Windows平臺(tái)使用DirectShow獲取UVC攝像頭上按鍵后的抓拍圖

什么是UVC攝像頭，UVC是什么意思？

UVC是一種標(biāo)準(zhǔn)的USB視頻設(shè)備協(xié)議，就是傳說(shuō)中的免驅(qū)攝像頭。UVC是Usb Video Class的簡(jiǎn)稱(chēng)。
Windows平臺(tái)上UVC驅(qū)動(dòng)文檔

DirectShow簡(jiǎn)介

DirectShow是微軟公司在ActiveMovie和Video for Windows的基礎(chǔ)上推出的新一代基于COM(Component Object Model)的流媒體處理的開(kāi)發(fā)包，與DirectX開(kāi)發(fā)包一起發(fā)布。DirectShow使用一種叫Filter Graph的模型來(lái)管理整個(gè)數(shù)據(jù)流的處理過(guò)程，運(yùn)用DirectShow，我們可以很方便地從支持WDM驅(qū)動(dòng)模型的采集卡上捕獲數(shù)據(jù)，并且進(jìn)行相應(yīng)的后期處理乃至存儲(chǔ)到文件中。這樣使在多媒體數(shù)據(jù)庫(kù)管理系統(tǒng)（MDBMS）中多媒體數(shù)據(jù)的存取變得更加方便。它廣泛地支持各種媒體格式，包括Asf、Mpeg、Avi、Dv、Mp3、Wave等，為多媒體流的捕捉和回放提供了強(qiáng)有力的支持。

調(diào)用DirectShow獲取攝像頭按鍵后的抓拍圖片

MSDN文檔：Video Capture

Filter

DirectShow使用模塊化體系結(jié)構(gòu)，其中每個(gè)處理階段都由稱(chēng)為filter的COM對(duì)象完成。 DirectShow為應(yīng)用程序提供了一組標(biāo)準(zhǔn)filter，開(kāi)發(fā)人員可以編寫(xiě)自己的自定義過(guò)濾器來(lái)擴(kuò)展DirectShow的功能。

Graph

有多個(gè)Filter連接，構(gòu)成Graph。Filter Graph Manager用來(lái)構(gòu)建和控制Graph中的Filter

代碼實(shí)戰(zhàn)

初始化各個(gè)Com接口

HRESULT GetInterfaces(void)
{
    HRESULT hr;

    //創(chuàng)建Filter Graph Manager.
    hr = CoCreateInstance (CLSID_FilterGraph, NULL, CLSCTX_INPROC,
        IID_IGraphBuilder, (void **) &pGraphBuilder);
    if (FAILED(hr))
        return hr;
    //創(chuàng)建Capture Graph Builder.
    hr = CoCreateInstance (CLSID_CaptureGraphBuilder2 , NULL, CLSCTX_INPROC,
        IID_ICaptureGraphBuilder2, (void **) &pCaptureGraphBuilder2);
    if (FAILED(hr))
        return hr;

    // IMediaControl接口，用來(lái)控制流媒體在Filter Graph中的流動(dòng)，例如流媒體的啟動(dòng)和停止；
    hr = pGraphBuilder->QueryInterface(IID_IMediaControl,(LPVOID *) &pMediaControl);
    if (FAILED(hr))
        return hr;

    // IVideoWindow,用來(lái)顯示預(yù)覽視頻
    hr = pGraphBuilder->QueryInterface(IID_IVideoWindow, (LPVOID *) &pVideoWindow);
    if (FAILED(hr))
        return hr;

    // IMediaEvent接口，該接口在Filter Graph發(fā)生一些事件時(shí)用來(lái)創(chuàng)建事件的標(biāo)志信息并傳送給應(yīng)用程序
    hr = pGraphBuilder->QueryInterface(IID_IMediaEvent,(LPVOID *) &pMediaEvent);
    if (FAILED(hr))
        return hr;

    //創(chuàng)建用于預(yù)覽的Sample Grabber Filter.
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER,
        IID_IBaseFilter, (void**)&pGrabberF);
    if (FAILED(hr))
        return hr;

