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• C# execute external program and capture (stream) the output

  15 août 2018, par Roberto Correia

  I’m making a program to work with some video files.

  I’m using the ffmpeg executable to merge several files in a single file.
  This command takes several minutes to finish, so, I need a way to "monitor" the output, and show a progress bar on GUI.

  Looking at the following stackoverflow topics :

  • How to parse command line output from c# ?
  • Process.start : how to get the output ?
  • How To : Execute command line in C#, get STD OUT results

  I made this code :

  Process ffmpeg = new Process
  
  {
  
    StartInfo = 
  
    {
  
      FileName = @"d:\tmp\ffmpeg.exe",
  
      Arguments = "-f concat -safe 0 -i __sync.txt -c copy output.mp4",
  
      UseShellExecute = false,
  
      RedirectStandardOutput = true,
  
      CreateNoWindow = true,
  
      WorkingDirectory = @"d:\tmp"
  
    }
  
  }
  
  
  
  ffmpeg.EnableRaisingEvents = true;
  
  ffmpeg.OutputDataReceived += (s, e) => Debug.WriteLine(e.Data);
  
  ffmpeg.ErrorDataReceived += (s, e) => Debug.WriteLine($@"Error: {e.Data}");
  
  ffmpeg.Start();
  
  ffmpeg.BeginOutputReadLine();
  
  ffmpeg.WaitForExit();

  When I run this code, the ffmpeg start to merge files, I can see the ffmpeg process on Windows Task Manager, and if I wait long enough, the ffmpeg finish the job without any error. But, the Debug.WriteLine(e.Data) is never called (no output on Debug window). Tried to change to Console.WriteLine too (again, no output).

  So, after this, I tried this another version :

  Process ffmpeg = new Process
  
  {
  
    StartInfo = 
  
    {
  
      FileName = @"d:\tmp\ffmpeg.exe",
  
      Arguments = "-f concat -safe 0 -i __sync.txt -c copy output.mp4",
  
      UseShellExecute = false,
  
      RedirectStandardOutput = true,
  
      CreateNoWindow = true,
  
      WorkingDirectory = @"d:\tmp"
  
    }
  
  }
  
  
  
  ffmpeg.Start();
  
  while (!ffmpeg.StandardOutput.EndOfStream)
  
  {
  
    var line = ffmpeg.StandardOutput.ReadLine();
  
    System.Diagnostics.Debug.WriteLine(line);
  
    Console.WriteLine(line);
  
  }
  
  ffmpeg.WaitForExit();

  Again, the ffmpeg is started without any error, but the C# "hangs" on While (!ffmpeg.StandardOutput.EndOfStream) until ffmpeg is finished.

  If I execute the exact command on Windows prompt, a lot of output text is showed with progress of ffmpeg.

• C# execute external program and capture (stream) the output

  22 mars 2017, par Roberto Correia

  I’m making a program to work with some video files.

  I’m using the ffmpeg executable to merge several files in a single file.
  This command takes several minutes to finish, so, I need a way to "monitor" the output, and show a progress bar on GUI.

  Looking at the following stackoverflow topics :

  • How to parse command line output from c# ?
  • Process.start : how to get the output ?
  • How To : Execute command line in C#, get STD OUT results

  I made this code :

  Process ffmpeg = new Process
  
  {
  
    StartInfo = 
  
    {
  
      FileName = @"d:\tmp\ffmpeg.exe",
  
      Arguments = "-f concat -safe 0 -i __sync.txt -c copy output.mp4",
  
      UseShellExecute = false,
  
      RedirectStandardOutput = true,
  
      CreateNoWindow = true,
  
      WorkingDirectory = @"d:\tmp"
  
    }
  
  }
  
  
  
  ffmpeg.EnableRaisingEvents = true;
  
  ffmpeg.OutputDataReceived += (s, e) => Debug.WriteLine(e.Data);
  
  ffmpeg.ErrorDataReceived += (s, e) => Debug.WriteLine($@"Error: {e.Data}");
  
  ffmpeg.Start();
  
  ffmpeg.BeginOutputReadLine();
  
  ffmpeg.WaitForExit();

  When I run this code, the ffmpeg start to merge files, I can see the ffmpeg process on Windows Task Manager, and if I wait long enough, the ffmpeg finish the job without any error. But, the Debug.WriteLine(e.Data) is never called (no output on Debug window). Tried to change to Console.WriteLine too (again, no output).

