c#将控制台输出读取为字符串的问题

Question

我想从我的应用程序启动ffmpeg并检索ffmpeg产生的所有控制台输出。事情似乎很明显，我跟随了许多论坛的帖子/文章，但我有问题，尽管我遵循了所有的信息，但我似乎最终陷入了死胡同。

应该包含ffmpeg输出的字符串总是空的。我试着看看问题出在哪里，所以我做了一个简单的c#控制台应用程序，只列出所有传递给ffmpeg的执行参数，只是为了检查问题是否由ffmpeg本身引起。在这种情况下，一切都按预期进行。

我也预览了我的应用程序的控制台窗口。当我启动ffmpeg时，我看到控制台中的所有输出，但是应该接收输出以进一步处理报告的函数该字符串为空。当我的参数列表应用程序启动时，我看到的唯一一件事就是得到输出的函数的预期报告。

所以我的问题是怎么做才能得到ffmpeg输出，因为我打算在第一。

提前感谢m

Answer 1

这是一个很长的镜头，但是你试过重定向标准错误吗?

Answer 2

这是我的ffmpeg包装器类的一部分，特别展示了如何从ffmpeg收集输出和错误。

我把进程放在GetVideoDuration()函数中，这样你就可以在一个地方看到所有的东西。

设置:

我的ffmpeg在桌面上，ffPath是用来指向它的

namespace ChildTools.Tools
{
    public class FFMpegWrapper
    {
        //path to ffmpeg (I HATE!!! MS special folders)
        string ffPath = System.Environment.GetFolderPath(Environment.SpecialFolder.Desktop) + "\ffmpeg.exe";
    //outputLines receives each line of output, only if they are not zero length
        List<string> outputLines = new List<string>();

    //In GetVideoDuration I only want the one line of output and in text form.
    //To get the whole output just remove the filter I use (my search for 'Duration') and either return the List<>
    //Or joint the strings from List<> (you could have used StringBuilder, but I find a List<> handier.
        public string GetVideoDuration(FileInfo fi)
        {
            outputLines.Clear();
    //I only use the information flag in this function
            string strCommand = string.Concat(" -i "", fi.FullName, """);
    //Point ffPath to my ffmpeg
            string ffPath = System.Environment.GetFolderPath(Environment.SpecialFolder.Desktop) + "\ffmpeg.exe";
            Process processFfmpeg = new Process();
            processFfmpeg.StartInfo.Arguments = strCommand;
            processFfmpeg.StartInfo.FileName = ffPath;
    //I have to say that I struggled for a while with the order that I setup the process.
    //But this order below I know to work

            processFfmpeg.StartInfo.UseShellExecute = false;
            processFfmpeg.StartInfo.RedirectStandardOutput = true;
            processFfmpeg.StartInfo.RedirectStandardError = true;
            processFfmpeg.StartInfo.CreateNoWindow = true;
            processFfmpeg.ErrorDataReceived += processFfmpeg_OutData;
            processFfmpeg.OutputDataReceived += processFfmpeg_OutData;
            processFfmpeg.EnableRaisingEvents = true;
            processFfmpeg.Start();
            processFfmpeg.BeginOutputReadLine();
            processFfmpeg.BeginErrorReadLine();
            processFfmpeg.WaitForExit();
    //I filter the lines because I only want 'Duration' this time
            string oStr = "";
            foreach (string str in outputLines)
            {
                if (str.Contains("Duration"))
                {
                    oStr = str;
                }
            }
    //return a single string with the duration line
            return oStr;
        }
        private void processFfmpeg_OutData(object sender, DataReceivedEventArgs e)
        {
    //The data we want is in e.Data, you must be careful of null strings
            string strMessage = e.Data;
            if outputLines != null && strMessage != null && strMessage.Length > 0)
            {
                outputLines.Add(string.Concat( strMessage,"n"));
        //Try a Console output here to see all of the output. Particularly
        //useful when you are examining the packets and working out timeframes
        //Console.WriteLine(strMessage);
            }
        } 
    }
}