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• Remove Static Pixels from a Video to Mimic a Green Screen Effect [closed]

  2 août 2021, par nKrkan

  I have a video that's 50 seconds in length, resolution of 480x480 and 16 frames per second.

  


  There is a person talking in it, with the background being static I thought if there's a way
  
to remove those static pixels (background) and just extract the moving pixels (foreground)
  
and possibly mimic a green screen effect ?

  


  I was thinking on writing a picture-by-picture comparison tool to do such thing but I don't
  
believe I'm up to the task, or maybe It's laziness.

  


  And now I know, some of you will point out that the video has compression artifacts and that
  
might cause some problems but It doesn't have to be Studio quality stuff.

  


  I tried the ffmpeg command from this question : Remove random background from video using ffmpeg or Python
  
And it does mask the person, but... I couldn't quite get it to work, apparently putting the
  
reference image in the input makes that image burned into the video, thus having no way to
  
remove it, but it did mask the background as black and the person as greenish, so still not a
  
viable way to do it.

  


  Have also tried some Python projects I've found on the GitHub but none of them worked as
  
I expected.

  


  So, what I thought to do is simply compare the first and the second frame of the video, check
  
all the pixels by comparing them with the two sources, and change those that stay within a
  
certain range of the initial pixel value.

  


  I should point out I'm not very knowledgeable with mathematics and the majority of the
  
methods used in these type of things, but perhaps someone could point me to an interesting
  
source to read and learn, or by providing an alternative to the methods aforementioned above.

  


• FFmpeg - Rotating at angle

  23 septembre 2017, par connor

  I’ve been working through FFmpeg, but I have been unable to get a rotation to run from the examples they have on their site. I am trying to "wiggle" a video back and forth at a fixed point on the bottom - think a head moving left to right (and so on).

  I am attempting to do this with the filter "rotate" (https://ffmpeg.org/ffmpeg-filters.html#rotate). Attempting to use their examples, I get an error.

  This is what I have so far :

  ffmpeg -i vid1.mp4 -i vid2.mov -loop 1 -i image.png -filter_complex "\
  
      [2:v]alphaextract, scale=240x160[mask];\
  
      [0:v] scale=240x160, rotate=A*sin(2*PI/T*t) [ascaled];\
  
      [ascaled][mask]alphamerge[masked];\
  
      [1:v]scale=480x360[background];\
  
      [background][masked]overlay=120:20"\
  
      -c:a copy 65B6354F61B4AF02_HD_sq.MOV

  I am using "rotate" directly from an example in an attempt to get something to run at all.

  The error I get back is :

  [Parsed_rotate_3 @ 0x7ff4476045e0] [Eval @ 0x7fff5b3e3f00] Undefined constant or missing '(' in 'T*t)'
  
  [Parsed_rotate_3 @ 0x7ff4476045e0] Error occurred parsing angle expression 'A*sin(2*PI/T*t)'
  
  [Parsed_rotate_3 @ 0x7ff4476045e0] Failed to configure output pad on Parsed_rotate_3
  
  Error reinitializing filters!
  
  Failed to inject frame into filter network: Invalid argument
  
  Error while processing the decoded data for stream #1:0

  If I remove ’A’, ’T’, ’sin’, etc, rotate does actually work, but far from the desired behavior.

  Am I missing something to expose those params ?

• FFMPEG : Position images in video when creating slide show

  29 décembre 2015, par Jimmy

  I’m using FFMPEG shell utility in an Android app to convert users pictures to video, here’s an example command :

  cat *.jpg | ffmpeg -f image2pipe -r 10  -vcodec mjpeg -i - -vcodec libx264 -s 1280x720 -preset ultrafast slideshow.mp4 

  I used to crop images when the user import it in the app but now I would like to allow the user to reposition the image later, here’s an example :

  

  So the user could drag or zoom the image to position it in the clear area (video ratio).

  So using the ffmpeg shell command can I specify the image coordinate for each image and position the image in the video.