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  1. #1
    Join Date
    Mar 2015
    Posts
    2

    New Process() freezes program until it finishes?

    Hello everyone, I am calling up FFMPEG and passing arguments to it to transcode video files. The program works great with my existing code, however when it is working on any larger files, I noticed that my program freezes while FFMPEG is running. As it runs, I read the standard error output, which give me status and progress updates about twice a second.

    I know the problem is in Synchronous vs Asynchronous processes, but the sample code I have seen for Async Processes only appears to check for the output once, whereas I need to read it continuously as it comes available. I have a "kill-switch" which I want to check periodically to be able to abort the process, but once I call FFMPEG, it doesn't get read until after it has finished... There has to be a way to run asynchronous and still continuously monitor the output, right?


    Code:
                            Process proc = new Process();
                            proc.StartInfo.FileName = "C:\\FFMPEG\\bin\\ffmpeg.exe";
                            proc.StartInfo.Arguments = "-i " + sourceFile + "-c:v dnxhd -b:v 185M -r 29.97 -s 1920x1080 -pix_fmt yuv422p10le -flags +ildct -c:a pcm_s24le -ar 48k dnxhdoutput.mov";
                            proc.StartInfo.RedirectStandardError = true;
                            proc.StartInfo.RedirectStandardOutput = true;
                            proc.StartInfo.CreateNoWindow = true;
                            proc.StartInfo.UseShellExecute = false;
                            proc.EnableRaisingEvents = true;
    
                            if (!proc.Start())
                            {
                                Console.WriteLine("Error starting");
                                return;
                            }
    
                            StreamReader reader = proc.StandardError;
                            string line;
                            string fileName = Path.GetFileName(Item.Text); //get the filename without path...
                            int fileNum = Item.Index + 1;
                            while ((line = reader.ReadLine()) != null)
                            {
                                Console.WriteLine(line);
                                labelStatus.Text = fileNum + " of " + fileList1.CheckedIndices.Count + ": " + fileName + " - " + line;
                                labelStatus.Update();
    
                                //Check for Kill Switch!
                                //if (checkKill.Checked == true)
                                //{
                                //    proc.Close();
                                //}
    
                            }
                            proc.Close();

  2. #2
    Join Date
    Mar 2002
    Location
    St. Petersburg, Florida, USA
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    12,117

    Re: New Process() freezes program until it finishes?

    One way (which I use a lot) is to wrap the synchronous code (that is working) into a clean class structure, and then invoke the method on that class asynchronously (e.g. so that it runs on a separate thread). Now the communication between the processes is synchronous, but the communication by the threads is async!
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  3. #3
    Join Date
    Mar 2015
    Posts
    2

    Re: New Process() freezes program until it finishes?

    I will have to try that. Sounds like something I would do

    Here is another approach I took, but still causing the freezing...

    Code:
    void StartProcess(string arguments)
            {
                var process = new Process
                {
                    StartInfo = new ProcessStartInfo
                    {
                        FileName = "C:\\FFMPEG\\bin\\ffmpeg.exe",
                        Arguments = arguments,
                        UseShellExecute = false,
                        RedirectStandardOutput = true,
                        RedirectStandardError = true,
                        CreateNoWindow = true,
                    }
                };
    
                process.OutputDataReceived += (sender, args) => Display(args.Data);
                process.ErrorDataReceived += (sender, args) => Display(args.Data);
    
                process.Start();
                process.BeginOutputReadLine();
                process.BeginErrorReadLine();
    
                process.WaitForExit(); //you need this in order to flush the output buffer
            }
    
            void Display(string output)
            {
                Console.WriteLine(output);
            }

  4. #4
    Arjay's Avatar
    Arjay is offline Moderator / EX MS MVP Power Poster
    Join Date
    Aug 2004
    Posts
    13,495

    Re: New Process() freezes program until it finishes?

    Quote Originally Posted by iBkickinit View Post
    I will have to try that. Sounds like something I would do

    Here is another approach I took, but still causing the freezing...

    Code:
    void StartProcess(string arguments)
            {
                var process = new Process
                {
                    StartInfo = new ProcessStartInfo
                    {
                        FileName = "C:\\FFMPEG\\bin\\ffmpeg.exe",
                        Arguments = arguments,
                        UseShellExecute = false,
                        RedirectStandardOutput = true,
                        RedirectStandardError = true,
                        CreateNoWindow = true,
                    }
                };
    
                process.OutputDataReceived += (sender, args) => Display(args.Data);
                process.ErrorDataReceived += (sender, args) => Display(args.Data);
    
                process.Start();
                process.BeginOutputReadLine();
                process.BeginErrorReadLine();
    
                process.WaitForExit(); //you need this in order to flush the output buffer
            }
    
            void Display(string output)
            {
                Console.WriteLine(output);
            }
    The following line causes the launched program to be synchronous (and freezes your UI).
    Code:
    process.WaitForExit(); //you need this in order to flush the output buffer
    As CPU mentioned, you need to start that process from another (non-UI) thread.

  5. #5
    Join Date
    Mar 2002
    Location
    St. Petersburg, Florida, USA
    Posts
    12,117

    Re: New Process() freezes program until it finishes?

    Quote Originally Posted by Arjay View Post
    As CPU mentioned, you need to start that process from another (non-UI) thread.
    I never said "need to"... The "WaitForExit" could be removed and logic written to use the "Exited" event [ https://msdn.microsoft.com/en-us/lib...v=vs.110).aspx ].

    However, I rarely use that approach as implementing proper cleanup of all of the associated async structures can be quite difficult (and therefore error prone).
    TheCPUWizard is a registered trademark, all rights reserved. (If this post was helpful, please RATE it!)
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