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I would like to animate the video by changing the object-fit property from contain to cover. However, the animation is not smooth and there is a noticeable jump. My desired outcome is to have the image container positioned at the bottom of the viewport, then smoothly translate it to the center of the viewport. Once it is centered, I want to scale the container to fit the entire window and then scale it back to its original size of 1. During this scaling process, I also want to adjust the container size to be 100% in terms of both height and width, and set the image object-fit property to cover.

I was asked yesterday about animating to/from backgroundSize: "cover" or "contain" with GSAP, so I figured I'd share the solution here in case it helps anyone else. The problem: GSAP interpolates between numbers, but how is it supposed to interpolate between something like "300px 250px" and "contain" (not a number)? So I whipped together a function that basically translates "contain" or "cover" into their px-based equivalents for that particular element at whatever size it is then. Once we've got it converted, it's easy to animate. //this function converts the backgroundSize of an element from "cover" or "contain" or "auto" into px-based dimensions. To set it immediately, pass true as the 2nd parameter. function getBGSize(element, setInPx) { var e = (typeof(element) === "string") ? document.querySelector(element) : element, cs = window.getComputedStyle(e), imageUrl = cs.backgroundImage, size = cs.backgroundSize, image, w, h, iw, ih, ew, eh, ratio; if (imageUrl && !/\d/g.test(size)) { image = new Image(); image.setAttribute("src", imageUrl.replace(/(^url\("|^url\('|^url\(|"\)$|'\)$|\)$)/gi, "")); //remove any url() wrapper. Note: some browsers include quotes, some don't. iw = image.naturalWidth; ih = image.naturalHeight; ratio = iw / ih; ew = e.offsetWidth; eh = e.offsetHeight; if (!iw || !ih) { console.log("getBGSize() failed; image hasn't loaded yet."); } if (size === "cover" || size === "contain") { if ((size === "cover") === (iw / ew > ih / eh)) { h = eh; w = eh * ratio; } else { w = ew; h = ew / ratio; } } else { //"auto" w = iw; h = ih; } size = Math.ceil(w) + "px " + Math.ceil(h) + "px"; if (setInPx) { e.style.backgroundSize = size; } } return size; } The only catch is that the image must be already loaded, otherwise it's impossible to figure out the native dimensions of the image (aspect ratio). While it's technically possible to add this functionality into CSSPlugin, it didn't seem advisable because it eats up a fair amount of kb and it's EXTREMELY uncommon for folks to want to animate to/from a background-size of cover or contain. So maybe 0.0001% of the audience would benefit but 100% would pay the kb price. Didn't seem worthwhile, so a helper function like this struck me as more appropriate. Feel free to chime in if you disagree. Happy tweening!