此操作需要借助于 ffmpeg.exe 文件，使用时要注意，文件需要有读写权限和 .net 调用 ffmpeg 的权限。

以下是代码片段：

            if (MoveFileName.Substring(MoveFileName.LastIndexOf(".")) == ".wmv" || MoveFileName.Substring(MoveFileName.LastIndexOf(".")) == ".3gp")
            {
                //程序截图
                string ffmpeg = Server.MapPath("ffmpeg/ffmpeg.exe");
                string move = Server.MapPath("upfile/" + RMoveFileName);
                pic = Myfunction.MakeNum(5) + Myfunction.MakeFileName() + ".jpg";
                Process p = new Process();
                p.StartInfo.FileName = ffmpeg;
                p.StartInfo.Arguments = "-i " + move + " -y -f image2 -t 0.001 -s 120*120 " + Server.MapPath("upfile/img/" + pic);
                p.StartInfo.UseShellExecute = false;
                p.StartInfo.CreateNoWindow = true;
                p.StartInfo.RedirectStandardOutput = true;
                try
                {
                    p.Start();
                    p.Dispose();
                    p.Close();
                }
                catch (Exception ee)
                {
                    Response.Write(ee.ToString());
                }
            }