Directshow_驱动摄像头预览视频

超、凢脫俗 2022-12-15 12:46 11阅读 0赞

[https://blog.csdn.net/li\_chihang/article/details/43378429?utm\_medium=distribute.pc\_relevant\_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel\_param&depth\_1-utm\_source=distribute.pc\_relevant\_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel\_param][https_blog.csdn.net_li_chihang_article_details_43378429_utm_medium_distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param_depth_1-utm_source_distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param]

出于兴趣一直以来都断断续续看过dshow的东西，可没怎么系统地总结过(学习还是要多实践，多总结啊).

dshow预览摄像头捕捉的视频比较简单基础，网上相关的资料很多，简单的思路由下面代码所示:

1.  `ICaptureGraphBuilder2 *pBuild; // Capture Graph Builder`
2.  `// Initialize pBuild (not shown).`
3.  `IBaseFilter *pCap; // Video capture filter.`
4.  `/* Initialize pCap and add it to the filter graph (not shown). */`
5.  `hr = pBuild->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video,`
6.  `pCap, NULL, NULL);`

dshow 提供了一个 Capture Graph Builder COM 组件使得捕捉graph 图的生成更加简单。 Capture Graph Builder 提供了一 ICaptureGraphBuilder2接口 ，这个接口提供了一些方法用来构建和控制捕捉 graph。video capture filter则由系统设备枚举得到可用视频设备，并生成filter；最后智能连接graph即可.具体见代码和注释:

1.  `#include <dshow.h>`
2.  `#include <stdio.h>`
3.  `#include <atlconv.h>`
4.  `#pragma comment(lib,"quartz.lib")`
5.  `#pragma comment(lib, "strmiids.lib")`
6.  `void main()`
7.  `{`
8.  `IGraphBuilder *pGraph = NULL;`
9.  `IMediaControl *pControl = NULL;`
10. `IMediaEvent *pEvent = NULL;`
11. `IVideoWindow *pVideoWindow = NULL;`
12. `ICaptureGraphBuilder2 *pBuild = NULL;`
13. `// Initialize the COM library.`
14. `HRESULT hr = CoInitialize(NULL);`
15. `if (FAILED(hr)){`
16. `printf("ERROR - Could not initialize COM library");`
17. `return;`
18. `}`
19. `//创建Capture Graph Builder 对象`
20. `hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL,`
21. `CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2, (void**)&pBuild);`
22. `if (SUCCEEDED(hr)){`
23. `// 创建 graph manger 对象.`
24. `hr = CoCreateInstance(CLSID_FilterGraph, 0, CLSCTX_INPROC_SERVER,`
25. `IID_IGraphBuilder, (void**)&pGraph);`
26. `if (SUCCEEDED(hr))`
27. `// 初始化 Capture Graph Builder.`
28. `pBuild->SetFiltergraph(pGraph);`
29. `}`
30. `//各个查询接口.`
31. `hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);`
32. `hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);`
33. `hr = pGraph->QueryInterface(IID_IVideoWindow, (void**)&pVideoWindow);`
34. 
35. `ICreateDevEnum *pDevEnum = NULL;`
36. `IEnumMoniker *pEnum = NULL;`
37. `//创建一个系统设备枚举对象`
38. `hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL,`
39. `CLSCTX_INPROC_SERVER, IID_ICreateDevEnum,reinterpret_cast<void**>(&pDevEnum));`
40. `if (SUCCEEDED(hr))`
41. `//创建一个枚举器，用来枚举视频设备`
42. `hr = pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory,&pEnum, 0);`
43. 
44. `IMoniker *pMoniker = NULL;`
45. `//开始枚举设备`
46. `while (pEnum->Next(1, &pMoniker, NULL) == S_OK)`
47. `{`
48. `IBaseFilter *pCap = NULL;`
49. `hr = pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pCap);//为设备生成 filter`
50. `if (SUCCEEDED(hr))`
51. `{`
52. `hr = pGraph->AddFilter(pCap, L"Capture Filter");//将filter加入到graph`
53. `}`
54. `if (SUCCEEDED(hr))`
55. `{`
56. `//PIN_CATEGORY_PREVIEW: specifying a pin category;`
57. `//MEDIATYPE_Video: the major media types.`
58. `//pCap: pointer to the starting filter for the connection`
59. `hr = pBuild->RenderStream(&PIN_CATEGORY_PREVIEW,&MEDIATYPE_Video, pCap, NULL, NULL);//连接graph`
60. `break;`
61. `}`
62. `else{`
63. `pMoniker->Release();`
64. `continue; //尝试下一个`
65. `}`
66. `}`
67. `pVideoWindow->put_AutoShow(OATRUE);//graph自动显示视频窗口`
68. `//pVideoWindow->put_Visible(OATRUE/*OAFALSE*/);`
69. `if (SUCCEEDED(hr))`
70. `{`
71. `// Run the graph.`
72. `hr = pControl->Run();`
73. `if (SUCCEEDED(hr)){`
74. `long evCode;`
75. `pEvent->WaitForCompletion(INFINITE, &evCode);//一直阻塞在这边;`
76. `}`
77. `}`
78. `pBuild->Release();`
79. `pMoniker->Release();`
80. `pControl->Release();`
81. `pEvent->Release();`
82. `pGraph->Release();`
83. `CoUninitialize();`
84. `}`

参考资料:

1.  《Directshow开发指南》
2.  《directshow SDK 学习笔记》

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