title: Use single attachment for video/image in paperclip
body: <p>I am using paperclip for uploading file ( video and images).
  Have used the same attachment(source) for both video and images.</p>
  
  <pre><code>class Media &lt; ActiveRecord::Base
    belongs_to :memory
    validates_attachment_presence :source
    validates_attachment_content_type :source,
      :content_type =&gt; ['video/mp4', 'image/png', 'image/jpeg', 'image/jpg', 'image/gif']
  end
  </code></pre>
  
  <p>Now I wanted to display different error messages in different cases. </p>
  
  <ol>
  <li>When uploading file is image type but not the jpg/png/jpeg/gif.</li>
  <li>When uploaded file is video type but not the mp4 </li>
  </ol>
  
  <p>How can i achieve this ?
  Any help would highly appreciated.</p>