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• Why does ffmpeg never finish when converting a video from my web app ?

  30 septembre 2011, par Mike

  I am trying to convert a video when the user submits a form. It seems to convert ok but the file "is being used by another proccess" when I try to do anything with it. It looks like ffmpeg.exe never exits. My code is below is there anything I should be doing different to allow the process to release the file ? If I run this manually it exits fine.

  internal class ConversionUtility : Utility
  
  {
  
      public void Convert(string videoFileName)
  
      {
  
          var video = new VideoFile(videoFileName);
  
  
  
          if (!video.infoGathered)
  
              GetVideoInfo(video);
  
  
  
          var Params = string.Format("-y -i \"{0}\" -coder ac -me_method full -me_range 16 -subq 5 -sc_threshold 40 -vcodec libx264 -cmp +chroma -partitions +parti4x4+partp8x8+partb8x8 -i_qfactor 0.71 -keyint_min 25 -b_strategy 1 -g 250 -r 20 \"{1}\"", video.Path, Path.ChangeExtension(videoFileName,".mp4"));
  
          //var Params = string.Format("-y -i \"{0}\" -acodec libfaac -ar 44100 -ab 96k -coder ac -me_method full -me_range 16 -subq 5 -sc_threshold 40 -vcodec libx264 -s 1280x544 -b 1600k -cmp +chroma -partitions +parti4x4+partp8x8+partb8x8 -i_qfactor 0.71 -keyint_min 25 -b_strategy 1 -g 250 -r 20 c:\\output3.mp4", video.Path, videoFileName);
  
          //var Params = String.Format(" {0} \"{1}\"",this.FFmpegLocation, video.Path);
  
  
  
          var threadStart = new ParameterizedThreadStart(del => RunProcess(Params));
  
          var thread = new Thread(threadStart);
  
          thread.Start();            
  
          //RunProcess(Params);
  
      }
  
  }
  
  
  
  internal class Utility
  
  {
  
      public string FFmpegLocation { get; set; }        
  
      private string WorkingPath { get { return Path.GetDirectoryName(FFmpegLocation); } }
  
  
  
      protected string RunProcess(string Parameters)
  
      {
  
          //create a process info
  
          var oInfo = new ProcessStartInfo(this.FFmpegLocation, Parameters)
  
          {
  
              UseShellExecute = false,
  
              CreateNoWindow = true,
  
              RedirectStandardOutput = true,
  
              RedirectStandardError = true
  
          };
  
  
  
          //Create the output and streamreader to get the output
  
          string output = null; StreamReader srOutput = null;
  
  
  
          //try the process
  
          try
  
          {
  
              //run the process
  
              Process proc = System.Diagnostics.Process.Start(oInfo);
  
  
  
              proc.WaitForExit();
  
              //if (!proc.WaitForExit(10000))
  
              //    proc.Kill();
  
  
  
  
  
              //get the output
  
              srOutput = proc.StandardError;
  
  
  
              //now put it in a string
  
              output = srOutput.ReadToEnd();
  
  
  
              proc.Close();
  
          }
  
          catch (Exception)
  
          {
  
              output = string.Empty;
  
          }
  
          finally
  
          {
  
              //now, if we succeded, close out the streamreader
  
              if (srOutput != null)
  
              {
  
                  srOutput.Close();
  
                  srOutput.Dispose();
  
              }
  
          }
  
          return output;
  
      }

• FFMPEG : chroma key / greenscreen filter for images / video

  6 septembre 2016, par Daniel Ruf

  I need for a video to use chroma key filter / greenscreen filter and overlay it over another video and output it as new video.

  Are there any existing libraries, scripts, filters or solutions for this purpose ?

• Stream video from ffmpeg and capture with OpenCV

  10 décembre 2014, par chembrad

  I have a video stream coming in on rtp to ffmpeg and I want to pipe this to my OpenCV tools for live streaming processing. The rtp linkage is working because I am able to send the incoming data to a file and play it (or play if via ffplay). My OpenCV implementation is functional as well because I am able to capture video from a file and also a webcam.

  The problem is the streaming to OpenCV. I have heard that this may be done using a named pipe. First I could stream the ffmpeg output to the pipe and then have OpenCV open this pipe and begin processing.

  What I’ve tried :

  I make a named-pipe in my cygwin bash by :

      $ mkfifo stream_pipe

  Next I use my ffmpeg command to pull the stream from rtp and send it to the pipe :

      $ ffmpeg -f avi -i rtp://xxx.xxx.xxx.xxx:1234 -f avi -y out.avi > stream_pipe

  I am not sure if this is the right way to go about sending the stream to the named pipe but it seems to be accepting the command and work because of the output from ffmpeg gives me bitrates, fps, and such.

  Next I use the named pipe in my OpenCV capture function :

      $ ./cvcap.exe stream_pipe

  where the code for cvcap.cpp boils down to this :

      cv::VideoCapture *pIns = new cv::VideoCapture(argv[1]);

  The program seems to hang when reaching this one line, so, I am wondering if this is the right way of going about this. I have never used named pipes before and I am not sure if this is the correct usage. In addition, I don’t know if I need to handle the named pipe differently in OpenCV—change code around to accept this kind of input. Like I said, my code already accepts files and camera inputs, I am just hung up on a stream coming in. I have only heard that named pipes can be used for OpenCV—I haven’t seen any actual code or commands !

  Any help or insights are appreciated !

  UPDATE :

  I believe named pipes may not be working in the way I intended. As seen on this cygwin forum post :

  The problem is that Cygwin’s implementation of fifos is very buggy. I wouldn’t recommend using fifos for anything but the simplest of applications.

  I may need to find another way to do this. I have tried to pipe the ffmpeg output into a normal file and then have OpenCV read it at the same time. This works to some extent, but I imagine in can be dangerous to read and write from a file concurrently—who knows what would happen !