Previewing Video using DirectShow

用摄像头预览过程如下：

ICaptureGraphBuilder2 *pBuild; // Capture Graph Builder
// Initialize pBuild (not shown).

IBaseFilter *pCap; // Video capture filter.
/* Initialize pCap and add it to the filter graph (not shown). */

hr = pBuild->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, 
    pCap, NULL, NULL);

其中pBuild 初始化如下：

HRESULT InitCaptureGraphBuilder(
  IGraphBuilder **ppGraph,  // Receives the pointer.
  ICaptureGraphBuilder2 **ppBuild  // Receives the pointer.
)
{
    if (!ppGraph || !ppBuild)
    {
        return E_POINTER;
    }
    IGraphBuilder *pGraph = NULL;
    ICaptureGraphBuilder2 *pBuild = NULL;

    // Create the Capture Graph Builder.
    HRESULT hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, 
        CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2, (void**)&pBuild );
    if (SUCCEEDED(hr))
    {
        // Create the Filter Graph Manager.
        hr = CoCreateInstance(CLSID_FilterGraph, 0, CLSCTX_INPROC_SERVER,
            IID_IGraphBuilder, (void**)&pGraph);
        if (SUCCEEDED(hr))
        {
            // Initialize the Capture Graph Builder.
            pBuild->SetFiltergraph(pGraph);

            // Return both interface pointers to the caller.
            *ppBuild = pBuild;
            *ppGraph = pGraph; // The caller must release both interfaces.
            return S_OK;
        }
        else
        {
            pBuild->Release();
        }
    }
    return hr; // Failed
}

pCap初始化，通过实例化一个capture filter，然后加入到graph链路。
枚举视频捕获设备如下：

ICreateDevEnum *pDevEnum = NULL;
IEnumMoniker *pEnum = NULL;

// Create the System Device Enumerator.
HRESULT hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL,
    CLSCTX_INPROC_SERVER, IID_ICreateDevEnum, 
    reinterpret_cast<void**>(&pDevEnum));
if (SUCCEEDED(hr))
{
    // Create an enumerator for the video capture category.
    hr = pDevEnum->CreateClassEnumerator(
        CLSID_VideoInputDeviceCategory,
        &pEnum, 0);
}

显示设备信息如下：

HWND hList; // Handle to the list box.
IMoniker *pMoniker = NULL;
while (pEnum->Next(1, &pMoniker, NULL) == S_OK)
{
    IPropertyBag *pPropBag;
    hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag, 
        (void**)(&pPropBag));
    if (FAILED(hr))
    {
        pMoniker->Release();
        continue;  // Skip this one, maybe the next one will work.
    } 
    // Find the description or friendly name.
    VARIANT varName;
    VariantInit(&varName);
    hr = pPropBag->Read(L"Description", &varName, 0);
    if (FAILED(hr))
    {
        hr = pPropBag->Read(L"FriendlyName", &varName, 0);
    }
    if (SUCCEEDED(hr))
    {
        // Add it to the application's list box.
        USES_CONVERSION;
        (long)SendMessage(hList, LB_ADDSTRING, 0, 
            (LPARAM)OLE2T(varName.bstrVal));
        VariantClear(&varName); 
    }
    pPropBag->Release();
    pMoniker->Release();
}

加入到链路：

IBaseFilter *pCap = NULL;
hr = pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pCap);
if (SUCCEEDED(hr))
{
    hr = m_pGraph->AddFilter(pCap, L"Capture Filter");
}

以上过程来自directshow帮助文档，整理后代码如下：

HRESULT InitCaptureGraphBuilder(
	IGraphBuilder **ppGraph,  // Receives the pointer.
	ICaptureGraphBuilder2 **ppBuild  // Receives the pointer.
	)
{
	if (!ppGraph || !ppBuild)
	{
		return E_POINTER;
	}
	IGraphBuilder *pGraph = NULL;
	ICaptureGraphBuilder2 *pBuild = NULL;