    //獲取ISampleGrabber接口，用于設(shè)置回調(diào)等相關(guān)信息
    hr = pGrabberF->QueryInterface(IID_ISampleGrabber, (void**)&pSampleGrabber);
    if (FAILED(hr)) 
        return hr;

    //創(chuàng)建用于抓拍的Sample Grabber Filter.
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER,IID_IBaseFilter, (void**)&pGrabberStill);
    if (FAILED(hr))
        return hr;

    //獲取ISampleGrabber接口，用于設(shè)置回調(diào)等相關(guān)信息
    hr = pGrabberStill->QueryInterface(IID_ISampleGrabber, (void**)&pSampleGrabberStill);
    if (FAILED(hr)) 
        return hr;

    //創(chuàng)建Null Filter
    hr = CoCreateInstance(CLSID_NullRenderer,NULL,CLSCTX_INPROC_SERVER,IID_IBaseFilter,(void**)&pNull);
    if (FAILED(hr))
        return hr;
    return hr;
}

檢測(cè)設(shè)備

//遍歷設(shè)備，找到指定vidpid設(shè)備后打開(kāi)設(shè)備
HRESULT InitMonikers()
{
    USES_CONVERSION;
    HRESULT hr;
    ULONG cFetched;

    //https://docs.microsoft.com/zh-cn/windows/desktop/DirectShow/selecting-a-capture-device
    //遍歷設(shè)備
    ICreateDevEnum *pCreateDevEnum;
    hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER, IID_ICreateDevEnum, (void**)&pCreateDevEnum);
    if (FAILED(hr))
    {
        printf("Failed to enumerate all video and audio capture devices!  hr=0x%x\n", hr);
        return hr;
    }

    IEnumMoniker *pEnumMoniker;
    hr = pCreateDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pEnumMoniker, 0);
    if (FAILED(hr) || !pEnumMoniker)
    {
        printf("Failed to create ClassEnumerator!  hr=0x%x\n", hr);
        return -1;
    }

    while (hr = pEnumMoniker->Next(1, &pMonikerVideo, &cFetched), hr == S_OK)
    {
        IPropertyBag *pPropBag;
        //BindToStorage之后就可以訪問(wèn)設(shè)備標(biāo)識(shí)的屬性集了。
        HRESULT hr = pMonikerVideo->BindToStorage(0, 0, IID_PPV_ARGS(&pPropBag));
        if (FAILED(hr))
        {
            pMonikerVideo->Release();
            continue;
        }

        VARIANT var;
        VariantInit(&var);
        //DevicePath中包含vidpid
        hr = pPropBag->Read(L"DevicePath", &var, 0);
        if (FAILED(hr))
        {
            VariantClear(&var);
            pMonikerVideo->Release();
            continue;
        }

        //比較是否是要使用的設(shè)備
        //TRACE("Device path: %S\n", var.bstrVal);
        std::string devpath = std::string(W2A(var.bstrVal));
        if (devpath.find("vid_06f8&pid_3015") == -1)
        {
            VariantClear(&var);
            pMonikerVideo->Release();
            continue;
        }
        VariantClear(&var);

        // BindToObject將某個(gè)設(shè)備標(biāo)識(shí)綁定到一個(gè)DirectShow Filter，
        //     然后調(diào)用IFilterGraph::AddFilter加入到Filter Graph中，這個(gè)設(shè)備就可以參與工作了
        // 調(diào)用IMoniker::BindToObject建立一個(gè)和選擇的device聯(lián)合的filter，
        //      并且裝載filter的屬性(CLSID,FriendlyName, and DevicePath)。
        hr = pMonikerVideo->BindToObject(0, 0, IID_IBaseFilter, (void**)&pVideoCaptureFilter);
        if (FAILED(hr))
        {
            printf("Couldn't bind moniker to filter object!  hr=0x%x\n", hr);
            return hr;
        }

        pPropBag->Release();
        pMonikerVideo->Release();
    }

    pEnumMoniker->Release();
    return hr;
}

構(gòu)建預(yù)覽Graph

//開(kāi)始構(gòu)建預(yù)覽graph
    //加入設(shè)備抓拍filter
    hr = pGraphBuilder->AddFilter(pVideoCaptureFilter, L"Video Capture");
    if (FAILED(hr))
    {
        printf("Couldn't add video capture filter to graph!  hr=0x%x\n", hr);
        pVideoCaptureFilter->Release();
        return hr;
    }

