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• Overlaying one video on another one, and making black pixels transparent

  25 janvier 2023, par Michael A

  I'm trying to use FFMPEG to create a video with one video overlayed on top another.

  



  I have 2 MP4s. I need to make all BLACK pixels in the overlay video transparent so that I can see the main video underneath it.

  



  I found two ways to overlay one video on another :

  



  First, the following positions the overlay in the center, and therefore, hides that portion of the main video beneath it :

  



      ffmpeg -i 1.mp4 -vf "movie=2.mp4 [a]; [in][a] overlay=352:0 [b]" combined.mp4 -y


  



  And, this one, places the overlay video on the left, but it's opacity is set to 50% so at least other one beneath it is visible :

  



  ffmpeg -i 1.mp4 -i 2.mp4 -filter_complex "[0:v]setpts=PTS-STARTPTS[top]; [1:v]setpts=PTS-STARTPTS, format=yuva420p,colorchannelmixer=aa=0.5[bottom]; [top][bottom]overlay=shortest=0" -acodec libvo_aacenc -vcodec libx264 out.mp4 -y


  



  My goal is simply to make all black pixels in the overlay (2.mp4) completely transparent. How can this be done.

  


• Change gray pixel to black pixels in video

  12 janvier 2023, par yabru

  I want to change every gray pixel in my video with the (r,g,b) 158,158,158 to black 0,0,0

  


  I've tried the solution of THIS post, but backwards. I just do not understand the syntax.

  


  ffmpeg -y -I my_video.mp4 -c copy -c:v libx264 -preset ultrafast -vf "yadif,format=rgb24, lutrgb=r='if(eq(val,158),0,val)':g='if(eq(val,158),0,val)':b='if(eq(val,158),0,val)'" my_video_fixed.mp4

  


  ^ doesn't change anything

  


  could anyone help me modify my command (with an explanation of the solution) :)

  


  version : ffmpeg version 5.1.2

  


• Is ffmpeg's chromakey filter broken when matching black/white ?

  7 janvier 2023, par Taylor Brown

  I have a file, colors.png. It looks like this :

  



  Let's say I want to make the red square transparent. When I run ffmpeg -i colors.png -filter_complex "[0]chromakey=0xff0000:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-red.png (notice I use similarity=0.1 to make this work), I get exactly that :

  



  How about making the blue square transparent ? ffmpeg -i colors.png -filter_complex "[0]chromakey=0x0000ff:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-blue.png works too !

  



  But what about replacing black ? ffmpeg -i colors.png -filter_complex "[0]chromakey=0x000000:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-black.png gives me this :

  



  And likewise, replacing white with ffmpeg -i colors.png -filter_complex "[0]chromakey=0xffffff:similarity=0.1:blend=0.0[out]" -map "[out]" colors-rm-white.png gives me the same result :

  



  Why is this ? Even if I use similarity=0.01, which according to the docs "matches only the exact key color", this still doesn't work when I'm trying to make black/white transparent. Is ffmpeg broken, or am I misunderstanding the chromakey filter ?