编程获取视频缩略图

如何截取视频图片示例
//自定义类实现截取视频路径和保存路径
  //获取转换工具路径
    public static string ffmpegtool = ConfigurationManager.AppSettings["ffmpeg"];
    //获取视频的文件夹名
    public static string upFile = "upfile/";
    //获取图片文件的文件夹名
    public static string imgFile = "imgFile/";
    //获取转换后文件的文件夹名
    public static string playFile = "playFile/";
    //文件图片大小
    public static string sizeOfImg = ConfigurationManager.AppSettings["imgSize"];
    //文件大小
    public static string widthOfFile = ConfigurationManager.AppSettings["widthSize"];
    public static string heightOfFile = ConfigurationManager.AppSettings["heightSize"];
//截取视频图片
  public static void catchImg(string fileName,string imgFile)
    {
        //获取截图工具路径
        string ffmpeg = System.Web.HttpContext.Current.Server.MapPath("../") + ffmpegtool;
        //获取截图后保存的路径
        string flv_img = imgFile;
        //获取截取图片的大小
        string FlvImgSize = sizeOfImg;
        Process pss = new Process();
        //设置启动程序的路径
        pss.StartInfo.FileName = ffmpeg;
        pss.StartInfo.Arguments = "   -i   " + fileName + "  -y  -f  image2   -ss 2 -vframes 1  -s   " + FlvImgSize + "   " + flv_img;
        //启动进程
        pss.Start();
    }//codego.net/tags/11/1/
    // 过滤HTML字符
    // <param name="str">传入需要过滤的字符串</param>
    // <returns>返回过滤后的字符串</returns>
    public static string filtrateHtml(string str)
    {
        str = str.Trim();
        str = str.Replace("'", """);
        str = str.Replace("<", "<");
        str = str.Replace(">", ">");
        str = str.Replace(" ", " ");
        str = str.Replace("\n", "<br>");
        return str;
    }
    // 恢复HTML字符
    // <param name="str">传入需要回复的字符串</param>
    // <returns>返回回复后的字符串</returns>
    public static string resumeHtml(string str)
    {
        str = str.Trim();
        str = str.Replace(""", "'");
        str = str.Replace("<", "<");
        str = str.Replace(">", ">");
        str = str.Replace(" ", " ");
        str = str.Replace("<br>", "\n");
        return str;
    }

http://blog.csdn.net/yyz_2637/article/details/6313586
http://bbs.csdn.net/topics/380172482

使用了以下命令：
ffmpeg.exe -i aaa.mp4 -y -f image2 -ss 2 -vframes 1 -s 240x320 1.jpg结果得到一个一片黑的图片啊

用ffmpeg获取的是全黑图片啊

if (hwnd == IntPtr.Zero)
                {
                    return null;
                }
                SystemApi.RECT rc = new SystemApi.RECT();
                SystemApi.GetWindowRect(hwnd, out rc);
                SystemApi.PointApi p = new SystemApi.PointApi();
                SystemApi.ScreenToClient(hwnd, out p);
                //设置客户区的坐标
                SimulatorInfo.MainClientLack = new Point(Math.Abs(p.x) - rc.left, Math.Abs(p.y) - rc.top);                SystemApi.RECT rcc = new SystemApi.RECT();
                SystemApi.GetClientRect(hwnd, out rcc);
                dc1 = SystemApi.CreateDC("DISPLAY", null,
                    null, (IntPtr)null);
                //创建显示器的DC
                Graphics g1 = Graphics.FromHdc(dc1);
                //由一个指定设备的句柄创建一个新的Graphics对象
                MyImage = new Bitmap(rcc.right, rcc.bottom, g1);
                //根据屏幕大小创建一个与之相同大小的Bitmap对象
                Graphics g2 = Graphics.FromImage(MyImage);
                //获得屏幕的句柄
                dc3 = g1.GetHdc();
                //获得位图的句柄
                dc2 = g2.GetHdc();
                //把当前屏幕捕获到位图对象中
                SystemApi.BitBlt(dc2, 0, 0, rcc.right,
                    rcc.bottom,
                    dc3, Math.Abs(p.x), Math.Abs(p.y), 13369376);
                //把当前屏幕拷贝到位图中
                g1.ReleaseHdc(dc3);
                //释放屏幕句柄
                g2.ReleaseHdc(dc2);
                //释放位图句柄
                g1.Dispose();
                g2.Dispose();
                return MyImage;
[DllImport("user32.dll")]
        public static extern int ScreenToClient(IntPtr hWnd, out PointApi lpRect);
        public struct PointApi
        {
            public int x;
            public int y;
        }
        [DllImport("user32.dll")]
        public static extern int GetClientRect(IntPtr hWnd, out RECT lpRect);
        [DllImport("user32.dll")]
        public static extern int GetWindowRect(IntPtr hWnd, out RECT lpRect);
        [StructLayout(LayoutKind.Sequential)]
        public struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }
        [DllImport("gdi32.dll")]
        public static extern IntPtr CreateDC(
         string lpszDriver,        // driver name驱动名
         string lpszDevice,        // device name设备名
         string lpszOutput,        // not used; should be NULL
         IntPtr lpInitData  // optional printer data
         );
        [DllImport("gdi32.dll")]
        public static extern bool BitBlt(
            IntPtr hdcDest, // 目标 DC的句柄
            int nXDest,
            int nYDest,
            int nWidth,
            int nHeight,
            IntPtr hdcSrc, // 源DC的句柄
            int nXSrc,
            int nYSrc,
            int dwRop // 光栅的处理数值
            );
        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr FindWindow(string className, string windowTitle);
        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr FindWindowEx(IntPtr parentHandle, IntPtr childAfter, string className, string windowTitle);

        [DllImport("user32.dll", EntryPoint = "SendMessage")]
        public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);        public static void Click(IntPtr mnqhwnd, Point P)
        {
            SendMessage(mnqhwnd, 0x201, 0, MakeLParam(P.X, P.Y));
            SendMessage(mnqhwnd, 0x202, 0, MakeLParam(P.X, P.Y));
        }
        public static int MakeLParam(int LoWord, int HiWord)
        {
            return ((HiWord << 16) | (LoWord & 0xffff));
        }

不希望使用第三方工具，如ffmpeg.
也不是播放视频时截图。要实现像Windows资源管理器里面显示视频文件的缩略图那样。
想知道Windows自己是怎么做到的。应该是通过Shell API吧。
查到了Windows有个API：IThumbnailCache，但实在不知道怎么用，尤其在C#下面。

调试易

编程获取视频缩略图

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