    //加入DirectShow中自帶的SampleGrabber Filter
    hr = pGraphBuilder->AddFilter(pGrabberF, L"Sample Grabber");
    if (FAILED(hr))
    {
        printf("Couldn't add sample grabber to graph!  hr=0x%x\n", hr);
        // Return an error.
    }

    //使用Capture Graph Builder構(gòu)建預(yù)覽 Graph
    hr = pCaptureGraphBuilder2->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, pVideoCaptureFilter, pGrabberF, 0 );
    if (FAILED(hr))
    {
        printf("Couldn't render video capture stream. The device may already be in use.  hr=0x%x\n", hr);
        pVideoCaptureFilter->Release();
        return hr;
    }

構(gòu)建抓拍Graph

    //加入DirectShow中自帶的SampleGrabber Filter
    hr = pGraphBuilder->AddFilter(pGrabberStill, L"Still Sample Grabber");
    if (FAILED(hr))
    {
        printf("Couldn't add sample grabber to graph!  hr=0x%x\n", hr);
        // Return an error.
    }

    //加入DirectShow中自帶的NullRender Filter
    hr = pGraphBuilder->AddFilter(pNull, L"NullRender");
    if (FAILED(hr))
    {
        printf("Couldn't add null to graph!  hr=0x%x\n", hr);
        return hr;
    }

    //使用Capture Graph Builder構(gòu)建抓拍 Graph
    hr = pCaptureGraphBuilder2->RenderStream(&PIN_CATEGORY_STILL, &MEDIATYPE_Video, pVideoCaptureFilter, pGrabberStill, pNull);
    if (FAILED(hr))
    {
        printf("Couldn't render video capture stream. The device may already be in use.  hr=0x%x\n", hr);
        pVideoCaptureFilter->Release();
        return hr;
    }

    //configure the Sample Grabber so that it buffers samples :
    hr = pSampleGrabberStill->SetOneShot(FALSE);
    hr = pSampleGrabberStill->SetBufferSamples(TRUE);

    //獲取設(shè)備輸出格式信息
    AM_MEDIA_TYPE mt;
    hr = pSampleGrabber->GetConnectedMediaType(&mt);
    if (FAILED(hr))
    {
        return -1;
    }
    VIDEOINFOHEADER * vih = (VIDEOINFOHEADER*)mt.pbFormat;
    CSampleGrabberCB *CB = new CSampleGrabberCB();
    if (!FAILED(hr))
    {
        CB->Width = vih->bmiHeader.biWidth;
        CB->Height = vih->bmiHeader.biHeight;
    }

    //設(shè)置觸發(fā)抓拍后，調(diào)用的回調(diào)函數(shù) 0-調(diào)用SampleCB 1-BufferCB
    hr = pSampleGrabberStill->SetCallback(CB, 1);
    if (FAILED(hr))
    {
        printf("set still trigger call back failed\n");
    }

啟動(dòng)Graph

    //設(shè)置預(yù)覽窗口大小位置
    SetupVideoWindow();

    //啟動(dòng)設(shè)備
    hr = pMediaControl->Run();
    if (FAILED(hr))
    {
        printf("Couldn't run the graph!  hr=0x%x\n", hr);
        return hr;
    }
    else 
        psCurrent = Running;

使用GraphEdt進(jìn)行調(diào)試

GraphEdt.exe是windows sdk中的graph調(diào)試工具，使用方法簡(jiǎn)介如下：

  1. 查看設(shè)備
    在Graph菜單中點(diǎn)擊Insert Filters，找到Video Capture Sources


    微信圖片_20181018093403.png

    可以看到設(shè)備信息，點(diǎn)擊Insert Filter可以將設(shè)備Filter加入到Graph中。

  2. 構(gòu)建Graph
    如果不清楚設(shè)備FIlter后邊應(yīng)該假如什么Filter，可以在Filter的Pin上右鍵，選擇Render Filter，會(huì)自動(dòng)連接一個(gè)Video Render。
    微信圖片_20181018093830.png

    此時(shí)點(diǎn)擊播放按鈕，可以看到視頻

源碼

github

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