Script to encode with HandbrakeCLI (x264) 720p, high image quality, low file size

gistfile1.rb

#!/usr/bin/env ruby 
# encoding: utf-8

# x264 presets guide : https://forum.handbrake.fr/viewtopic.php?f=6&t=19426
X264    = "b-adapt=2:rc-lookahead=50:me=umh:bframes=5:ref=6:direct=auto:trellis=2:subq=10:psy-rd=1.0,0.10:analyse=all"
FORMAT  = "--optimize --format mp4"
QUALITY = "--ab 64 --mixdown mono --quality 23 -e x264 -x '#{X264}'"
SIZE    = "--width 1280 --height 720"

ARGV.each do |param|
  Dir.glob(param) do |entry|
    next unless File.file?(entry)
    
    # Open the source file
    # Needed to get its mtime
    source_file = File.new(entry)
    
    # Use a sanitized filename with -720p extension
    destination = source_file.path.gsub(/(.*)[.][a-zA-Z0-9]+$/, "\\1-720p.mp4")

    # Compress video file
    # -v0 flag disabled most of the verbosity
    system "/Applications/HandBrakeCLI -v0 -i '#{source_file.path}' -o '#{destination}' #{FORMAT} #{QUALITY} #{SIZE}}"

    # Set original file's modification time + current time for access time
    File.utime(Time.now, source_file.mtime, destination)
  end
end

-mixdown mono wut?

How do I use this script?