mashup.rb

#!/usr/bin/env ruby
require 'rubygems'
require 'pit'
require 'scissor/echonest'

config = Pit.get('echonest.com', :require => {
    'api_key' => 'your Echo Nest API key'
  })

Scissor.echonest_api_key = config['api_key']
Scissor.logger.level = Logger::DEBUG

def main
  if ARGV.size != 3
    puts "usage: #$0 masterfile slavefile outfile"
    exit
  end

  masterfile, slavefile, outfile = ARGV

  master = Scissor(masterfile).beats
  slave = Scissor(slavefile).beats

  results = []
  master.each_with_index do |chunk, index|
    if slave[index]
      pitch = slave[index].duration / chunk.duration * 100
      results << slave[index].pitch(pitch)
    else
      break
    end
  end

  Scissor.mix([Scissor.join(master), Scissor.join(results)], outfile, { :overwrite => true })
end

main