Create a slideshow with different sized images, scaling to fit not stretch, using ffmpeg and imagemagick. Runs pretty fast thanks to GNU parallel

• GNU Parallel
• ffmpeg
• imagemagick

$ sudo apt-get install ffmpeg parallel imagemagick

Usage:
./scaledSlideshow.sh path_to_images extension xres yres fps out_file
e.g.
./scaledSlideshow.sh ./images/ jpg 2560 1440 60 out.mp4 [ffmpeg args]
This will take all images in ./images/ with a .jpg extension and make a 2560x1440 60fps slideshow and place the output file in ./out.mp4

git clone 'https://github.com/DavidoRotho/ffmpeg-slideshow.git'
cd ffmpeg-slideshow/
chmod +x ./scaledSlideshow.sh
./scaledSlideshow.sh ../ jpg 2560 1440 60 ../out.webm

Run this block in a folder full of jpgs to make a 1440p 60fps slideshow out of them