title: How to do this feature? (What's the name of this feature?)
body: <p>When I built <code>x265</code> today, I found a fancy feature as the following picture.</p>
  
  <p><img src="https://i.stack.imgur.com/BTKZa.png" alt=""></p>
  
  <p>Here comes the question, what can the feature be named? And how can we realize this feature?</p>
  
  <p>ps. Forgive me for the helpless title and tags. It's a great favor if someone can help me to tag this question correctly. </p>