The way you'll handle conditional styling is to use a lambda
to determine what type of content you're dealing with. We've done this before with an earlier version of Rails / Paperclip:
#app/models/attachment.rb
Class Attachment < ActiveRecord::Base
has_attached_file :file,
styles: lambda { |a| a.instance.is_image? ? {:small => "x200>", :medium => "x300>", :large => "x400>"} : {}}
validates_attachment_content_type :file, :content_type => [/\Aimage\/.*\Z/, /\Avideo\/.*\Z/]
private
def is_image?
attachment.instance.attachment_content_type =~ %r(image)
end
end