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• FFmpeg compose, multi layers and filters, need kindly help 

  9 octobre 2019, par jadeshohy

  Pretty new to FFmpeg. We would like to use FFmpeg as a important part of an AR project.

  Currently, we find it is not easy for us.

  We want to compose the footages with FFmpeg.

  We got 5 layers, wanted to blend them with specific mode, like the things in After Effects.

  • layer-1/ [A.webm] video，vp9 codec, which has a transparent BG,has to be added as [normal mode]

  • layer-2/ [B.mp4] video, optical-flare things with black BG,has to be added as [screen mode]

  • layer-3/ [C.mp4] video, some motion graphic things with light BG,has to be added as [overlay mode]

  • layer-4/ [BG.MP4], backgound things, has to be added as [normal mode]

  After we blend those 4 (like pre-compose,use blend filter), we want to add another layer-5/[icon.png] which is the special icon.

  Layer-5 need to overlay the pre-compose. We have to overlay it at the special position (use overlay filter ?).

  Cause [icon.png] may change frequently. we want to deal with that after the 4 layer blending.

  But at the first step, when we set normal mode for layer-1 in blend filter, layer-1 [A.webm] lost the transparent BG，it gave us a black BG which block all other things.
  Blend filter can not handle the alpha channel of vp9 webm ?
  When we set the mode of layer-1 to screen mode,the translucent thing was not what we need.

  Could you please give us some commands to achieve the blend above ?

  The commands that are really work will be extremely useful for our FFmpeg initiation.

• Overlay video with alpha using FFmpeg on macOS Catalina... problems

  16 octobre 2019, par jogga

  In previous versions of macOS (10.14 Mojave and older) I used FFmpeg to overlay a video with alpha on top of another video with much success. Now when updated to macOS Catalina the same FFmpeg commands suddenly doesn’t work. It just produces black where the transparency should have been according to the alpha channel. The video I overlay on top is a ProRes 4444 file (which includes an alpha channel) and it no longer works as expected.

  I have tried several versions of FFmpeg from the nightly builds to the latest stable one (version 4.2.1) to no avail. Nothing works :-(

  The simplest form of the command I have been using looks like this :

  ffmpeg -y -i skiing.mp4 -i subtitles.ap4h -filter_complex overlay subtitled.m4v 

  Doesn’t work. But if I replace the subtitles.ap4h file with a simple .png image with alpha, it works ?

  I have also been experimenting with the blend filter, but I really don’t understand the gist of it yet.

  Can someone please shed some light on this. Have anyone else out there seen this problem.

  Do you have any suggestions on how to use the blend filter instead of the overlay filter to accomplish the same task ?

  You can find the sample files I used in my dropbox...

  https://www.dropbox.com/s/8z3grpsbejb1na0/skiing.mp4?dl=0
  https://www.dropbox.com/s/8c79lg07rbuqyhn/subtitles.ap4h?dl=0

  Really looking forward to someone help me solve this mystery.

  Best regards / Jörgen

• 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.