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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++;
  
      }
  
  }

• Difference between 'display_aspect_ratio' and 'sample_aspect_ratio' in ffprobe [duplicate]

  18 juin 2018, par John Allard

  This question already has an answer here :

  • ffmpeg scaling not working for video
    
    1 answer
    

  I have an issue where a video is played in the correct 16:9 aspect ratio when played through VLC or quicktime player, but when I attempt to extract individual frames with ffmpeg the frames come out as 4:3 aspect ratio.

  The ffprobe output on the video in question is as follows

  $ ffprobe -v error -select_streams v:0 -show_entries stream -of default=noprint_wrappers=1 -print_format json movie.mp4
  
  
  
  {
  
  "programs": [
  
  
  
  ],
  
  "streams": [
  
      {
  
          "index": 0,
  
          "codec_name": "h264",
  
          "codec_long_name": "H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
  
          "profile": "Main",
  
          "codec_type": "video",
  
          "codec_time_base": "126669/6400000",
  
          "codec_tag_string": "avc1",
  
          "codec_tag": "0x31637661",
  
          "width": 2592,
  
          "height": 1944,
  
          "coded_width": 2592,
  
          "coded_height": 1944,
  
          "has_b_frames": 0,
  
          "sample_aspect_ratio": "4:3",
  
          "display_aspect_ratio": "16:9",
  
          "pix_fmt": "yuvj420p",
  
          "level": 50,
  
          "color_range": "pc",
  
          "color_space": "bt709",
  
          "color_transfer": "bt709",
  
          "color_primaries": "bt709",
  
          "chroma_location": "left",
  
          "refs": 1,
  
          "is_avc": "true",
  
          "nal_length_size": "4",
  
          "r_frame_rate": "25/1",
  
          "avg_frame_rate": "3200000/126669",
  
          "time_base": "1/12800",
  
          "start_pts": 0,
  
          "start_time": "0.000000",
  
          "duration_ts": 126682,
  
          "duration": "9.897031",
  
          "bit_rate": "4638928",
  
          "bits_per_raw_sample": "8",
  
          "nb_frames": "250",
  
          "disposition": {
  
              "default": 1,
  
              "dub": 0,
  
              "original": 0,
  
              "comment": 0,
  
              "lyrics": 0,
  
              "karaoke": 0,
  
              "forced": 0,
  
              "hearing_impaired": 0,
  
              "visual_impaired": 0,
  
              "clean_effects": 0,
  
              "attached_pic": 0,
  
              "timed_thumbnails": 0
  
          },
  
          "tags": {
  
              "language": "und",
  
              "handler_name": "VideoHandler"
  
          }
  
      }
  
  ]
  
  }

  So it says

      "width": 2592,
  
      "height": 1944,
  
      "coded_width": 2592,
  
      "coded_height": 1944,
  
      "has_b_frames": 0,
  
      "sample_aspect_ratio": "4:3",
  
      "display_aspect_ratio": "16:9",

  which seems odd to me. The width/height are in 4:3, the sample aspect ratio is 4:3, the display is 16:9 ?

  Now, when I play this through VLC/Quicktime the video looks fine (screenshot below)

  

  but now, if I run an ffmpeg command to extract individual frames from this video, they come out in 4:3

  ffmpeg -y -hide_banner -nostats -loglevel error -i movie.mp4 -vf select='eq(n\,10)+eq(n\,20)+eq(n\,30)+eq(n\,40)',scale=-1:640 -vsync 0 /tmp/ffmpeg_image_%04d.jpg

  

  So I guess my questions are as follows :

  1. what is the relation between display aspect ratio, sample aspect ratio, and the width/height ratio ?
  2. how to I get ffmpeg to output in the correct aspect ratio ?

• ffmpeg - split video into multiple parts with different duration

  16 avril 2023, par Pierrou

  in order to split very old episodes from my VHS rips, I would like to split video files into multiple parts according to timestamps in csv file :

  


  file1;00:01:13.280;00:14:22.800;Part 1
file1;00:14:41.120;00:26:05.400;Part 2
file1;00:26:23.680;00:39:41.720;Part 3
file1;00:40:00.000;00:51:43.280;Part 4
file1;00:53:50.200;01:06:15.680;Part 5
file1;01:06:33.960;01:20:58.400;Part 6
file1;01:21:16.680;01:34:57.320;Part 7
file1;01:35:15.600;01:48:21.640;Part 8
file1;01:49:15.160;01:51:54.720;Part 9
file2;00:01:13.280;00:13:30.960;Part 1
file2;00:13:49.240;00:29:04.240;Part 2
file2;00:29:22.520;00:43:24.080;Part 3
file2;00:43:42.360;00:58:12.560;Part 4
file2;01:00:03.880;01:12:52.840;Part 5
file2;01:13:11.120;01:24:13.280;Part 6
file2;01:24:31.560;01:51:12.720;Part 7
file2;01:52:06.840;01:54:55.640;Part 8


  


  So how can I have multiple lines like those ?

  


  ffmpeg -i file1.avi -c copy -ss 00:01:13.280 -to 00:14:22.800 file1/part1.avi


  


  So I would like to keep each parts in individual files and remove everything else.