src/websites/youtube.rb

   1 #
   2 # Copyright Michael Orlitzky
   3 #
   4 # http://michael.orlitzky.com/
   5 #
   6 # This program is free software: you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation, either version 3 of the License, or
   9 # (at your option) any later version.
  10 #
  11 # This program is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14 # GNU General Public License for more details.
  15 #
  16 # http://www.fsf.org/licensing/licenses/gpl.html
  17 #
  18
  19 require 'src/website'
  20 require 'cgi'
  21
  22 class Youtube < Website
  23
  24   VALID_YOUTUBE_URL_REGEX = /^(http:\/\/)?([a-z0-9]+\.)?youtube\.com\/((watch\?v=)|(v\/)|([a-z]+\#[a-z]\/[a-z]\/[0-9]\/))[a-z0-9_\-]+(\&.*)?\#?$/i
  25
  26   def self.owns_url?(url)
  27     return url =~ VALID_YOUTUBE_URL_REGEX
  28   end
  29
  30
  31   def initialize(url)
  32     super
  33
  34     # The @format variable just caches the format of the video we're
  35     # downloading. Storing it will prevent us from having to calculate
  36     # it twice.
  37     @format = 0
  38   end
  39
  40
  41   def get_video_url()
  42     video_id = self.parse_video_id()
  43
  44     # The video's URL (the "page data" URL) may be different from the
  45     # URL that was passed to the program. We support the /v/video_id
  46     # URL format, but that is *not* the main video page where we can
  47     # retrieve the "t" parameter. We can only get that from the
  48     # /watch?v=video_id form.
  49     page_data_url = "http://www.youtube.com/watch?v=#{video_id}"
  50     page_data = self.get_page_data(page_data_url)
  51
  52     # Magic.
  53     t_parameter = self.parse_t_parameter(page_data)
  54
  55     video_url = "http://www.youtube.com/get_video?video_id=#{video_id}&t=#{t_parameter}"
  56
  57     # Figure out which formats are available, and if any are,
  58     # choose the best one.
  59     available_formats = get_available_formats(page_data)
  60     desired_format = get_desired_format(available_formats)
  61
  62     if not desired_format.nil?
  63       # First we cache the format so that when we're asked for the
  64       # video filename later, we don't have to recompute the format.
  65       @format = desired_format
  66
  67       # And then stick the format parameter on the end of the URL.
  68       video_url = video_url + "&fmt=#{desired_format}"
  69     end
  70
  71     return video_url
  72   end
  73
  74
  75   def get_video_filename()
  76     # The format -> extension mapping is available on Wikipedia:
  77     #
  78     #   http://en.wikipedia.org/wiki/YouTube#Quality_and_codecs
  79     #
  80     # The default extension is .flv.
  81     extension = '.flv'
  82
  83     if [18, 22, 35, 37].include?(@format)
  84       extension = '.mp4'
  85     elsif (@format == 17)
  86       extension = '.3gp'
  87     end
  88
  89     return (self.parse_video_id() + extension)
  90   end
  91
  92
  93   protected;
  94
  95   # Get the video id from the URL. Should be relatively easy,
  96   # unless Youtube supports some URL formats of which I'm unaware.
  97   def parse_video_id()
  98     # Return nil if we get no matches below.
  99     video_id = nil
 100
 101     # Both URLs are fairly easy to parse if you handle
 102     # them one at a time. The only tricky situation is when
 103     # parameters like "&hl=en" are tacked on to the end.
 104     # We'll call /watch?v=video_id the "first form."
 105     first_form_video_id_regex = /v=([0-9a-z_\-]+)/i
 106     first_form_matches = first_form_video_id_regex.match(@url)
 107     return first_form_matches[1] if not (first_form_matches.nil? ||
 108                                          first_form_matches.length < 2)
 109
 110     # First form didn't work? Try the second.
 111     second_form_video_id_regex = /\/v\/([0-9a-z_\-]+)/i
 112     second_form_matches = second_form_video_id_regex.match(@url)
 113     video_id = second_form_matches[1] if not (second_form_matches.nil? ||
 114                                               second_form_matches.length < 2)
 115
 116     return video_id
 117   end
 118
 119
 120   # Parse out the "t" parameter from the video's page. I'm not sure
 121   # what "t" stands for, but it's located in some JSON, and is required
 122   # for the final video URL to work.
 123   def parse_t_parameter(page_data)
 124     t_parameter = nil
 125
 126     t_parameter_regex = /\"t\"\:[[:space:]]\"([^\"]+?)\"/
 127     matches = t_parameter_regex.match(page_data)
 128     t_parameter = matches[1] if not (matches.nil? || matches.length < 2)
 129
 130     return t_parameter
 131   end
 132
 133
 134   def get_available_formats(page_data)
 135     # Parse the list of available formats from the "fmt_list" Flash
 136     # variable.
 137     available_formats = []
 138     fmt_list_regex = /\"fmt_list\"\:[[:space:]]\"([^\"]+?)\"/
 139     matches = fmt_list_regex.match(page_data)
 140
 141     if matches.nil?
 142       return nil
 143     else
 144       fmts_string = CGI::unescape(matches[1])
 145
 146       fmts_string.split(',').each do |fmt|
 147         # Each "fmt" will look something like,
 148         #
 149         #   35/640000/9/0/115
 150         #
 151         # with the format identifier coming before the first slash.
 152         first_slash_idx = fmt.index('/')
 153         available_formats << fmt[0...first_slash_idx].to_i
 154       end
 155
 156     end
 157
 158     return available_formats
 159   end
 160
 161
 162   def get_desired_format(available_formats)
 163     # Check for the presence of formats, in order of preference
 164     # (quality). That is, we check for the best formats first. As soon
 165     # as a format is found to be available, we return it as the
 166     # desired format, since the first format we find is going to be
 167     # the best available format.
 168     return 37 if available_formats.include?(37)
 169     return 22 if available_formats.include?(22)
 170     return 35 if available_formats.include?(35)
 171     return 18 if available_formats.include?(18)
 172     return 34 if available_formats.include?(34)
 173     return 17 if available_formats.include?(17)
 174   end
 175
 176 end