parrot-bpm.rb

#!/usr/bin/env ruby
require "optparse"

OPTS={
  :bpm => 60.0,
  :output => "output.gif",
}
opt = OptionParser.new

opt.on("-b BPM", "--bpm=BPM") {|v|
  OPTS[:bpm] = v.to_f
}

opt.on("-o OUTPUT", "--output=OUTPUT") {|v|
  OPTS[:output] = v
}


(class<<self;self;end).module_eval do
  define_method(:usage) do |msg|
    puts opt.to_s
    puts "error: #{msg}" if msg
    exit 1
  end
end

begin
  rest = opt.parse(ARGV)
  # XXX: this forbids option-less argument
  if rest.length != 0
    usage
  end
rescue
  usage $!.to_s
end

$debug = false

def dp str
  if $debug
    p str
  end
end

system("wget -O parrot.gif https://cultofthepartyparrot.com/parrots/hd/parrot.gif")


ORIGINAL_PARROT_PER_SEC = 1/ (10 * 0.05)

bpm = OPTS[:bpm]
pps = (bpm / 60)
speed_rate = 1/ pps * ORIGINAL_PARROT_PER_SEC

dp "pps => #{pps}, rate => #{speed_rate}"
cmd = "ffmpeg -y -i parrot.gif -filter:v \"setpts=#{speed_rate}*PTS\" #{OPTS[:output]}"
dp cmd
system(cmd)