title: generate video containing scrolling image
body: <p>I want to generate a video [let's say 800x600] from a 800x10000 still image.</p>
  
  <p>The image has to scroll, from top to bottom as if someone was actually scrolling a page.</p>
  
  <p>If it could scroll faster over some portions and slower over others, that would be great, if not I think I could just make a few separate videos and then just stitch them up.</p>
  
  <p>I cannot find any documentation on this subject; could anyone give me a hint? Thanks for your time!</p>