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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.

• How can I quantitatively measure gstreamer H264 latency between source and display ?

  10 août 2018, par KevinM

  I have a project where we are using gstreamer , x264, etc, to multicast a video stream over a local network to multiple receivers (dedicated computers attached to monitors). We’re using gstreamer on both the video source (camera) systems and the display monitors.

  We’re using RTP, payload 96, and libx264 to encode the video stream (no audio).

  But now I need to quantify the latency between (as close as possible to) frame acquisition and display.

  Does anyone have suggestions that use the existing software ?

  Ideally I’d like to be able to run the testing software for a few hours to generate enough statistics to quantify the system. Meaning that I can’t do one-off tests like point the source camera at the receiving display monitor displaying a high resolution and manually calculate the difference...

  I do realise that using a pure software-only solution, I will not be able to quantify the video acquisition delay (i.e. CCD to framebuffer).

  I can arrange that the system clocks on the source and display systems are synchronised to a high accuracy (using PTP), so I will be able to trust the system clocks (else I will use some software to track the difference between the system clocks and remove this from the test results).

  In case it helps, the project applications are written in C++, so I can use C event callbacks, if they’re available, to consider embedding system time in a custom header (e.g. frame xyz, encoded at time TTT - and use the same information on the receiver to calculate a difference).

• FFMPEG video encoding time increases over time

  8 août 2018, par NStof

  I am creating a fairly basic DVR in C# using the FFMPEG wrapper in Accord.net. Essentially it works by getting the raw frames from the on-board frame grabber, displays the frame on screen and places it in a buffer. In a Separate thread in 20 second intervals, the frames are taken from the buffer and using Accord.Video.FFMPEG.VideoFileWriter.WriteVideoFrame(Bitmap bmp) the frame is encoded and saved to disk. Video is saved in two minute file chunks.
  This works happily for about 24-30 hours, however after that it looks like the average time it takes to encode/save each frame increases to the point where it gets new frames faster than they can be saved. This causes buffer to grow and ends in tears.

  What I would like to know is why does the time it takes to complete the WriteVideoFrame(Bitmap bmp) function increase over time.

  What I think I know so far :
  I do not know if this problem is caused by something in FFMPEG or in the Accord.net wrapper.
  I am reasonably sure it is not caused by hardware. Neither CPU usage nor HDD are working particularly hard. In fact, when I monitor the CPU usage, it does not work any harder or less hard when the encoding time increases.
  When I stop recording (close and dispose all Accord.net objects) and start again, it does not reset the encoding speed. Only when I close the software and start it again does it fix the problem.
  Any thoughts and help with this will be greatly appreciated. If more information is required, please let me know.