ffmpeg获取文件的总时长（mp3/mp4/flv等）

使用ffmpeg.exe获取文件属性信息，C#中可以在进程外异步调用这个工具，如下：

using (System.Diagnostics.Process pro = new System.Diagnostics.Process())
{
    pro.StartInfo.UseShellExecute = false;
    pro.StartInfo.ErrorDialog = false;
    pro.StartInfo.RedirectStandardError = true;
    pro.StartInfo.FileName = AppDomain.CurrentDomain.BaseDirectory + "ffmpeg.exe";
    pro.StartInfo.Arguments = " -i " + fileName;
    pro.Start();
    System.IO.StreamReader errorreader = pro.StandardError;
    pro.WaitForExit(1000);
    string result = errorreader.ReadToEnd();
    if (!string.IsNullOrEmpty(result))
    {
        result = result.Substring(result.IndexOf("Duration: ") + ("Duration: ").Length, ("00:00:00").Length);
        duration = result;
    }
}