windows directshow使用lav filter开发h264码流摄像头（2）

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前言

之前发布过一篇文章 windows directshow使用lav filter开发h264码流摄像头
，但是存在一个问题就是 预览的延时太大。因为 Video Mixing Renderer 9 是比较老的呈现器，无法使用 lav filter 的硬件加速，需要将呈现器更换成 Enhanced Video Renderer(EVR) 呈现器才可以使用硬件加速，但两个呈现器的使用方法有所差别，于是就有了这篇文章。
这篇文章主要实现以下三个功能：

1. 使用硬件加速降低h264摄像头预览延迟
2. 预览实时码流显示
3. 预览视频录制

先提供实际效果图和graphedt的调试图流程：



注意 lav filter 框起来的地方要正确显示激活硬件加速，才可以降低预览的延时。

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功能开发

对于开发环境，开发流程和技巧在 windows directshow使用lav filter开发h264码流摄像头
有详细的说明，这篇文章主要是对新增功能展开讨论。

一、降低预览延迟

这里要做的主要是将 Video Mixing Renderer 9 呈现器更换成 Enhanced Video Renderer(EVR) 呈现器。两者用法不一样，主要表现在设置呈现窗口句柄、位图等…

/*
* funtion: GetUnconnectedPin
* 获取filter未连接的Pin口
*/
IPin* GetUnconnectedPin(IBaseFilter* pFilter, PIN_DIRECTION PinDir) {
    IEnumPins* pEnumPins = NULL;
    IPin* pPin = NULL;

    pFilter->EnumPins(&pEnumPins);
    while (pEnumPins->Next(1, &pPin, NULL) == S_OK) {
        PIN_INFO pinInfo;
        pPin->QueryPinInfo(&pinInfo);

        if (pinInfo.pFilter) {
            pinInfo.pFilter->Release(); // 释放资源
        }

        // 检查 pin 方向是否匹配
        if (pinInfo.dir == PinDir) {
            IPin* pTmp = NULL;
            // 检查是否未连接
            if (pPin->ConnectedTo(&pTmp) != S_OK) {
                // 找到未连接的 pin
                pEnumPins->Release();
                return pPin;
            }
            pTmp->Release();
        }
        pPin->Release();
    }
    pEnumPins->Release();
    return NULL;
}

HRESULT hr;

IGraphBuilder* pGraphBuilder;
hr = CoCreateInstance(CLSID_FilterGraph, nullptr, CLSCTX_INPROC_SERVER,
                      IID_IGraphBuilder, (void **)&pGraphBuilder);

//创建EVR呈现器实例
IBaseFilter* pEvrFilter;
hr = CoCreateInstance(CLSID_EnhancedVideoRenderer, nullptr, CLSCTX_INPROC_SERVER,
                      IID_IBaseFilter, (void **) &pEvrFilter);
hr = pGraphBuilder->AddFilter(pEvrFilter, L"EVR Filter");

//连接lav filter和EVR呈现器
pGraphBuilder->ConnectDirect(GetUnconnectedPin(m_pLavVideoFilter, PINDIR_OUTPUT), GetUnconnectedPin(m_pMixingFilter, PINDIR_INPUT), nullptr); 

//获取设置窗口句柄的接口和设置位图的接口
IMFGetService* pService = NULL;
IMFVideoDisplayControl* pVideoDisplayCtl;
IMFVideoMixerBitmap* pBMP;

hr = m_pMixingFilter->QueryInterface(IID_IMFGetService, (LPVOID *) &pService);
if (SUCCEEDED(hr)) {
    hr = pService->GetService(MR_VIDEO_RENDER_SERVICE, IID_IMFVideoDisplayControl, (void**)&pVideoDisplayCtl);
    if (SUCCEEDED(hr)) {
        // 设置视频窗口句柄
        hr = m_pVideoDisplayCtl->SetVideoWindow((HWND)effectiveWinId());
    } else {
        std::cout << "query video display control failed, hr = " << hr;
        pService->Release();
        return false;
    }
    hr = pService->GetService(MR_VIDEO_MIXER_SERVICE, IID_IMFVideoMixerBitmap, (void**)&pBMP);
    if (FAILED(hr)) {
        std::cout << "query video display control failed, hr = " << hr;
        pService->Release();
        return false;
    }
    pService->Release();
} else {
    std::cout << "query IMF Service failed, hr = " << hr;
    return false;
}