	// Create the Capture Graph Builder.
	HRESULT hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, 
		CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2, (void**)&pBuild );
	if (SUCCEEDED(hr))
	{
		// Create the Filter Graph Manager.
		hr = CoCreateInstance(CLSID_FilterGraph, 0, CLSCTX_INPROC_SERVER,
			IID_IGraphBuilder, (void**)&pGraph);
		if (SUCCEEDED(hr))
		{
			// Initialize the Capture Graph Builder.
			pBuild->SetFiltergraph(pGraph);

			// Return both interface pointers to the caller.
			*ppBuild = pBuild;
			*ppGraph = pGraph; // The caller must release both interfaces.
			return S_OK;
		}
		else
		{
			pBuild->Release();
		}
	}
	return hr; // Failed
}



HRESULT EnumerateDevices(REFGUID category, IEnumMoniker **ppEnum)
{
	ICreateDevEnum *pDevEnum = NULL;

	// Create the System Device Enumerator.
	HRESULT hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL,
		CLSCTX_INPROC_SERVER, IID_ICreateDevEnum, 
		reinterpret_cast<void**>(&pDevEnum));
	if (SUCCEEDED(hr))
	{
		// Create an enumerator for the video capture category.
		hr = pDevEnum->CreateClassEnumerator(
			CLSID_VideoInputDeviceCategory,
			ppEnum, 0);
	}
	return hr;
}
void DisplayDeviceInformation(IEnumMoniker *pEnum, IMoniker** pMoniker)
{
	HWND hList; // Handle to the list box.
	while (pEnum->Next(1, pMoniker, NULL) == S_OK)
	{
		IPropertyBag *pPropBag;
		HRESULT hr = (*pMoniker)->BindToStorage(0, 0, IID_IPropertyBag, 
			(void**)(&pPropBag));
		if (FAILED(hr))
		{
			(*pMoniker)->Release();
			continue;  // Skip this one, maybe the next one will work.
		} 
		// Find the description or friendly name.
		VARIANT varName;
		VariantInit(&varName);
		hr = pPropBag->Read(L"Description", &varName, 0);
		if (FAILED(hr))
		{
			hr = pPropBag->Read(L"FriendlyName", &varName, 0);
		}
		if (SUCCEEDED(hr))
		{
			// Add it to the application's list box.
			USES_CONVERSION;
			/*(long)SendMessage(hList, LB_ADDSTRING, 0, 
			(LPARAM)OLE2T(varName.bstrVal));*/
			VariantClear(&varName); 
		}
		pPropBag->Release();
		(*pMoniker)->Release();
	}


}

调用代码：

ICaptureGraphBuilder2 *pBuild;
IGraphBuilder *ppGraph;
IMoniker* pMoniker;
IMediaControl *pControl;
IMediaEvent   *pEvent;
InitCaptureGraphBuilder(&ppGraph,&pBuild);
hr = ppGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
hr = ppGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
IBaseFilter *pCap; // Video capture filter.
IEnumMoniker *pEnum;

hr = EnumerateDevices(CLSID_VideoInputDeviceCategory, &pEnum);
			
DisplayDeviceInformation(pEnum, &pMoniker);
hr = pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pCap);
if (SUCCEEDED(hr))
	{
		hr = ppGraph->AddFilter(pCap, L"Capture Filter");
	}
hr = pBuild->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, pCap, NULL, NULL);
hr = pControl->Run();

运行获得filter的连接情况：

接下就是把捕获的视频进行保存了

IBaseFilter *pMux;
hr = pBuild->SetOutputFileName(&MEDIASUBTYPE_Avi,L"D:\\Example.avi",&pMux,NULL);
hr = pBuild->RenderStream(&PIN_CATEGORY_CAPTURE,&MEDIATYPE_Video,pCap,NULL,pMux);

程序调试了很久，刚开始链路是正确的，但是没办法播放，原因是存放地址放在了C盘，可能是win7 系统权限问题，修改保存路径到D盘就可以了。

如果需要对文件先进行编码，然后保存，代码如下：

Specify the encoder filter as the fourth parameter to RenderStream, shown in bold in the following example:

IBaseFilter *pEncoder;
/* Create the encoder filter (not shown). */
// Add it to the filter graph.
pGraph->AddFilter(pEncoder, L"Encoder);

/* Call SetOutputFileName as shown previously. */

// Render the stream.
hr = pBuild->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, 
    pCap, pEncoder, pMux);
pEncoder->Release();