title: How to join two images into one with FFmpeg?
body: <p>There are two images: <em>a.jpg</em> and <em>b.jpg</em>.</p>
  
  <p>I just want to know how to join them into one image using <code>ffmpeg</code>.</p>
  
  <p>How should I finish the <code>ffmpeg -i a.jpg -i b.jpg</code> command to get a <em>c.jpg</em> output image?</p>
  
  <p>This is an example of what I am trying to achieve:</p>
  
  <ol>
  <li><p><em>a.jpg</em></p>
  
  <p><img src="https://i.stack.imgur.com/qgOYV.jpg" alt="a.jpg"></p></li>
  <li><p><em>b.jpg</em></p>
  
  <p><img src="https://i.stack.imgur.com/8K4VM.jpg" alt="b.jpg"></p></li>
  <li><p><em>c.jpg</em></p>
  
  <p><img src="https://i.stack.imgur.com/WCrOL.png" alt="a.jpg and b.jpg side-by-side on one image"></p></li>
  </ol>