What 'next-gen' means here
Lighthouse means WebP or AVIF (sometimes JPEG XL in experiments). WebP is the one you can produce locally on any machine, including Safari with this converter's WASM encoder.
Why it matters
- The audit names files. That is your to-do list.
- CMS themes often hardcode .jpg extensions.
- CDNs can transcode, but a real .webp file is simpler to reason about.
How to do it
- Download each flagged file.
- Bulk convert. Keep meaningful filenames, change extension to .webp.
- Update HTML/CMS. Redirect old URLs if they are indexed.
Settings that work
Match visual quality to the original. 80% is the default starting point.