title: Filter a list based on a multiple options
body: <p>I want to return a list of files from a folder, based on a specific file extension.</p>
  
  <p>At the moment, I get all files. How do I filter out certain types?</p>
  
  <p>At the moment, my code looks like this:</p>
  
  <pre><code>public static List&lt;FileInfo&gt; BuildListOfFiles()
  {
      var d = new DirectoryInfo(Constants.FolderToMonitor);
      if (d.Exists)
      {
          var files = (from file in d.EnumerateFiles() select file).ToList();
          return files;
      }
      return null;
  
  }
  </code></pre>
  
  <p>But I only want </p>
  
  <blockquote>
    <p>*.mp4, *.mpg, *.avi, *.mpeg</p>
  </blockquote>
  
  <p>I think I need another .Where, but not sure how to handle multiple types cleanly.</p>