c++ - DirectShow 和 openCV。读取视频文件并处理

Question

我在 StackOverflow 上使用了搜索，但没有找到答案。我正在开发一个应用程序并使用 OpenCV，但我需要处理不同的视频（主要是 *.avi），所以我决定使用 DirectShow。我能够创建简单的应用程序，但我找不到任何解释如何从 *.avi 获取帧，而无需创建 ActiveWindow。事实上，我只需要使用 DirectShow 读取视频，然后我将使用 OpenCV 处理和显示视频。任何帮助表示赞赏。提前致谢！

请原谅我糟糕的英语。

Answer 1

创建一个带有 NULL 渲染的图形。另请查看 directshow SDK 中的示例抓取器示例。它显示了如何为图形抓取框架。然后，您可以将帧传递给 openCV 进行处理。

Answer 2

基本上你想连接这样的东西：

Source -> Sample Grabber -> Null renderer

下载 graphEdit 或 GraphEdit+，您可以直观地表示这些过滤器。作为示例，我继续构建了一个从本地网络摄像头到连接到空渲染器的示例抓取器的图表。GraphEdit+ 生成的 C# 代码是这样的：

//Don't forget to add reference to DirectShowLib in your project.
using System;
using System.Collections.Generic;
using System.Runtime.InteropServices.ComTypes;
using System.Runtime.InteropServices;
using DirectShowLib;

namespace graphcode
{
class Program
{
    static void checkHR(int hr, string msg)
    {
        if (hr < 0)
        {
            Console.WriteLine(msg);
            DsError.ThrowExceptionForHR(hr);
        }
    }

    static void BuildGraph(IGraphBuilder pGraph)
    {
        int hr = 0;

        //graph builder
        ICaptureGraphBuilder2 pBuilder = (ICaptureGraphBuilder2)new CaptureGraphBuilder2();
        hr = pBuilder.SetFiltergraph(pGraph);
        checkHR(hr, "Can't SetFiltergraph");

        Guid CLSID_SampleGrabber = new Guid("{C1F400A0-3F08-11D3-9F0B-006008039E37}"); //qedit.dll
        Guid CLSID_NullRenderer = new Guid("{C1F400A4-3F08-11D3-9F0B-006008039E37}"); //qedit.dll

        //add Integrated Camera
        IBaseFilter pIntegratedCamera = CreateFilter(@"@device:pnp:\\?\usb#vid_04f2&pid_b221&mi_00#7&34997cec&0&0000#{65e8773d-8f56-11d0-a3b9-00a0c9223196}\global");
        hr = pGraph.AddFilter(pIntegratedCamera, "Integrated Camera");
        checkHR(hr, "Can't add Integrated Camera to graph");

        //add SampleGrabber
        IBaseFilter pSampleGrabber = (IBaseFilter)Activator.CreateInstance(Type.GetTypeFromCLSID(CLSID_SampleGrabber));
        hr = pGraph.AddFilter(pSampleGrabber, "SampleGrabber");
        checkHR(hr, "Can't add SampleGrabber to graph");

        //add Null Renderer
        IBaseFilter pNullRenderer = (IBaseFilter)Activator.CreateInstance(Type.GetTypeFromCLSID(CLSID_NullRenderer));
        hr = pGraph.AddFilter(pNullRenderer, "Null Renderer");
        checkHR(hr, "Can't add Null Renderer to graph");

        //connect Integrated Camera and SampleGrabber
        hr = pGraph.ConnectDirect(GetPin(pIntegratedCamera, "Capture"), GetPin(pSampleGrabber, "Input"), null);
        checkHR(hr, "Can't connect Integrated Camera and SampleGrabber");

        //connect SampleGrabber and Null Renderer
        hr = pGraph.ConnectDirect(GetPin(pSampleGrabber, "Output"), GetPin(pNullRenderer, "In"), null);
        checkHR(hr, "Can't connect SampleGrabber and Null Renderer");

    }

    static void Main(string[] args)
    {
        try
        {
            IGraphBuilder graph = (IGraphBuilder)new FilterGraph();
            Console.WriteLine("Building graph...");
            BuildGraph(graph);
            Console.WriteLine("Running...");
            IMediaControl mediaControl = (IMediaControl)graph;
            IMediaEvent mediaEvent = (IMediaEvent)graph;
            int hr = mediaControl.Run();
            checkHR(hr, "Can't run the graph");
            bool stop = false;
            int n = 0;
            while (!stop)
            {
                System.Threading.Thread.Sleep(500);
                Console.Write(".");
                EventCode ev;
                IntPtr p1, p2;
                if (mediaEvent.GetEvent(out ev, out p1, out p2, 0) == 0)
                {
                    if (ev == EventCode.Complete || ev == EventCode.UserAbort)
                    {
                        Console.WriteLine("Done!");
                        stop = true;
                    }
                    else
                    if (ev == EventCode.ErrorAbort)
                    {
                        Console.WriteLine("An error occured: HRESULT={0:X}", p1);
                        mediaControl.Stop();
                        stop = true;
                    }
                    mediaEvent.FreeEventParams(ev, p1, p2);
                }
                // stop after 10 seconds
                n++;
                if (n > 20)
                {
                    Console.WriteLine("stopping..");
                    mediaControl.Stop();
                    stop = true;
                }
            }
        }
        catch (COMException ex)
        {
            Console.WriteLine("COM error: " + ex.ToString());
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error: " + ex.ToString());
        }
    }

    public static IBaseFilter CreateFilter(string displayName)
    {
        int hr = 0;
        IBaseFilter filter = null;
        IBindCtx bindCtx = null;
        IMoniker moniker = null;

        try
        {
            hr = CreateBindCtx(0, out bindCtx);
            Marshal.ThrowExceptionForHR(hr);

            int eaten;
            hr = MkParseDisplayName(bindCtx, displayName, out eaten, out moniker);
            Marshal.ThrowExceptionForHR(hr);

            Guid guid = typeof(IBaseFilter).GUID;
            object obj;
            moniker.BindToObject(bindCtx, null, ref guid, out obj);
            filter = (IBaseFilter)obj;
        }
        finally
        {
            if (bindCtx != null) Marshal.ReleaseComObject(bindCtx);
            if (moniker != null) Marshal.ReleaseComObject(moniker);
        }

        return filter;
    }

    [DllImport("ole32.dll")]
    public static extern int CreateBindCtx(int reserved, out IBindCtx ppbc);

    [DllImport("ole32.dll")]
    public static extern int MkParseDisplayName(IBindCtx pcb, [MarshalAs(UnmanagedType.LPWStr)] string szUserName, out int pchEaten, out IMoniker ppmk);

    static IPin GetPin(IBaseFilter filter, string pinname)
    {
        IEnumPins epins;
        int hr = filter.EnumPins(out epins);
        checkHR(hr, "Can't enumerate pins");
        IntPtr fetched = Marshal.AllocCoTaskMem(4);
        IPin[] pins = new IPin[1];
        while (epins.Next(1, pins, fetched) == 0)
        {
            PinInfo pinfo;
            pins[0].QueryPinInfo(out pinfo);
            bool found = (pinfo.name == pinname);
            DsUtils.FreePinInfo(pinfo);
            if (found)
                return pins[0];
        }
        checkHR(-1, "Pin not found");
        return null;
    }

}

}

您仍然需要实际捕获示例帧，但正如上面帖子中提到的，您可以查看 MSDN 上的 sampleGrabber SDK 以了解如何执行此操作。