AVIF: 78KB -> 31KB but +90ms decode on low-end

AVIF: 78KB -> 31KB but +90ms decode on low-end
AVIF beats WebP on file size but the decode cost isn't zero on weak CPUs.
— Hero image: JPEG 210KB -> WebP 78KB -> AVIF 31KB
— On a high-end phone decode was 8ms; on a 2019 mid-tier Android it was 95ms — pushing render delay
— For the LCP image specifically, WebP was faster end-to-end on p75 hardware despite +47KB
— AVIF won everywhere below-the-fold where decode timing doesn't gate LCP
Byte count isn't the finish line; decode-to-paint is.
Takeaway: WebP for the LCP image at p75, AVIF for the rest.