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• OpenCV Encoding to H264 changing original RGB pixel values for gray images

  13 janvier 2020, par CristoJV

  I have the following issue :
  I’m creating a uniform gray color video (for testing) using OpenCV VideoWriter. The output video will reproduce a constant image where all the pixels must have the same value x (25, 51, 76,... and so on).
  When I generate the video using MJPG Encoder :

  vw = cv2.VideoWriter('./videos/input/gray1.mp4',
  
          cv2.VideoWriter_fourcc(*'MJPG'),
  
          fps,(resolution[1],resolution[0]))

  and read the output using the VideoCapture class, everything just works fine. I got a frame array with all pixel values set to (25,51,76 and so on).
  However when I generate the video using HEV1 (H.265) or also H264 :

  vw = cv2.VideoWriter('./videos/input/gray1.mp4',
  
          cv2.VideoWriter_fourcc(*'HEV1'),
  
          fps,(resolution[1],resolution[0]))

  I run into the following issue. The frame I got in BGR format follows the next configuration :

  • The blue channel value is the expected value (x) minus 4 (25-4=21, 51-4=47, 76-4=72, and so on).
  • The green channel is the expected value (x) minus 1 (25-1=24, 51-1=50, 76-1=75).
  • The red channel is the expected value (x) minus 3 (25-3=22, 51-3=48, 76-3=73).

  Notice that the value is reduced with a constant value of 4,1,3, independently of the pixel value (so there is a constant effect).
  What I could explain is a pixel value dependable feature, instead of a fixed one.
  What is worse is that if I choose to generate a video with frames consisting in every color (pixel values [255 0 0],[0 255 0] and [0 0 255]) I get the corresponding outputs values ([251 0 0],[0 254 0] and [0 0 252])
  I though that this relation was related to the grayscale Y value, where :

  Y = 76/256 * RED + 150/256 * GREEN + 29/256 * BLUE

  But this coefficients are not related with the output obtained. Maybe the problem is the reading with VideoCapture ?

  EDIT :
  In case that I want to have the same output value for the pixels (Ej : [10,10,10] experimentally I have to create a img where the red and blue channel has the green channel value plus 2 :

  value = 10
  
  img = np.zeros((resolution[0],resolution[1],3),dtype=np.uint8)+value
  
      img[:,:,2]=img[:,:,2]+2
  
      img[:,:,1]=img[:,:,1]+0
  
      img[:,:,0]=img[:,:,0]+2

  Anyone has experience this issue ? It is related to the encoding process or just that OpenCV treats the image differently, prior encoding, depending on the fourcc parameter value ?

• ffmpeg - trying to add a reversed section of original video to the back (boomerang effect)

  23 janvier 2020, par sn0ep

  I have a ffmpeg command as follows which basically scales the video down to 720p. Now i want to add a section to my command which will make a concatination of the video but in reverse. So that the video will also be in a loop like this :

  0s -> 10s -> 0s

  original command :

  ffmpeg -ss 0.0 -to 10.0 -i in.mp4 -filter_complex "fps=15,scale=720:-1" -y out.mp4

  Command after my edits :

  ffmpeg -ss 0.0 -to 10.0 -i in.mp4 -filter_complex "[0:v]fps=15,scale=720:-1,reverse,fifo[r];[0:v][r] concat=n=2:v=1 [v]" -map "[v]" -y out.mp4

  When executing im getting following erorrs :

  Parsed_concat_4 @ 0x7feb89d01d40] Input link in1:v0 parameters (size 720x1280, SAR 1:1) do not match the corresponding output link in0:v0 parameters (1080x1920, SAR 1:1)
  
  [Parsed_concat_4 @ 0x7feb89d01d40] Failed to configure output pad on Parsed_concat_4
  
  Error reinitializing filters!
  
  Failed to inject frame into filter network: Invalid argument
  
  Error while processing the decoded data for stream #0:1

  I’m very new into coding advanced ffmpeg commands.

• Why does javaFx run converted mp4 but not original ?

