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();

---

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!

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);
        }

---

Quote:

---

Originally Posted by iBkickinit

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.

Quote:

---

Originally Posted by Arjay

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).