二、显示预览实时码率

实时码率无法通过接口直接获取，主要是通过重载 SampleCB(double, IMediaSample*) 函数，获取数据大小，通过码率的计算公式计算后得到。这里通过位图实时显示，就顺便提供 EVR呈现器 位图的使用方法（与Video Mixing Renderer 9不一样）。

int updateMarker( std::vector<std::wstring> qslPrama, float t=0.0f, float b=0.2f, float l=0.0f, float r=0.3f )
{
    LONG hr;
    HWND hwndApp = (HWND)winId();
    const TCHAR *szNewText = reinterpret_cast<const wchar_t *>(qslPrama.first().c_str());

    HDC hdc = GetDC(hwndApp);
    HDC hdcBmp = CreateCompatibleDC(hdc);

    int nLength, nTextBmpWidth, nTextBmpHeight;
    SIZE sz={0};
    nLength = (int) _tcslen(szNewText);
    GetTextExtentPoint32(hdcBmp, szNewText, nLength, &sz);
    nTextBmpHeight = sz.cy;
    nTextBmpWidth  = sz.cx;

    HBITMAP hbm = CreateCompatibleBitmap(hdc, nTextBmpWidth, nTextBmpHeight*qslPrama.size());
    ReleaseDC(hwndApp, hdc);

    HBITMAP hbmOld = (HBITMAP)SelectObject(hdcBmp, hbm);

    RECT rcText;
    SetRect(&rcText, 0, 0, nTextBmpWidth, nTextBmpHeight*qslPrama.size());
    SetBkColor(hdcBmp, RGB(0, 0, 0));
    SetTextColor(hdcBmp, RGB(0, 255, 0));
    for( int i = 0; i < qslPrama.size(); i++ ) {
        szNewText = reinterpret_cast<const wchar_t *>(qslPrama.at(i).c_str());
        nLength = (int) _tcslen(szNewText);
        TextOut(hdcBmp, 0, nTextBmpHeight*i, szNewText, nLength);
    }

    // 准备位图信息
    MFVideoAlphaBitmap ab;
    ZeroMemory(&ab, sizeof(ab));
    ab.GetBitmapFromDC = TRUE;
    ab.params.dwFlags = VMRBITMAP_HDC;
    ab.bitmap.hdc = hdcBmp;

    // 设置位图显示的位置和大小（归一化坐标：0.0 - 1.0）
    MFVideoNormalizedRect nrcDest = { l, t, r, b };
    ab.params.nrcDest = nrcDest;
    ab.params.rcSrc = rcText;

    ab.params.fAlpha = 0.6f;  // 设置透明度 (0.0-1.0)
    ab.params.clrSrcKey = RGB(255, 255, 255);
    ab.params.dwFlags |= MFVideoAlphaBitmap_SrcColorKey;
    ab.params.dwFlags |= MFVideoAlphaBitmap_Alpha;
    ab.params.dwFlags |= MFVideoAlphaBitmap_DestRect;

    hr = m_pBMP->SetAlphaBitmap(&ab);
    if (FAILED(hr))
        std::cout << "SetAlphaBitmap FAILED!  hr=" << hr;

    DeleteObject(SelectObject(hdcBmp, hbmOld));

    DeleteObject(hbm);
    DeleteDC(hdcBmp);

    return hr;
}

//重载的函数回调频率是根据帧率来决定的，根据实际情况控制码率计算
//继承ISampleGrabberCB后重载函数
class CSampleGrabberCB : public ISampleGrabberCB {
int m_u8CallCounts{0};
int m_u16SecSize{0};
int m_u8fps{15};

public:
    STDMETHODIMP SampleCB(double SampleTime, IMediaSample *pSample) {
        long size = pSample->GetActualDataLength();  // 获取帧的大小（字节）

	    if(m_u8CallCounts == m_u8fps) {
	        double bitrate = (double)m_u16SecSize*8/1000;
	        m_u16SecSize = 0;
	        m_u8CallCounts = 0;
	        std::vector<std::wstring> qslPrama;
	        qslPrama.push_back(L"码率: "+std::to_string(bitrate)+L"/kbps");
	        updateMarker(qslPrama);
	    } else {
	        m_u16SecSize += size;
	        m_u8CallCounts++;
	    }
		
	    return S_OK;
	}
};

