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• Trying to crop an image in ffmpeg using alphamerge but produces wrong alpha

  12 septembre 2021, par Alex Styl

  I am using alphamerge in order to crop an image within a circle.

  


  What I have so far is :

  


  ffmpeg -f lavfi -i "color=c=white:size=240x240" -i avatar.png -i mask.png -filter_complex \
 "[1][2]alphamerge[img]; \
 [0][img]overlay[out]" -c:v png -map "[out]" -pix_fmt rgba -t 5 -y out.mp4 2>&1


  


  with avatar.png and mask.png respectively being :

  


  

  


  This produces the following output (1 frame of the output video) :

  


  

  


  which is unexpected, given the original input is much darker than this.

  


  How can I crop the 'avatar.png' using the 'mask.png' so that the output is the avatar.png cropped in a circle and keeping the same alpha ?

  


  PS : The important bit here is for me to be able to crop the original image and maintaining the correct colors/apha of the original image. If there is an other way of doing this (other than alphamerge) I am happy to hear it.

  


• Ffmpeg Multiple Crop

  6 décembre 2019, par megaimd mega

  How can I make crop in and out from 3 to 3 seconds to a video.
  for Exemple :

  The First 3 sec Of the video to be original,

  The next 3 sec of the video to be CROP crop=iw-684:ih-516,scale=1280:720

  The next 3 sec Of the video to be original,

  The next 3 sec of the video to be CROP crop=iw-684:ih-516,scale=1280:720

  so on, until the end of the video
  Please Help Me

• How to automatically remove black bars using ffmpeg and powershell ?

  7 avril 2020, par timlwsk

  Thanks to the help of the user mklement0 I got this script to automatically convert all files in the folder "video_old" and move them into "video_new", all while keeping the original filename. Original Post.

  



  Now I want to remove the black bars in the container. I know that there is "cropdetect" but AFAIK you have to manually parse the the value into the script manually. How can I automate this process using PowerShell ?

  



  Get-ChildItem .\video_old -Filter *.mkv | ForEach-Object {
  .\ffmpeg.exe -i $_.FullName -c:v libx265 -crf 18 ".\video_new\$($_.Name)"
}