		
		memcpy((pCaptrue + sizeof(bmf)), &pVih->bmiHeader, cbBMI);
		memcpy((pCaptrue + sizeof(bmf) + cbBMI), pBuffer, cbBuffer);
	
		return pCaptrue;		

	}

[mf1983]

多谢Huntercao的指教 其实我刚开始的时候也加过NullRenderer，但是我觉得后面这个Render类型不是最重要的。 在上面的代码中我用系统自动添加的video render，设置

SetBufferSamples( TRUE ) ;
SetOneShot( TRUE )

也能抓图，只是预览视频的功能停止了。看MSDN上说setoneshot后会给后面的render发一个IPin::endstream（可能不准确，大意是告诉后面的render没有vidoe stream了），这个能否通过操作IPin继续恢复视频预览的功能？ 对于GetCurrentBuffer，是不是除了sleep，只能配合setoneshot（TRUE），然后设置IMediaControl::waitforcomple（INFINITE, &EvCode）来完成sample的buffer？不能通过IMediaEvent::getevente或IMediaControl::getstate的方法获得么？ 我现在最想知道的是GetCurrentBuffer这条路是否能走的通，实在不行就转callback了，之前也尝试过callback模式，有点问题没有继续深入～～～ 再次感此Huntercao的指教

[曹大夯]

一般情况下，Sample Grabber是用ISampleGrabber::SetCallback method 来获取Snap Image Buffer的。 例子提供的Graph，其Render是Null的，不需要实际显示视频；而你的应用程序，Render不是Null Render，所以应该用Call Back，在CallBack里面获取图像。

[曹大夯]

用回调函数，在回调函数里面读取Image Buffer是不会影响视频Preview的，除非你在回调函数里面做太多事，有可能影响视频的流畅性。

[mf1983]

好的，多谢指教，我再研究下