title: Stack gifs with FFmpeg without loss of quality
body: <p>I have two animated gifs of the same duration and size that I am trying to stack vertically with ffmpeg: </p>
  
  <pre><code>ffmpeg input_1.gif -i input_2.gif -filter_complex vstack -q:v 1 output.gif
  </code></pre>
  
  <p>The problem is that resulting gif experience quite some loss of quality. Furthermore, it seems that option <code>-q:v</code> has no effect at all, regardless of supplied value and (valid) positioning within command. </p>
  
  <p>Does anybody know a way to overcome it? </p>