#region 截图
        //fileName flv文件地址
        //imgFile 输出的图片地址
        public string CatchImg(string fileName,string imgFile)
        {
            //
            string ffmpeg = VideoDecoder.ffMpeg; //ffmpeg执行文件的路径
            //
            string flv_img =imgFile+".jpg";
            //
            string FlvImgSize = VideoDecoder.sizeOfImg;//生成的图片分辨率 240x180
            //
            System.Diagnostics.ProcessStartInfo ImgstartInfo = new System.Diagnostics.ProcessStartInfo(ffmpeg);
            ImgstartInfo.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
            //
            ImgstartInfo.Arguments = "   -i   " + fileName + "  -y  -f  image2   -ss 2 -vframes 1  -s   " + FlvImgSize + "   " + flv_img;
            try
            {
                System.Diagnostics.Process.Start(ImgstartInfo);
            }
            catch
            {
                return "";
            }
            //
            if (System.IO.File.Exists(flv_img))
            {
                return flv_img;
            }

            return "";
        }
        #endregion

------解决方案--------------------

http://topic.csdn.net/u/20070212/11/16EE743D-32D8-4252-B5D6-26DAA1082FBE.html
http://topic.csdn.net/u/20070620/13/4BE90E90-95FA-464D-A4F3-85CC694D5655.html