  So, after this, I tried this another version :

  Process ffmpeg = new Process
  
  {
  
    StartInfo = 
  
    {
  
      FileName = @"d:\tmp\ffmpeg.exe",
  
      Arguments = "-f concat -safe 0 -i __sync.txt -c copy output.mp4",
  
      UseShellExecute = false,
  
      RedirectStandardOutput = true,
  
      CreateNoWindow = true,
  
      WorkingDirectory = @"d:\tmp"
  
    }
  
  }
  
  
  
  ffmpeg.Start();
  
  while (!ffmpeg.StandardOutput.EndOfStream)
  
  {
  
    var line = ffmpeg.StandardOutput.ReadLine();
  
    System.Diagnostics.Debug.WriteLine(line);
  
    Console.WriteLine(line);
  
  }
  
  ffmpeg.WaitForExit();

  Again, the ffmpeg is started without any error, but the C# "hangs" on While (!ffmpeg.StandardOutput.EndOfStream) until ffmpeg is finished.

  If I execute the exact command on Windows prompt, a lot of output text is showed with progress of ffmpeg.

• Extract individual frames from video and pipe them to StandardOutput in FFmpeg

  13 novembre 2019, par Nicke Manarin

  I’m trying to extract frames from a video using FFmpeg. But instead of letting FFmpeg write the files to disk, I’m trying to get the frames directly from StandardOutput.

  I’m not sure if it’s feasible. I’m expecting to get each frame individually as they get decoded by reading and waiting until all frames are extracted.

  With the current code, I think that I’m getting all frames at once.

  ---

  Command

  ffmpeg -i "C:\video.mp4" -r 30 -ss 00:00:10.000 -to 00:01:20.000 -hide_banner -c:v png -f image2pipe -

  Code

  var start = TimeSpan.FromMilliseconds(SelectionSlider.LowerValue);
  
  var end = TimeSpan.FromMilliseconds(SelectionSlider.UpperValue);
  
  
  
  var info = new ProcessStartInfo(UserSettings.All.FfmpegLocation)
  
  {
  
      Arguments = $" -i \"{VideoPath}\" -r {fps} -ss {start:hh\\:mm\\:ss\\.fff} " +
  
          "-to {end:hh\\:mm\\:ss\\.fff} -hide_banner -c:v png -f image2pipe -",
  
      CreateNoWindow = true,
  
      ErrorDialog = false,
  
      UseShellExecute = false,
  
      RedirectStandardError = true,
  
      RedirectStandardOutput = true
  
  };
  
  
  
  var process = new Process();
  
  process.StartInfo = info;
  
  process.Start();
  
  
  
  while (!process.StandardOutput.EndOfStream)
  
  {
  
      if (_cancelled)
  
      {
  
          process.Kill();
  
          return;
  
      }
  
  
  
      //This returns me the entire byte array, of all frames.
  
      var bytes = default(byte[]);
  
      using (var memstream = new MemoryStream())
  
      {
  
          process.StandardOutput.BaseStream.CopyTo(memstream);
  
          bytes = memstream.ToArray();
  
      }
  
  }

  ---

  I also tried to use process.BeginOutputReadLine() and wait for each frame in OutputDataReceived. But it returns parts of each frame, like the 10 first bytes, than other 50 bytes, it’s erratic.

  Is there any way to get the frames separately via the output stream ?