Images and Media: img, picture, srcset/sizes, video, audio, track and iframe
Give every img a width and height, choose alt by the image's job on the page, pair srcset with sizes when the image size changes with the screen, and never put loading="lazy" on an image on the first screen. In this post we measure these rules in Chromium and WebKit: a 0.14 layout shift from an image without dimensions, sizes="auto", AVIF/WebP/JPEG XL order in picture, the half-second delay of a lazy LCP image, subtitles with track and the iframe title.
14 Nov 2026
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17 min
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6
