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• FFMPEG Replacing black color fragments with alpha channel transparency

  31 décembre 2017, par kostya572

  I have file.mov video. It has a lot of blank black color fragments that have different durations.

  I need to replace black color fragments that show up for more than 5 seconds with transparency. Is that possible to add some alpha channel for that purpose ?

  Comment to Mulvya’s answer :

  Amazing solution. With #2 section everything ok.

  With #1 section I created this code :

  output=$(ffprobe -f lavfi -i "movie=file.mov,blackdetect=d=3.5" -show_entries tags=lavfi.black_start,lavfi.black_end -of compact=p=0 -v 0|awk '!/^$/')
  
  echo $output

  using awk '!/^$/' to remove empty lines.

  Here is the output I get :

  

  tag:lavfi.black_start repeats with same value several times, not having right structure with closing tag:lavfi.black_end

  If I change blackdetect=d=3.5 to other value, for exaple d=10, it outputs the same result as d=3.5. How could I solve this issue having right tag:lavfi.black_start,tag:lavfi.black_end synthax with correct grepping d= value ?

• FFMPEG Determine average color of an area of a video

  12 novembre 2019, par Naved Khan

  I have a use case where I’d want to insert one of two watermarks - one designed for a dark-ish background, the other for a light background into a video. Let’s say that I’d want to do this on the top right corner of the video.

  How do I determine the average color of the top right section of the video ? Post this, how do I determine which watermark to use by looking at the average color ?

  I have a solution right now where I am taking equally spaced screenshots and then measuring the average color, but it’s excruciatingly slow, especially for longer videos.

  # Calculate average color
  
      black_distances = []
  
      white_distances = []
  
  
  
      movie = FFMPEG::Movie.new(video_file)
  
      (0..movie.duration / 10).each do |second|
  
  
  
        # extract a frame
  
        filename = "tmp/watermark/#{SecureRandom.uuid}.jpg"
  
        movie.screenshot filename.to_s, seek_time: second
  
  
  
        # analyse frame for color distance
  
        frame = MiniMagick::Image.open(filename)
  
        frame.crop('20%x20%+80%+0')
  
        frame.resize('1x1')
  
        pixel = frame.get_pixels.flatten
  
  
  
        distance_from_black = Math.sqrt(((black[0] - pixel[0])**2 + (black[1] - pixel[1])**2 + (black[2] - pixel[2])**2))
  
        distance_from_white = Math.sqrt(((white[0] - pixel[0])**2 + (white[1] - pixel[1])**2 + (white[2] - pixel[2])**2))
  
  
  
        black_distances.push distance_from_black
  
        white_distances.push distance_from_white
  
  
  
        File.delete(filename) if File.exist?(filename)
  
      end
  
  
  
      average_black_distance = black_distances.reduce(:+).to_f / black_distances.size
  
      average_white_distance = white_distances.reduce(:+).to_f / white_distances.size

  I am also confused about how to use the resulting average_black_distance and average_white_distance to determine which watermark to use.

• FFMPEG Wrong color space with ProRes 4444 [closed]

  6 février 2020, par Mirza Kadic

  I’m unable to convert a video with ffmpeg in codec ProRes 4444 without color shift (something to do with colorspace). If I do quicktime png, color space stays the same, no problems with that.
  The only thing that fixes this is -vf colormatrix=bt601:bt709, but then I loose alpha channel, which I need of course.
  Any help would be appreciated.