title: how to batch combine two sequence of images with an alpha channel using ffmpeg or imagemagick?
body: <p>Other tools or Simple APIs are also welcome.</p>
  
  <p>I have a sequence of pngs with alpha that I want to overlay on top of a few videos.
  Using ffmpeg would be fantastic, but using imagemagick is also acceptable. I could extract all the frames in the video and use imagemagick to batch blend every frame then re-encode (re-encoding is acceptable).</p>