case-based syntax for makes_derivatives_of

option_A.rb

      makes_derivatives_of :content, when: :mime_type, is_one_of: 'application/pdf',
            derivatives: { :thumb => "100x100>" }

      makes_derivatives_of :content, when: :mime_type, is_one_of: 'audio/wav',
            derivatives: { :mp3 => {format: 'mp3'}, :ogg => {format: 'ogg'} }, processors: :audio

      # -g 30 enforces keyframe generation every second (30fps)
      # -b:v is the video bitrate
      # -acodec is the audio codec
      size_attributes = "-s 320x240"
      audio_attributes = "-ac 2 -ab 96k -ar 44100"
      makes_derivatives_of :content, when: :mime_type, is: 'video/avi',
            derivatives: { :mp4 => {format: 'mp4'}, :webm => {format: 'webm'} }, processors: :video

      makes_derivatives_of :content, when: :mime_type, is_one_of: ['image/png', 'image/jpg'],
             derivatives: { :medium => "300x300>", :thumb => "100x100>" }

option_B.rb

      makes_derivatives_of :content do |ds| 
        size_attributes = "-s 320x240"
        audio_attributes = "-ac 2 -ab 96k -ar 44100"
        case ds.mime_type
        when 'application/pdf'
          transform_datastream ds, { :thumb => "100x100>" }
        when 'audio/wav'
          transform_datastream ds, { :mp3 => {format: 'mp3'}, :ogg => {format: 'ogg'} }, processors: :audio
        when 'video/avi'
          transform_datastream ds, { :mp4 => {format: 'mp4'}, :webm => {format: 'webm'} }, processors: :video
        when 'image/png', 'image/jpg'
          transform_datastream ds, { :medium => "300x300>", :thumb => "100x100>" }
        end
      end

option_C.rb

    makes_derivatives do |obj| 
      size_attributes = "-s 320x240"
      audio_attributes = "-ac 2 -ab 96k -ar 44100"
      case obj.mime_type
      when 'application/pdf'
        obj.transform_datastream :content, { :thumb => "100x100>" }
      when 'audio/wav'
        obj.transform_datastream :content, { :mp3 => {format: 'mp3'}, :ogg => {format: 'ogg'} }, processor: :audio
      when 'video/avi'
        obj.transform_datastream :content, { :mp4 => {format: 'mp4'}, :webm => {format: 'webm'} }, processor: :video
      when 'image/png', 'image/jpg'
        obj.transform_datastream :content, { :medium => "300x300>", :thumb => "100x100>" }
      end
    end

option_D.rb

    make_derivatives_of :content, :using => :derivatives_from_content_ds

    def derivatives_from_content_ds
      size_attributes = "-s 320x240"
      audio_attributes = "-ac 2 -ab 96k -ar 44100"
      case obj.mime_type
      when 'application/pdf'
        obj.transform_datastream :content, { :thumb => "100x100>" }
      when 'audio/wav'
        obj.transform_datastream :content, { :mp3 => {format: 'mp3'}, :ogg => {format: 'ogg'} }, processor: :audio
      when 'video/avi'
        obj.transform_datastream :content, { :mp4 => {format: 'mp4'}, :webm => {format: 'webm'} }, processor: :video
      when 'image/png', 'image/jpg'
        obj.transform_datastream :content, { :medium => "300x300>", :thumb => "100x100>" }
      end
    end

option_E.rb

    makes_derivatives :generate_content_derivatives

    def generate_content_derivatives
      size_attributes = "-s 320x240"
      audio_attributes = "-ac 2 -ab 96k -ar 44100"
      case obj.mime_type
      when 'application/pdf'
        obj.transform_datastream :content, { :thumb => "100x100>" }
      when 'audio/wav'
        obj.transform_datastream :content, { :mp3 => {format: 'mp3'}, :ogg => {format: 'ogg'} }, processor: :audio
      when 'video/avi'
        obj.transform_datastream :content, { :mp4 => {format: 'mp4'}, :webm => {format: 'webm'} }, processor: :video
      when 'image/png', 'image/jpg'
        obj.transform_datastream :content, { :medium => "300x300>", :thumb => "100x100>" }
      end
    end