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• How to use the function expr in drawtext ffmpeg to add a text to video ?

  18 décembre 2013, par nhanpt

  I'm try to add a text to my video using FFmpeg.
  Sources : http://www.ffmpeg.org/ffmpeg-all.html#drawtext-1

  ffmpeg -i 1385363109.avi -vf "drawtext=fontfile=/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans.ttf : text = %{localtime}: \x=(w-tw)/2: y=h-(2*lh): fontcolor=white: box=1: boxcolor=0x00000000@1" -an -y out11.avi

  I am trying to figure out how to add a timestamp in a formatable manner (specifically, I'd like to show mm:ss). I think this should be possible using a command like

  Code : Select all
  ffmpeg -i input.avi -vf "drawtext=fontfile=/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans-Bold.ttf:expansion=normal:text='%expr=floor(t/60)~:%expr=floor(t)' : fontcolor=white " output.avi

  But I just get a lot of

  Code : Select all
  [Parsed_drawtext_0 @ 0x1a68a80] %expr=floor(t/60) is not known

  and no text is displayed.

  If I try

  Code : Select all
  ffmpeg -i input.avi -vf "drawtext=fontfile=/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans-Bold.ttf:expansion=normal:text='%expr' : fontcolor=white " output.avi

  I get instead

  Code : Select all
  [Parsed_drawtext_0 @ 0x2d22be0] %expr requires at least 1 arguments

  so the version of drawtext I have definitely recognizes the expr function, but I can't figure out the syntax for giving it an argument. Does anyone know what the synatax is for the expr (or e) function ?

  Alternately, if there is another way to display the timecode as mm:ss that would be great too. I know that using the 'timecode' argument of drawtext you can get hh:mm:ss:ff, or using text='%pts' gives me decimal seconds to the microsecond, but I am sure that my advisor (who is very picky) will not accept either of these. Thanks in advance for any assistance !

• 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.

• 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.