#!/usr/bin/env ruby
# - encoding: utf-8 -
#
# Intro (in German):
# https://depone.net/2016/03/01/video-in-animiertes-gif-konvertieren/
#
# Hat tip for the palette trick to:
# http://blog.pkh.me/p/21-high-quality-gif-with-ffmpeg.html

require 'tmpdir'

DEFAULT_WIDTH=400
DEFAULT_FPS=10
name = ARGV[0]

if ARGV.length == 0 or name == '--help'
  puts <<EOL
usage: convert-to-gif <filename> [<width>] [<fps>]

Supply a video file that should be converted as <filename> and resize
the resulting GIF to <width> with <fps> frames per second. Width and
frames per second are optional parameters.

$ convert-to-gif video.mp4

Will result in a GIF with #{DEFAULT_FPS} fps that is #{DEFAULT_WIDTH}
pixel wide.
EOL
  exit
end


Dir.mktmpdir do |tmpdir|
  palette = File.join(tmpdir, "palette.png")

  unless File.exist?(name)
    abort "File [#{name}] does not exist. Please see --help."
  end

  width = ARGV[1] || DEFAULT_WIDTH
  fps = ARGV[2] || DEFAULT_FPS

  basename = File.basename(name, ".*")
  filters="fps=#{fps},scale=#{width}:-1:flags=lanczos"

  system("ffmpeg -i #{name} -vf '#{filters},palettegen' -y #{palette}")
  system("ffmpeg -i #{name} -i #{palette} -lavfi '#{filters} [x]; [x][1:v] paletteuse' -y #{basename}.gif")
end