title: how to fade two images with ffmpeg
body: <p>I have two images and I want to create a simple fading transition between them. </p>
  
  <p>I also want the final output to be a sequence of images rather than a video? 
  So if the fading transition was 10 frames long I'd want the output to be a sequence of 10 images.</p>
  
  <p>How can I achieve this with ffmpeg?</p>