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• Evaluate function within ffmpeg drawtext

  22 juin 2022, par Dan Steingart

  I am looking to display a counter that is a multiple of the frame number on a video created with ffmpeg. Previous answers on SO taught me that a command of the form

  


  ffmpeg -y -r 25  -pattern_type glob -i '*.jpg' -vf "text='%{n}': start_number=0: x=0: y=0: fontcolor=black: fontsize=30: box=1: boxcolor=white: boxborderw=5" -c:a copy movie.mp4


  


  Will display the frame number, and this works nicely. But if I try to evaluate an expression within the %{}, e.g.

  


  ffmpeg -y -r 25  -pattern_type glob -i '*.jpg' -vf "text='%{n*50}': start_number=0: x=0: y=0: fontcolor=black: fontsize=30: box=1: boxcolor=white: boxborderw=5" -c:a copy movie.mp4


  


  Then I get the following error

  


  [Parsed_drawtext_0 @ 0x55683f9b00] %{n*50} is not known    


  


  on each frame. What is the proper syntax to evaluate n*50 and display in drawtext ? TIA.

  


• 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.

• How to find higest bitrate in mp4 file and extract jpg ?

  10 octobre 2018, par Igor Petev

  I im using ffmpeg and have mp4 file that is in size around 50MB and duration 2m7sec.I need to write batch script for windows that will read whole mp4 file find position in seconds where higest bitrate is there and extract jpg image from that position.

  For example, i have mp4 trailer file that i would like to extract cover, using above script where i define time to extract jpg i get on some mp4 trailers black screen...so using above idea to find higet bitrate for shure will not be black screen, will be picture of some scene.

  Here is windows batch code that extract jpg dfrom mp4 using user defined time :

  @ECHO OFF
  
  SET oldName=
  
  SET newName=
  
  
  
  FOR %%A IN (*.mp4) DO (
  
  SET oldName=%%A
  
  SET newName=%%A
  
  CALL :MAKEJPG
  
  )
  
  
  
  :MAKEJPG
  
  SET newName=%newName:mp4=jpg%
  
  IF NOT EXIST %newName% (
  
  START /B /WAIT D:\www\ffmpeg.exe -i "%oldName%" -ss 00:00:17.30 -vcodec mjpeg -vframes 1 -f image2 "%newName%"
  
  EXIT
  
  )