  20 février 2020, par brat

  Simply put, I have this issue where I have a mp4 file with a video. If I run it directly in the code posted here, the window opens but its white/blank. No movie showing.
  But if I run the original movie through ffmpeg it works.

  ffmpeg -i original.mp4 -s hd720 converted.mp4

  Note that Im converting from mp4 to mp4, I just change the size to hd720.
  So, the question is, why do I need to do that ?

  My code :

  package mypack;
  
  
  
  import javafx.application.Application;
  
  import javafx.scene.Group;
  
  import javafx.scene.Scene;
  
  import javafx.scene.layout.BorderPane;
  
  import javafx.scene.media.Media;
  
  import javafx.scene.media.MediaPlayer;
  
  import javafx.scene.media.MediaView;
  
  import javafx.stage.Stage;
  
  
  
  public class MyPlayer extends Application{
  
  
  
      public static void main(String[] args) {
  
          launch(args);
  
      }
  
  
  
  
  
      public void start(Stage primaryStage) throws Exception {
  
          BorderPane content = new BorderPane();
  
  
  
           Scene scene = new Scene(content, 540, 209);
  
           primaryStage.setScene(scene);
  
           primaryStage.setScene(scene);
  
  
  
           primaryStage.setTitle("Hello Media");
  
  
  
           String source;
  
           source = "file:///C:/Users/Noob/Desktop/Movies/original.mp4";
  
  //       source = "file:///C:/Users/Noob/Desktop/Movies/converted.mp4";
  
  
  
  
  
           Media media = new Media(source);
  
  
  
           MediaPlayer mediaPlayer = new MediaPlayer(media);
  
           mediaPlayer.setAutoPlay(true);
  
  
  
           MediaView mediaView = new MediaView(mediaPlayer);
  
           ((BorderPane) scene.getRoot()).getChildren().add(mediaView);
  
           primaryStage.show();
  
  
  
      }
  
  
  
  }

  For those audio/video afficionados/ffmpeg pros out there. This is what gets output from the original.

  ffprobe -i original.mp4

  ffprobe version 4.2.2 Copyright (c) 2007-2019 the FFmpeg developers
  
    built with gcc 9.2.1 (GCC) 20200122
  
    configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-amf --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt
  
    libavutil      56. 31.100 / 56. 31.100
  
    libavcodec     58. 54.100 / 58. 54.100
  
    libavformat    58. 29.100 / 58. 29.100
  
    libavdevice    58.  8.100 / 58.  8.100
  
    libavfilter     7. 57.100 /  7. 57.100
  
    libswscale      5.  5.100 /  5.  5.100
  
    libswresample   3.  5.100 /  3.  5.100
  
    libpostproc    55.  5.100 / 55.  5.100
  
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0000029bc02bc540] st: 0 edit list: 1 Missing key frame while searching for timestamp: 0
  
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0000029bc02bc540] st: 0 edit list 1 Cannot find an index entry before timestamp: 0.
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'original.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: mp42mp41
  
      creation_time   : 2020-02-18T17:09:21.000000Z
  
    Duration: 00:00:22.56, start: 0.000000, bitrate: 1631 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 3840x2160 [SAR 1:1 DAR 16:9], 1624 kb/s, 29.97 fps, 29.97 tbr, 29970 tbn, 59.94 tbc (default)
  
      Metadata:
  
        creation_time   : 2020-02-18T17:09:21.000000Z
  
        handler_name    : Mainconcept MP4 Video Media Handler
  
        encoder         : AVC Coding

  Could it have to do with size ? To big ? Since it sayes 3840x2160 in the original ? And Im making it smaller with hd720 ?
  If so, I would expect at least a corner of the movie showing, instead of a totally blank window.
  Im new at this, so if you also give some good link to ffmpeg (excluding official manpages) and/or a good tutorial/info page on video formatting pointed towards beginners it would be much appreciated. My understanding this far is there are containers which hold streams and each stream can have different codecs depending on the container.