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• How can I simply replace the colors using the color masks on this image and then save it ? With RGBA channels as example

  31 août 2020, par karl-police

  So I got this GIF here :

  


  

  


  As you can see, it has Red, Green and Blue in it. And it also has a full transparency in it. This was composed together with FFMPEG out of images that looked exactly like that.

  


   

  


  Then, with FFMPEG I "decomposed" the RGB and Alpha channels using the filter "extractplanes".

  


  The gallery of that, in correct order starting from up to down, can be found here :

  


  https://imgur.com/a/WN0aGuW

  


  I am not sure if this actually helps me or if I'm supposed to decompose them. Because apperantly now, after decomposing them, I'm supposed to modify them, but I'm not really sure how. It's like how do I modify the red channel that only has black and white, so all at the end, will match to the specified HEX color that I want it to be to.

  


   

  


  Now, my question is. How do I exactly make the color changing happen ? Can I do this simply with JavaScript ? Is it possible to do with FFMPEG, if possible without ImageMagicks ? Maybe a programming language where not much installation is needed to do that ?

  


  What I understood is that. These channels basically contain values from 0 to 255 with black and white. I think the "brightness" is that what 0 and 255. So something inbetween, would be like grey.

  


  So basically, like we do (255,0,0) for red. In these channels, if I want red somewhere I need to put one fully white pixel on the red channel and on all the other channels, there has to be a fully black pixel.

  


  That's the concept. Now is the question, how can I do this ?

  


   

  


  At the end I want to make it look like the colors this one has, as example :

  


  

  


  This is from a game. So basically that's how it looks like in the game. And the game files only use these RGBA template sprites.

  


   

  


  I asked a similar question here : How to change colors of an image using RGBA and more channels independently of their color

  


  But somehow, I might didn't seem to explain it that well.

  


   

  


  I made a thing here to test around with things. I guess that's nearly close, but the lines are kinda weird. jsfiddle.net/qsgazubk

  


• 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.