什么是UVC攝像頭颈嚼，UVC是什么意思笆载？
UVC是一種標準的USB視頻設(shè)備協(xié)議饲常，就是傳說中的免驅(qū)攝像頭。UVC是Usb Video Class的簡稱搁料。
Windows平臺上UVC驅(qū)動文檔
DirectShow簡介
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)的流媒體處理的開發(fā)包或详，與DirectX開發(fā)包一起發(fā)布系羞。DirectShow使用一種叫Filter Graph的模型來管理整個數(shù)據(jù)流的處理過程，運用DirectShow霸琴，我們可以很方便地從支持WDM驅(qū)動模型的采集卡上捕獲數(shù)據(jù)椒振，并且進行相應的后期處理乃至存儲到文件中。這樣使在多媒體數(shù)據(jù)庫管理系統(tǒng)（MDBMS）中多媒體數(shù)據(jù)的存取變得更加方便梧乘。它廣泛地支持各種媒體格式澎迎，包括Asf、Mpeg选调、Avi夹供、Dv、Mp3仁堪、Wave等哮洽，為多媒體流的捕捉和回放提供了強有力的支持。
調(diào)用DirectShow獲取攝像頭按鍵后的抓拍圖片
Filter
DirectShow使用模塊化體系結(jié)構(gòu)弦聂，其中每個處理階段都由稱為filter的COM對象完成鸟辅。 DirectShow為應用程序提供了一組標準filter，開發(fā)人員可以編寫自己的自定義過濾器來擴展DirectShow的功能莺葫。
Graph
有多個Filter連接匪凉，構(gòu)成Graph。Filter Graph Manager用來構(gòu)建和控制Graph中的Filter
代碼實戰(zhàn)
初始化各個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接口捺檬，用來控制流媒體在Filter Graph中的流動再层，例如流媒體的啟動和停止；
hr = pGraphBuilder->QueryInterface(IID_IMediaControl,(LPVOID *) &pMediaControl);
if (FAILED(hr))
return hr;
// IVideoWindow,用來顯示預覽視頻
hr = pGraphBuilder->QueryInterface(IID_IVideoWindow, (LPVOID *) &pVideoWindow);
if (FAILED(hr))
return hr;
// IMediaEvent接口堡纬，該接口在Filter Graph發(fā)生一些事件時用來創(chuàng)建事件的標志信息并傳送給應用程序
hr = pGraphBuilder->QueryInterface(IID_IMediaEvent,(LPVOID *) &pMediaEvent);
if (FAILED(hr))
return hr;
//創(chuàng)建用于預覽的Sample Grabber Filter.
hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER,
IID_IBaseFilter, (void**)&pGrabberF);
if (FAILED(hr))
return hr;
//獲取ISampleGrabber接口聂受，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;
}
檢測設(shè)備
//遍歷設(shè)備隐轩，找到指定vidpid設(shè)備后打開設(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之后就可以訪問設(shè)備標識的屬性集了。
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將某個設(shè)備標識綁定到一個DirectShow Filter渤早，
// 然后調(diào)用IFilterGraph::AddFilter加入到Filter Graph中职车，這個設(shè)備就可以參與工作了
// 調(diào)用IMoniker::BindToObject建立一個和選擇的device聯(lián)合的filter，
// 并且裝載filter的屬性(CLSID,FriendlyName, and DevicePath)鹊杖。
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)建預覽Graph
//開始構(gòu)建預覽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)抓拍后悴灵，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Graph
//設(shè)置預覽窗口大小位置
SetupVideoWindow();
//啟動設(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進行調(diào)試
GraphEdt.exe是windows sdk中的graph調(diào)試工具，使用方法簡介如下：
-
查看設(shè)備
在Graph菜單中點擊Insert Filters骂蓖，找到Video Capture Sources
微信圖片_20181018093403.png
可以看到設(shè)備信息积瞒，點擊Insert Filter可以將設(shè)備Filter加入到Graph中。
- 構(gòu)建Graph
如果不清楚設(shè)備FIlter后邊應該假如什么Filter茫孔，可以在Filter的Pin上右鍵叮喳，選擇Render Filter，會自動連接一個Video Render缰贝。
微信圖片_20181018093830.png
此時點擊播放按鈕剩晴，可以看到視頻