//设置我们继承的类
ISampleGrabber* pSampleGrabber;
IBaseFilter* pGrabberFilter;

hr = CoCreateInstance(CLSID_SampleGrabber, nullptr, CLSCTX_INPROC_SERVER,
          			  IID_ISampleGrabber, (void **)&pSampleGrabber);
hr = pSampleGrabber->QueryInterface(IID_IBaseFilter, (void **)&pGrabberFilter);
hr = pGraphBuilder->AddFilter(pGrabberFilter, L"Sample Grabber");

pGraphBuilder->ConnectDirect(GetUnconnectedPin(pVideoCaptureFilter, PINDIR_OUTPUT), GetUnconnectedPin(pTeeFilter, PINDIR_INPUT), nullptr);
pGraphBuilder->ConnectDirect(GetUnconnectedPin(pTeeFilter, PINDIR_OUTPUT), GetUnconnectedPin(pGrabberFilter, PINDIR_INPUT), nullptr);
pGraphBuilder->ConnectDirect(GetUnconnectedPin(pGrabberFilter, PINDIR_OUTPUT), GetUnconnectedPin(m_pLavVideoFilter, PINDIR_INPUT), nullptr);

CSampleGrabberCB* pSampleGrabberCB = new CSampleGrabberCB();
pSampleGrabber->SetCallback(pSampleGrabberCB, 0);

三、预览视频录制

这个很简单直接给代码，如果需要输出mp4格式，需要下载一个 GDCL Mpeg-4 filter。这里给出网址 https://www.gdcl.co.uk/mpeg4/。
如果是保存avi格式，直接使用自带的 AVI Mux 就可以了。

IBaseFilter* pWriter;
IBaseFilter* pMp4Mux;

hr = CoCreateInstance(CLSID_FileWriter, nullptr, CLSCTX_INPROC_SERVER, IID_IBaseFilter, (void**)&pWriter);
hr = CoCreateInstance(CLSID_GDCLMp4Mux, nullptr, CLSCTX_INPROC_SERVER, IID_IBaseFilter, (void**)&pMp4Mux);
//设置输出文件路径
IFileSinkFilter *pFileSink = nullptr;
pWriter->QueryInterface(IID_IFileSinkFilter, (void**)&pFileSink);
std::wstring outFileName = L"out.mp4";
hr = pFileSink->SetFileName(outFileName.c_str(), nullptr);

hr = pGraphBuilder->AddFilter(pMp4Mux, L"GDCL Mp4 Mux");
hr = pGraphBuilder->AddFilter(pWriter, L"File Writer");

//按照graphedt图连接
pGraphBuilder->ConnectDirect(GetUnconnectedPin(pVideoCaptureFilter, PINDIR_OUTPUT), GetUnconnectedPin(pTeeFilter, PINDIR_INPUT), nullptr);
pGraphBuilder->ConnectDirect(GetUnconnectedPin(pTeeFilter, PINDIR_OUTPUT), GetUnconnectedPin(pGrabberFilter, PINDIR_INPUT), nullptr);
pGraphBuilder->ConnectDirect(GetUnconnectedPin(pGrabberFilter, PINDIR_OUTPUT), GetUnconnectedPin(m_pLavVideoFilter, PINDIR_INPUT), nullptr);
pGraphBuilder->ConnectDirect(GetUnconnectedPin(m_pLavVideoFilter, PINDIR_OUTPUT), GetUnconnectedPin(m_pMixingFilter, PINDIR_INPUT), nullptr);
pGraphBuilder->ConnectDirect(GetUnconnectedPin(pTeeFilter, PINDIR_OUTPUT), GetUnconnectedPin(pMp4Mux, PINDIR_INPUT), nullptr);
pGraphBuilder->ConnectDirect(GetUnconnectedPin(pMp4Mux, PINDIR_OUTPUT), GetUnconnectedPin(pWriter, PINDIR_INPUT), nullptr);

代码是节选出来的，可能无法直接运行。