c#获取Amr文件的时长（毫秒）亲测有效

/// <summary>
        /// c#获取Amr文件的时长（毫秒）
        /// </summary>
        /// <param name="fileName">文件路径</param>
        /// <returns></returns>
        private long GetAMRFileDuration(string fileName)
        {
            long duration = ;
            FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
            {
                byte[] packed_size = { , , , , , , , , , , , , , , ,  };
                int pos = ;
                pos += ;
                long lenth = fs.Length;
                byte[] toc = new byte[];
                int framecount = ;
                byte ft;
                while (pos < lenth)
                {
                    fs.Seek(pos, SeekOrigin.Begin);
                    if ( != fs.Read(toc, , ))
                    {
                        fs.Close();
                        break;
                    }
                    ft = (byte)((toc[] / ) & 0x0F);
                    pos += packed_size[ft] + ;
                    framecount++;
                }
                duration = framecount * ;
            }
            fs.Close();
            return duration;
        }