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• FFmpeg - center crop image overlay

  21 juillet 2020, par ClassA

  Here is the information about my input files, player and command I'm using :

  


  

  


  

  • Input Video Dimensions = 1080 x 1920

  


  • Input Image Dimensions (overlay - Red in image) = 1080 x 1794

  


  • Player dimensions (Black in image) = 1080 x 1794

  


  • Video size (scaled to fit in player - Blue in image) = 1010 x 1794

  


  


  My current command is :

  


  -ffmpeg -ss valueLeft -i inputVideo -i inputOverlay -t to -filter_complex scale=playerWidth:trunc(ow/a/2)*2,overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2 -c:v libx264 -preset ultrafast outputPath


  


  The playerWidth is the width of the video, scaled to fit in the player (blue/video in the image above).

  


  ---

  


  The problem I have is that the video is scaled inside the player to fit inside the player, this means that I might have values like 999.

  


  To counter this, I can change the width to 998 or 1000, but the overlay image will be out by one pixel. I know one pixel is not a lot, but in my use case, it has to be precisely the same as it was in the player.

  


  Besides that, the video aspect ratio will also change when doing this.

  


  My question :

  


  How can I center crop the overlay, despite the size of the video or the overlay image, to get the following result :

  


  

  


  EDIT :
It would be great if I could instead use the video's original dimensions and crop the overlay (if it is bigger than the video).

  


• ffmpeg blend multiple files

  7 octobre 2022, par Gregory

  I currently have the following command that allows me to overlay files and apply a blending mode. This works well when I overlay 2 files, however when I try to overlay a third image, then the generated output is incorrect.

  


  

  • Blue

  


  • GroundShadow (softlight)

  


  • FeetShadows (multiply)

  


  


  Command :

  


  ffmpeg \
    -i /Users/me/Downloads/blue.gif \
    -i /Users/me/Downloads/GroundShadow.gif \
    -i /Users/me/Downloads/FeetShadows.gif \
    -y \
    -filter_complex "[0:v][1:v]blend=all_mode='softlight'[v1],[v1][2:v]blend=all_mode='multiply'[v2],[v2]split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" \
    /Users/me/Downloads/preview.gif


  


  





  


  


  


  


  



  


  


  


  


  Expected (ignore that it's animated)	Result

  


  


  The background color is washed for some reason.
I'm not sure if i'm applying the blending filters in the right order or if you should split between the images to then apply the blend ? Or something else ?

  


• Why are the colors transposed in my webm thumbnails ?

  9 décembre 2022, par Peter Chaplin

  I have been using ffmpeg to generate webm files from png frames, and the webm files run ok in my video player, but the thumbnail colours appear transposed - blue replacing red, purple replacing orange, brown replacing green. I've also encountered issue uploading the webm to an image hosting site (which normally does support webms), though this might be an issue on their end.
I'm on Ubuntu 22.04.1 LTS

  


  Does anyone know what might be causing this, and how to fix it ? Or how to check whether the webm files are ok or corrupted ?

  


  *Edit : ok, here's a side-by-side comparison of the thumbnails that appear in my file explorer - mp4 on the left and webm on the right.
Both were generated from the same set of pngs, using the same command except with the filename extension changed.

  


  

  


  Specifically,

  


  ffmpeg -framerate 24 -i Panel2Humanized/frame%04d.png panel2humanskin.webm


  


  and

  


  ffmpeg -framerate 24 -i Panel2Humanized/frame%04d.png panel2humanskin.mp4


  


  Both look the same when opened with a video player. It looks like the mp4 thumbnail grabbed the 1st frame while the webm grabbed the last, but the colors should be the same in each. (The text-bubble in the top-left is yellow in the mp4).

  


  *Follow-up : Apparently my WebMs are being generated in GBRP (Green-Blue-Red Planar) pixel format, the site I was trying to upload to requires YUV420P (Luma/Chroma 4:2:0 Planar) format, maybe that's the issue ? I'm still not sure exactly what that means or how to fix it.

  


  *Final follow-up : Looks like I needed to change the argument to :

  


  ffmpeg -framerate 24 -i Panel2Humanized/frame%04d.png -pix_fmt yuv420p paned2humanskin.webm