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• C# get dominant color in an image

  22 janvier 2017, par CK13

  I’m building a program that makes screenshots from a video.
  It extracts frames from the video (with ffmpeg) and then combines them into one file.

  All works fine, except sometimes I get (almost) black images, mostly in the beginning and ending of the video.

  A possible solution I can think of is to detect if the extracted frame is dark. If it is dark, extract another frame from a slightly different time.

  How can I detect if the extracted frame is dark/black ? Or is there another way I can solve this ?

  private void getScreenshots_Click(object sender, EventArgs e)
  
  {
  
      int index = 0;
  
      foreach (string value in this.filesList.Items)
  
      {
  
          string file = selectedFiles[index] + "\\" + value;
  
  
  
          // ------------------------------------------------
  
          //   MediaInfo
  
          // ------------------------------------------------
  
          // https://github.com/Nicholi/MediaInfoDotNet
  
          //
  
          // get file width, height, and frame count
  
          //
  
          // get aspect ratio of the video
  
          // and calculate height of thumbnail 
  
          // using width and aspect ratio
  
          //
  
          MediaInfo MI = new MediaInfo();
  
          MI.Open(file);
  
          var width = MI.Get(StreamKind.Video, 0, "Width");
  
          var height = MI.Get(StreamKind.Video, 0, "Height");
  
          decimal d = Decimal.Parse(MI.Get(StreamKind.Video, 0, "Duration"));
  
          decimal frameCount = Decimal.Parse(MI.Get(StreamKind.Video, 0, "FrameCount"));
  
          MI.Close();
  
          decimal ratio = Decimal.Divide(Decimal.Parse(width), Decimal.Parse(height));
  
          int newHeight = Decimal.ToInt32(Decimal.Divide(newWidth, ratio));
  
          decimal startTime = Decimal.Divide(d, totalImages);
  
          //totalImages - number of thumbnails the final image will have
  
          for (int x = 0; x < totalImages; x++)
  
          {
  
              // increase the time where the thumbnail is taken on each iteration
  
              decimal newTime = Decimal.Multiply(startTime, x);
  
              string time = TimeSpan.FromMilliseconds(double.Parse(newTime.ToString())).ToString(@"hh\:mm\:ss");
  
  
  
              string outputFile = this.tmpPath + "img-" + index + x + ".jpg";
  
  
  
              // create individual thumbnails with ffmpeg
  
              proc = new Process();
  
              proc.StartInfo.FileName = "ffmpeg.exe";
  
              proc.StartInfo.Arguments = "-y -seek_timestamp 1 -ss " + time + " -i \"" + file + "\" -frames:v 1 -qscale:v 3 \"" + outputFile + "\"";
  
              proc.Start();
  
              proc.WaitForExit();
  
          }
  
  
  
          // set width and height of final image
  
          int w = (this.cols * newWidth) + (this.spacing * this.cols + this.spacing);
  
          int h = (this.rows * newHeight) + (this.spacing * this.rows + this.spacing);
  
  
  
          int left, top, i = 0;
  
          // combine individual thumbnails into one image
  
          using (Bitmap bmp = new Bitmap(w, h))
  
          {
  
              using (Graphics g = Graphics.FromImage(bmp))
  
              {
  
                  g.Clear(this.backgroundColor);
  
                  // this.rows - number of rows
  
                  for (int y = 0; y < this.rows; y++)
  
                  {
  
                      // put images on a column
  
                      // this.cols - number of columns
  
                      // when x = number of columns go to next row
  
                      for (int x = 0; x < this.cols; x++)
  
                      {
  
                          Image imgFromFile = Image.FromFile(this.tmpPath + "img-" + index + i + ".jpg");
  
                          MemoryStream imgFromStream = new MemoryStream();
  
                          imgFromFile.Save(imgFromStream, imgFromFile.RawFormat);
  
                          imgFromFile.Dispose();
  
  
  
                          left = (x * newWidth) + ((x + 1) * this.spacing);
  
                          top = (this.spacing * (y + 1)) + (newHeight * y);
  
                          g.DrawImage(Image.FromStream(imgFromStream), left, top, newWidth, newHeight);
  
                          i++;
  
                      }
  
                  }
  
              }
  
  
  
              // save the final image
  
              bmp.Save(selectedFiles[index] + "\\" + value + ".jpg");
  
          }
  
          index++;
  
      }
  
  }

• Getting log line for each extracted frame from FFMPEG

  3 février 2016, par wpfwannabe

  I am using FFMPEG.exe to extract frames from various videos. As this is a programmatic solution and getting the total frame count and/or duration can prove tricky (with ffprobe), I am thinking I could use the console output to detect individual frames’ timestamps but I am getting a single output line every N frames like this :

  frame=   20 fps=0.0 q=0.0 size=       0kB time=00:00:01.72 bitrate=   0.0kbits/s
  
  frame=   40 fps= 38 q=0.0 size=       0kB time=00:00:04.02 bitrate=   0.0kbits/s
  
  frame=   60 fps= 39 q=0.0 size=       0kB time=00:00:06.14 bitrate=   0.0kbits/s
  
  frame=   70 fps= 38 q=0.0 Lsize=       0kB time=00:00:07.86 bitrate=   0.0kbits/s

  Is there a command line option to force output for each and every frame ? If so, I could extract the time= portion. This is the command line currently used :

  ffmpeg.exe -i video.avi -y -threads 0 -vsync 2 %10d.jpeg

  Ideally, replacing %10d.jpeg with some other format that writes frame’s timestamp but I don’t think this exists.

• Recording application output to video using FFmpeg (or similar)

  15 décembre 2011, par John

  We have a requirement to lets users record a video of our 3D application. I can already grab the individual rendered frames so this question is specifically about how to write frames into a video file.

  I don't think writing each frame as a separate file and post-processing is a workable option.

  I can look at options to record to a simple video file for later optimising/encoding, or writing directly to a sensibly encoded format.

  FFmpeg was suggested in another post but it looks a bit daunting to me. Is it the best option, if not what can be suggested ? We can work with LGPL but not full GPL.

  We're working on Windows (Win32 not MFC) in C++. Sample/pseudo code with your recommended library is very much appreciated... basically after how to do 3 functions :

  • startRecording() does whatever initialization is needed
  • recordFrame() takes pointer to frame data and encodes it, ideally with timing data
  • endRecording() finalizes the video file, shuts down video system, etc