如何在DShow采集中使用VMR-9做预览

DShow默认的预览窗口（IVideoWindow）对绘制的控制太弱了，想自己在上面叠加文字线条什么的几乎不可能。使用VMR-7或者VMR-9显示的控制要方便很多。

#include <d3d9.h>
#include <Vmr9.h>

    // Create the VMR-9:
    hr = CoCreateInstance(CLSID_VideoMixingRenderer9, 0,
        CLSCTX_INPROC_SERVER, IID_IBaseFilter, (void**)&m_pVmr9);
    if (FAILED(hr))
    {
        return FALSE;
    }

    // Add the VMR-9 to the filter graph:
    hr = m_pGraphBuilder->AddFilter(m_pVmr9, L"VMR9");
    if (FAILED(hr))
        return FALSE;

    // Set video window style and position
    hr = SetupVideoWindow();
    if (FAILED(hr))
        return FALSE;

    // Render the preview pin on the video capture filter
    // Use this instead of m_pGraph->RenderFile
    hr = m_pCapture->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video,
        m_pSrcFilter, NULL, m_pVmr9);
    if (FAILED(hr))
    {
        SAFE_RELEASE(m_pSrcFilter);
        return FALSE;
    }


HRESULT CDShowDevStream::SetupVideoWindow()
{
    HRESULT hr;
    HWND hwnd;
    IVMRWindowlessControl* pWc = NULL;
    // Set the rendering mode and number of streams.  
    IVMRFilterConfig *pConfig;

    hr = m_pVmr9->QueryInterface(IID_IVMRFilterConfig9, (void**)&pConfig);
    if (SUCCEEDED(hr))
    {
        pConfig->SetRenderingMode(VMRMode_Windowless);
        pConfig->Release();
    }

    hwnd = (HWND)param_.window.info.win.hwnd;
    // Set the video window to be a child of the main window
    hr = m_pVmr9->QueryInterface(IID_IVMRWindowlessControl9, (void**)&m_pVmrWc);
    if (SUCCEEDED(hr))
    {
        m_pVmrWc->SetVideoClippingWindow(hwnd);
    }
    else
        return hr;

    // Find the native video size.
    long lWidth, lHeight;
    HRESULT hr = m_pVmrWc->GetNativeVideoSize(&lWidth, &lHeight, NULL, NULL);
    if (SUCCEEDED(hr))
    {
        RECT rcSrc, rcDest;
        // Set the source rectangle.
        SetRect(&rcSrc, 0, 0, lWidth, lHeight);

        // Get the window client area.
        GetClientRect(hwnd, &rcDest);
        // Set the destination rectangle.
        SetRect(&rcDest, 0, 0, rcDest.right, rcDest.bottom);

        // Set the video position.
        hr = m_pVmrWc->SetVideoPosition(&rcSrc, &rcDest);
    }

    return hr;
}

MSDN上面的主要参考资料
https://msdn.microsoft.com/en-us/library/ms779725(v=VS.85).ASPx
https://msdn.microsoft.com/en-us/library/ms787876.aspx