I've seen some very subtle moving backgrounds that were quite appropriate for the sites they were on. It's probably too difficult for software to tell the diff

I've seen some very subtle moving backgrounds that were quite appropriate for the sites they were on. It's probably too difficult for software to tell the difference between something like a high brow long form interactive article, a tasteful hero banner background, and an annoying popover or sidebar ad. My least favorite auto-playing videos in a site I use regularly are in the Netflix UI.