private string RevertToTime(int l)//转换为时分秒格式
    {
        string str = "";
        int hour = 0;
        int minute = 0;
        int second = 0;

        second = l / 1000;

        if (second > 60)
        {
            minute = second / 60;
            second = second % 60;
        }
        if (minute > 60)
        {
            hour = minute / 60;
            minute = minute % 60;
        }
        return (hour.ToString() + ":" + minute.ToString() + ":"
                + second.ToString());
    }