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• Merge a sequence of JPEG images into a grid losslessly with FFmpeg

  20 janvier 2020, par Mody

  I have a sequence of images that are blocks of a larger image, which together make up the whole image. The blocks are the result of splitting the original image along evenly spaced horizontal and vertical lines, so they don’t have weird dimensions.

  Is there a way to combine them with FFmpeg (or something else like ImageMagick) without re-encoding the images ?

  This answer suggests the hstack or vstack FFmpeg filter, but my image blocks aren’t necessarily the full width or the full height of the original image.

  ---

  Like this :

  

  Perhaps this could be achieved with multiple FFmpeg commands using hstack or vstack (I’d prefer just one command though). Or with a complex filter ?

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  e.g.

  ---

  Edit : I tried using filter_complex with FFmpeg :

  ffmpeg -i 0.jpg -i 1.jpg -i 2.jpg -i 3.jpg -i 4.jpg -i 5.jpg \
  
  -filter_complex "[0][1]hstack=inputs=2[row 0]; \
  
                   [2][3]hstack=inputs=2[row 1]; 
  
                   [4][5]hstack=inputs=2[row 2]; 
  
                   [row 0][row 1][row 2]vstack=inputs=3[out]" \
  
  -map "[out]" -c copy out.jpg

  but it can’t filter and copy streams at the same time.

• FFMpeg : scale down videos with maximum width and height while maintaining aspect ratio

  20 février 2021, par R3D34THR4Y

  In my program the user can input any video file he wants and have it transcoded ready for social media no matter its dimensions and aspect ratio.
The "export profiles" have many variables but the important ones here are maxheight and maxwidth.

  


  The FFMpeg filters must output a video that follows the following rules :

  


  

  • If the video is vertical, permutate the maxheight and maxwidth values (social media considers both 1280x720 and 720x1280 as "720P")

  


  • The video must not have a height superior to maxheight or a width superior to maxwidth.

  


  • The original video and exported video have the same aspect ratio and no distortion occurs.

  


  • No padding or cropping should occur.

  


  • The video should not be scaled if it is already under those maximum dimensions (no upscaling).

  


  • The function must work even with odd input resolutions.

  


  


  I have tried finding a combination of filters that do that but I haven't been able so far, either the video gets distorted or it gets huge black bars if the aspect ratio isn't right, the solution may be simple but I'm a beginner on this library so I'm probably just missing an easy solution.

  


  My current solution :

  


  ffmpeg -i input.mp4 -vf [in] scale=1280:720:flags=lanczos:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2,setsar=1 [res]; [res] format=yuv420p [format] -c:v libx264 -c:a aac -movflags +faststart output.mp4


  


  Thanks for reading

  


• Anomalie #4272 : Vignettes considérée comme orphelins lors de la suppression des documents inutilisés

  11 février 2019, par Fabrice Véronneau

  Discussions sur le forum à ce sujet
  https://forum.spip.net/fr_271022.html
  https://forum.spip.net/fr_270796.html?debut_forums=%40270837#forum270837