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• Does ffmpeg support clip feature in ass with subtitle filter ?

  14 mars 2019, par neonew

  I want to use clip/iclip feature in ASS with ffmpeg to display the subtitles one by one. Below is my ASS file content :

  [Script Info]  
  
  ScriptType: v4.00+  
  
  WrapStyle: 0  
  
  ScaledBorderAndShadow: yes  
  
  PlayResX: 1000  
  
  PlayResY: 560  
  
  [V4+ Styles]  
  
  Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding  
  
  Style: Default,FZLanTingHei-R-GBK,24,&H000000,&H00FF0000,&H00000000,&H00000000,0,0,0,0,100,100,0,0,2,0,0,1,0,0,0,1  
  
  [Events]  
  
  Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text  
  
  Dialogue: 0,0:00:00.00,0:00:02.00,Default,,0000,0000,0000,,{\pos(717,91)\iclip(717,91,1000,191)\t(0,1000,\iclip(1000,91,1000,191))}Hello World!

  ffmpeg command :

  ffmpeg -i input.mp4 -filter_complex "subtitles=myass.ass" output.mp4

  However, the text just appeared two seconds, but didn’t have clip feature.
  So, is there something wrong ?

• Matlab VideoReader reading frames as green images or just not at all

  2 mai 2019, par Jordan

  I’m trying to read a video file and store the frames as a series of images. I’m using VideoReader but for some reason I’m having trouble. I want to store the frames of two videos encoded differently and measure the structural similarity and PSNR between the two on a frame-by-frame basis.

  Essentially I’ve three video files, an original (which reads fine), one compressed with VP9 using ffmpeg, and one compressed with H.624 using ffmpeg. The original video was originally just a set of frames merged into a .avi video using VirtualDub. The compressed videos are also .avi container.

  The VP9 video appeared to work fine but when I open the images using imshow() they appear to be just a solid green color. The video opens fine on VLC so I’m not sure what the problem is.

  The H.264 video doesn’t read at all. When it attempts to enter the "while hasFrame()" loop, it skips over it which leads to believe Matlab thinks the video frames aren’t there ? Again, this video opens fine in VLC and the three videos look almost identical.

  Anyone got any ideas why this is happening ? Is it to do with the way Matlab decodes the video or some parameters set by ffmpeg ?

  Original vs VP9 in Matlab

  Console output for ffmpeg - VP9

  Console output for ffmpeg - H264

  Main file :

  test_vid = 'vp9.avi';
  
  images = readVideos(test_vid);
  
  
  
  for i=1:length(images)
  
  
  
    % Convert from cells to matrices
  
    image1 = cell2mat(images(1,i));
  
    image2 = cell2mat(images(2,i));
  
  
  
    % Do stuff with the images here
  
  
  
    subplot(1,2,1);
  
    imshow(image1);
  
    subplot(1,2,2);
  
    imshow(image2);
  
  end

  ReadVideos() :

  function images = readVideos(test_video)
  
  
  
      % Video directories
  
      test_video_dir = strcat('src/', test_video);
  
      v_original = VideoReader('src/input.avi');
  
      v_test = VideoReader(test_video_dir);
  
  
  
      % Read original video
  
      i = 1;
  
      v_original.CurrentTime = 5;
  
      while hasFrame(v_original)
  
          frame = readFrame(v_original);
  
          originalImages{i} = frame;
  
          i = i + 1;
  
      end
  
  
  
      % Read test video
  
      i = 1;
  
      v_test.CurrentTime = 5;
  
      while hasFrame(v_test)
  
           frame = readFrame(v_test);
  
           testImages{i} = frame;
  
           i = i + 1;
  
      end
  
  
  
      images = cat(1, originalImages, testImages);
  
  end

  On a side note, is Matlab the best choice for the task or is there specialised software out there for doing this ?

• ffmpeg to calculate audio/visual difference between compressed and non-compressed video

  14 juin 2019, par Asymetr

  I’m trying to calculate the audio + visual difference between a harshly compressed video file and one that hasn’t been.
  I’m using pipes because ultimately I wish this to take src from a camera stream.

  I’ve managed to get the video results that I’m looking for, but I’m struggling with the audio.
  I’ve added a line to invert the phase of the compressed audio, so that when they add up in the blend they should almost cancel each other out, but that doesn’t happen.

  ffmpeg -i input.avi -f avi -c:v libxvid -qscale:v 30 -c:a wmav1 - | \
  
  ffmpeg -i - -f avi -af "aeval='-val(0)':c=same" - | \
  
  ffmpeg -i input.avi -i - -filter_complex "blend=all_mode=difference" -c:v libx264 -crf 18 -f avi - | \
  
  ffplay -

  I can still hear all the audio, when what I should be hearing are solely compression artifacts. thx