require 'rubygems'
require 'activesupport'
require 'digest/md5'

class Signature
  PASSWORD    = 'YOUR_SECRET_PASSWORD_HERE'   # use this password for nginx directive "secure_link_md5"
  DIR         = 'flv'                         # the internal nginx location to access to media files
  SERVER_NAME = 'http://your_server.com:8080' # nginx listen address and port
  attr_reader :expiration_time, :file_name, :md5

  def initialize(file_name)
    @expiration_time = (Time.now + 2.hours).to_i
    @file_name       = file_name
    md5_calculate
  end

  def generate
    # nginx secured URL to access to media files, "video" is the location, not real directory on filesystem
    "#{SERVER_NAME}/video/#{@md5}/#{expiration_time}/#{file_name}"
  end


  private

  def md5_calculate
    s    = "#{PASSWORD}#{@expiration_time}/#{DIR}/#{@file_name}"
    a    = Base64.encode64(Digest::MD5.digest(s))
    @md5 = a.tr("+/", "-_").sub('==', '').chomp
  end
end


url = Signature.new('video1.flv')
puts url.expiration_time #=> 1326559618
puts url.md5             #=> HLz1px_YzSNcbcaskzA6nQ
puts url.generate        #=> http://your_server.com:8080/video/HLz1px_YzSNcbcaskzA6nQ/1326559618/video1.flv