title: FFmpeg — calculate zoompan filter duration
body: <p>I want to make 30 seconds video with smooth small zooming effect of an image. What i do:</p>
  
  <p><code>ffmpeg -y -loop 1 -i 1.png -vf "zoompan=z='min(max(zoom,pzoom)+0.0015,1.1)':d=1:x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':s='1000x1000'" -c:v libx264 -t 30 1.mp4</code></p>
  
  <p>How to modify my ffmpeg zoompan params for zoom effect during 30 seconds (all video time)? Now it produce 3 seconds effect at all. Docs says:</p>
  
  <p><code>d — Set the duration expression in number of frames. This sets for how many number of frames effect will last for single input image.</code></p>
  
  <p>But my experiments with <code>d</code> falied. Thanks!</p>