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What are Next-Gen Formats?

Next generation image formats are newer formats such as WebP, AVIF, and JPEG XL that seek better compression, additional features, or both. The term is informal and changes as formats and support evolve.

How Next-Gen Formats work

The phrase comes largely from Lighthouse, whose audit “Serve images in next-gen formats” is where many developers meet it. The list behind the label has changed: Lighthouse 6 described the formats as JPEG 2000, JPEG XR, and WebP, while Lighthouse 12 names WebP and AVIF. Chrome’s documentation now titles the audit “Serve images in modern formats” and says it moved into the “Improve image delivery” insight as of Lighthouse 13. JPEG XL (ISO/IEC 18181) is usually counted as well. The candidates differ substantially in lossy and lossless modes, alpha handling, animation, high dynamic range, and metadata, and adoption depends on encoders, browsers, operating systems, and editing tools, not on age alone.

Key facts

  1. In a Lighthouse report the label has a precise meaning. Lighthouse 12 judges the image responses the browser actually loaded: it examines only those typed as BMP, JPEG, or PNG and lists one when its estimated AVIF saving is at least 8,192 bytes. An image served as JPEG XL therefore drops off the list because it is not examined, not because it counts as modern, and when a browser skips a JPEG XL <source> and loads the JPEG fallback, that JPEG is examined. The saving is the loaded image’s size minus an estimated AVIF size that does not come from an AVIF encoder: the estimate is the average of half the size of a JPEG re-encode at quality 0.92 and 80 percent of a WebP re-encode at quality 0.85, both requested from the browser, and for images over 2,000 KiB, or once 5 seconds have been spent re-encoding, it is computed from pixel dimensions alone. Treat the reported savings as an indication to verify.
  2. The formats are different designs, not interchangeable wrappers. AVIF stores AV1-coded images in a HEIF file. WebP is a RIFF container holding VP8 lossy or WebP lossless data. JPEG XL has its own codestream and box-based file format and, alone among the three, can losslessly transcode an existing JPEG and restore the identical JPEG file later.
  3. Browser support has to be checked per format and per feature. Per caniuse data, WebP is fully supported in Safari from version 16.0, with versions 14.0 to 15.6 requiring macOS 11 or later; AVIF dates from Chrome 85 and Firefox 93 but only from Safari 16.4 and Edge 121 in full. MDN lists JPEG XL from Chrome 155, Edge 155, Firefox 158, and Safari 17; caniuse agrees except that it does not yet list Edge 155, and it marks Safari’s support as partial: still images only, without progressive decoding. In a <picture> element the browser skips any <source> whose type it does not support, which is what makes a JPEG or PNG fallback work.
  4. Decoding in browsers says little about the rest of a toolchain. Pillow’s documentation, for instance, says it saves only 8-bit AVIF and decodes every AVIF as 8-bit RGB or RGBA, and sharp’s documentation says AVIF image sequences are not supported. Check editors, metadata tools, and server-side libraries separately for each feature you depend on.
  5. Smaller output depends on the content. MDN cites lossy WebP as 25 to 35 percent smaller on average than JPEG at visually similar compression levels and lossless WebP as typically 26 percent smaller than PNG, but averages do not transfer to every image: libavif contributors describe lossless AVIF as efficient for photo-like images and expect it to do much worse than lossless WebP on graphical content. Compare candidates on your own photographs, graphics, and transparent images at the quality you intend to ship.

When Next-Gen Formats matter

Serve a newer format when measured size and quality gains on your own images justify the extra encoding and storage. Keep a JPEG or PNG fallback, for example through a <picture> element whose <source> entries declare their media type, because browser, decoder, editing, and metadata support can differ.

How Transloadit helps with Next-Gen Formats

Transloadit’s image formats table lists WebP, AVIF, and JPEG XL (JXL) as formats its ImageMagick-based Robots, including /image/resize, can read and write, and that Robot’s format parameter accepts any format the table marks as writable.

The table is paginated and sorted by name, so the WebP row is on a later page. The /image/resize documentation describes its quality parameter for JPG and PNG only, so compare size and quality of the output on your own images.

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