Little script to download and convet music

download_song.rb

#!/usr/bin/env ruby

=begin
README
======

Download any youtube video, in the original format ogg without 
loosing quality, and also convert a mp3 from the ogg.
You have to decide if the mp3 quality is enough for you. Or you
can adjust the parameters of the conversion if you need the mp3
to a better quality.

Buy each downloaded music before download it.

Feel free to fork, or make a rubygem if you want.

Dependencies
============

* ffmpeg (In osx with brew, a just "brew install ffmpeg" is enough).
* Ruby (Tested in 1.8 and 1.9.2)
* Ruby mechanize library (gem install mechanize)

Installation
============

1.- Give it execution permissions.
2.- [Optional] Put it in your path. Maybe ~/bin.

License
=======

----------------------------------------------------------------------------
"THE BEER-WARE LICENSE" (Revision 42):
<guillermo@cientifico.net> wrote this file. As long as you retain this notice
you can do whatever you want with this stuff. If we meet some day, and you 
think this stuff is worth it, you can buy me a beer in return Guillermo 
Álvarez Fernández
----------------------------------------------------------------------------

=end


require 'rubygems'
require 'mechanize'
require 'cgi'


class Video
  attr_reader :title, :url
  def initialize(agent, title, url)
    @agent, @title, @url = agent, title, url
  end

  def process!
    file = download
    extract_audio(file)
  end

  def inspect
    "#<Video:#{title}>"
  end

  protected

  def file_name
    title.gsub(/\W+/,'-')
  end
  
  def extract_audio(file)
    format = `ffmpeg -i #{file} 2>&1`[/Stream.*Audio\: (\w+)/,1]
    case format
    when "vorbis"
      $stderr.puts("Extracting to original format #{file_name}.ogg ...")
      system("ffmpeg -i #{file} -vn -acodec copy #{file_name}.ogg 2>&1")
      $stderr.puts("Converting to mp3             #{file_name}.mp3 ...")
      system("ffmpeg -i #{file} -vn -f mp3 #{file_name}.mp3 2>&1")
    when 'aac'
      $stderr.puts("Extracting to original format #{file_name}.ogg ...")
      system("ffmpeg -i #{file} -vn -acodec copy #{file_name}.aac 2>&1")
      $stderr.puts("Converting to mp3             #{file_name}.mp3 ...")
      system("ffmpeg -i #{file} -vn -f mp3 #{file_name}.mp3 2>&1")
    else
      $stderr.puts "Unsoported flv adudio format #{format}"
    end
  end  
  def download
    flv_path = file_name+".flv"
    puts "Downloading                   #{flv_path} (#{@title}) at #{url} ..."
    File.open(flv_path,'w') do |f|
      f.write @agent.get(flv_video_url).body
    end
    flv_path
  end
  
  def flv_video_url
    return @flv_path if defined?(@flv_path)
    flashvars = (video_page / "embed")[0]["flashvars"]
    path = flashvars.split("&").find{|var|
      var.split("=").first == "url_encoded_fmt_stream_map" rescue false
    }.split("=")[1]
    video_path = CGI.unescape(path).split("&").first.split("=")[1]
    @flv_path = CGI.unescape( video_path )
  end

  def video_page
    @page ||= @agent.get(@url)
  end
end

class YouTube
  def initialize
    @agent = a = Mechanize.new { |agent|
      agent.user_agent_alias = 'Mac Safari'
    }
  end
  
  def search(term)
    url = "http://www.youtube.com/results?search_query=#{CGI.escape(term)}&aq=f"
    page = @agent.get(url)
    videos = (page / "#search-results h3 a").map do |result|
      Video.new(@agent, result["title"], "http://www.youtube.com"+result["href"] )
    end
  end
end


if File.expand_path($0) == File.expand_path(__FILE__)
  
  $stderr.puts "Did you have the rights for doing this? (Yes/no)"
  exit(0) unless %w(yes sure! y ye yeah sure).include? ($stdin.gets.strip).downcase

  videos = YouTube.new.search(ARGV.join(" "))
  
  puts "Select a video to download"
  videos.each_with_index do |video,index|
    puts "\t #{index+1} - #{video.title}"
  end
  selected = $stdin.gets.strip.to_i
  
  unless videos.size < selected || selected == 0
    videos[selected].process!
  end  


end