title: ffmpeg scale down video dynamically (squeeze-back) or zoompan out to smaller than original
body: <p>I have 2 videos, I'm trying to overlay one on top of the other, and have it shrink down in an animated fashion until it appears like a picture-in-picture setup. Then, after a few seconds it should scale back up.</p>
  <p>This is what I am trying to achieve (these would be <strong>videos</strong>, <strong>not images</strong>):
  <a href="https://i.stack.imgur.com/8mXE6.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8mXE6.gif" alt="enter image description here" /></a></p>
  <p>This is the closest I've been able to get, but, crucially, zoompanning &quot;out&quot; (as opposed to &quot;in&quot;) does not appear to work; so, of course, this <strong>does not work</strong>:</p>
  <p><code>ffmpeg -i bg.mov -i top.mov -filter_complex &quot;[0:v]zoompan=z='pzoom-0.1':d=1, setpts=PTS-STARTPTS[top]; [1:v]setpts=PTS-STARTPTS+2/TB, scale=1920x1080, format=yuva420p,colorchannelmixer=aa=1.0[bottom]; [top][bottom]overlay=shortest=0&quot; -vcodec libx264 out.mp4</code></p>
  <p>Is this achievable with ffmpeg?</p>