title: Reencode videos from 30fps to 60fps using ffmpeg
body: <p>If I have an mp4 with 30 fps, how do I re-encode it to 60 fps using ffmpg <strong>without</strong> making the movie speeding up faster (still looking normal)?</p>
  
  <p>My ffmpeg</p>
  
  <pre><code>ffmpeg version 3.4.6-0ubuntu0.18.04.1 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)
  </code></pre>