title: Option loop not found in video input using ffmpeg
body: <p>I'm trying to merge a image to a video using <code>ffmpeg</code>.</p>
  
  <p>This command works to me: <code>ffmpeg -i merged-video.mp4 -loop 1 -i resized-image.png -shortest -c:a copy out.mp4</code></p>
  
  <p>But it's not working when I do it in node.js, using <code>fluent-ffmpeg</code>.</p>
  
  <p>My code is like this bellow:</p>
  
  <pre><code>const ffmpeg = require('fluent-ffmpeg');
  
  ffmpeg()
      .addInput(mergedVideo)
      .loop(1)
      .addInput(image)
      .audioCodec('copy')
      .outputOptions([
          '-pix_fmt', 'yuv420p',
          '-shortest'
      ])
      .on('error', err =&gt; reject(err.message))
      .on('end', resolve)
      .save(finalResultVideo);
  </code></pre>
  
  <p>But it's getting error <code>ffmpeg exited with code 1: Option loop not found.</code></p>