Engineering · 1 min read
Ad Serving Flips the Format Priority
In general image work the goal is best compression; in ad serving the priority flips to render-everywhere, load-fast, fit-the-spec — compression ranks below compatibility.
In general image work the goal is best compression. In ad serving the priority flips: first make it render everywhere, load fast, and fit the spec, with compression ranking below that.
- Compatibility beats compression. Creatives run inside third-party webviews, in-app SDKs (MRAID), and old browsers where AVIF or WebP may not decode. JPEG, PNG, and GIF stay the safe baseline, with WebP and AVIF as a progressive upgrade plus a fallback.
- Respect the weight budget. Exchanges and DSPs cap creative size (the IAB display guideline is around 150 KB initial load). A lighter file renders before the user scrolls past, which means higher viewability and fewer dropped impressions.
- Scale multiplies pennies. A few KB saved per file times billions of impressions is real CDN and bandwidth cost plus latency, which makes an automated “compress to a size limit” pass worth running.
- Match the placement: a static banner takes JPEG or PNG, an animated placement takes GIF or WebP, and a native ad composited over varied backgrounds takes PNG or WebP with alpha.
In serving, “can it render” gets asked before “how small is it.”
References:
Related: Pair this with lossy vs lossless drives file size and the image format cheat sheet — or go back to the crop, resize, fill overview.