You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: audioboom_onebox.rb
    path of file: ./repos/discourse/lib/onebox/engine
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module Onebox
  module Engine
    class AudioboomOnebox
      include Engine
      include StandardEmbed

      matches_regexp(%r{^https?://audioboom\.com/posts/\d+})
      always_
    
      def placeholder_html
        oembed = get_oembed

        <<-HTML
          <img
            src="#{oembed.thumbnail_url}"
            style="max-width: #{oembed.width}px; max-height: #{oembed.height}px;"
            #{oembed.title_attr}
          >
        HTML
      end