The same is possible with vanilla lazyload, e.g. using a fade in transition. The automatic "sizes" calculation does seem like a cool feature, but I wonder there's a performance issue with this as this is the argument why vanilla lazyload library doesn't have this. The vanilla lazyload library support lazyload of both images, background images, iframe, HTML videos and lazy loading in a specific container. I guess both libraries have pros and cons. When looking at the repository it does seems it haven't changes since the spring, while the vanilla lazyload seems to have more active development.