play an audio file at a particular speed

rit.rb

#!/usr/bin/env ruby

# rit.rb - play an audio file at a particular speed
#
# usage: ruby rit.rb <speed> <path_to_audio_file>
#
# <speed> is a float which acts as a multiplier. 1.0 is normal speed, 2.0
# is double speed, 0.5 is half speed, and so on.
#
# put 0 for <speed> for a fun easter egg.
#
# dependencies are mplayer and the open4 gem.

require "open4"

if ARGV.length != 2
  puts "Usage: #$0 <speed> <path_to_audio_file>"
  exit
end

speed, path = *ARGV
speed = speed.to_f

raise "file '#{path}' doesn't exist" unless File.exists? path

cmd = ["mplayer", "-slave", "-quiet", path]
pid, stdin, stdout, stderr = Open4.popen4(*cmd)

begin
  line = stdout.gets
  raise "file '#{path}' isn't a valid audio file" if line.nil?
end until line.chomp == "Starting playback..."

Thread.new { Process.wait(pid); exit }

if speed == 0.0
  speed = 1.0
  loop do
    stdin.puts "speed_set #{speed}"
    speed += (rand(3) - 1) / 100.0
    sleep 0.5
  end
else
  stdin.puts "speed_set #{speed}"
  loop { sleep 0.5 }
end