Very brittle, but maybe useful

makevideo.rb

# for when you have a bunch of images in a dir that are not *quite*
# numbered the way ffmpeg wants them to be, e.g.
# image-1, image-2, ... image-10, image-11, ... image-100, image-101

if ARGV.length < 1
  puts "Usage: ruby makevideo.rb name-of-directory-with-all-your-dang-images-in-it"
  exit
end

dir = ARGV[0]

unless File.directory?(dir)
  puts "#{dir} isn't a directory :("
  exit
end

# assumes png -- you can change it, but be sure to change it everywhere

filenames = Dir["#{dir}/*.png"]

out_dir = "#{dir}-renumbered"
`mkdir #{out_dir}`

num_digits = 3 # increase this if you have > 999 images...!

print "Renumbering #{filenames.length} files: "

filenames.each do |filename|
  # this expects <something>-2.png, <something>-2.png, etc.
  # if there aren't hyphens preceding your numbers, e.g.
  # pic1.png, pic2.png, pic3.png
  # you could substitute a regex like
  # /pic(\d+)\.png/
  num = filename.match(/-(\d+)\.png/)[1].rjust(num_digits, "0")
  print "#{num}... "
  `cp #{filename} #{out_dir}/renumbered-#{num}.png`
end

puts ""

out_video = "output-#{dir}.mp4"

puts "Making video"
`cd #{out_dir}; ffmpeg -y -r 24 -i "renumbered-%0#{num_digits}d.png" -c:v libx264 -crf 18 -preset slow -pix_fmt yuv420p #{out_video}`

puts "Okay! Your video is in #{out_dir}"