PERFORMANCE · SEO GLOSSARY
AVIF (SEO)
The AVIF (AV1 Image File Format) image format — offering even better compression than WebP (typically 20–50% smaller at equivalent quality) — which improves LCP and page performance but has less complete browser support than WebP, typically requiring a fallback strategy using the `<picture>` element.
Definition
AVIF (AV1 Image File Format) is a modern image format based on the AV1 video codec compression technology. It offers compression efficiency superior to both JPEG and WebP — producing smaller files at equivalent visual quality, particularly for photographic content and images with gradients. AVIF vs WebP: AVIF produces 20–50% smaller files than WebP at equivalent quality; WebP produces 25–35% smaller files than JPEG. AVIF is therefore the best available format for image quality-to-size efficiency. Browser support (as of 2026): Chrome, Firefox, and Edge support AVIF; Safari has added AVIF support in more recent versions. Support is widespread enough that AVIF is worth serving to supported browsers with a WebP fallback for others and a JPEG/PNG final fallback for any remaining unsupported environments. Implementation using `<picture>`: `<picture><source srcset="image.avif" type="image/avif"><source srcset="image.webp" type="image/webp"><img src="image.jpg" alt="..."></picture>`. The browser uses the first `<source>` it supports. CDN and CMS support: major CDN providers (Cloudflare, Fastly, Cloudinary, imgix) support AVIF conversion and serving based on Accept header content negotiation. CMS plugins (Imagify, ShortPixel) also offer AVIF conversion. For e-commerce sites with large product image catalogues, CDN-level automatic AVIF conversion is the most efficient implementation path. AVIF for LCP: the LCP image is the highest-priority candidate for AVIF optimisation — the format that achieves the smallest file size for the most performance-critical image on the page.
Why it matters for SEO
AVIF represents the next step beyond WebP in image efficiency. For sites where LCP is image-determined (the majority of commercial websites), moving from WebP to AVIF for the LCP image can produce measurable CrUX LCP improvements. The browser support landscape in 2026 makes AVIF viable with WebP fallback — it is no longer an experimental format. For performance-sensitive sites where every millisecond of LCP matters for conversion rates and rankings, AVIF is the current state of the art.
How DeepSEOAnalysis checks this
DeepSEOAnalysis checks whether the LCP image on audited pages is served in AVIF format (with appropriate fallbacks). Images served as JPEG or WebP are noted as candidates for AVIF optimisation. CrUX LCP data reflects the real-world performance of current image format choices.
GLOSSARY
Related terms
performance
WebP (SEO)
The WebP image format developed by Google — offering significantly smaller file sizes than JPEG and PNG at equivalent visual quality — which improves page loading performance (LCP in particular) and is supported by all modern browsers, making it the recommended image format for web images.
Read definition →performance
LCP Image
The image element identified by Chrome as the Largest Contentful Paint (LCP) candidate on a page — the largest visible image in the initial viewport that determines the LCP timing score, typically the hero image, product thumbnail, or featured photo at the top of the page.
Read definition →performance
Image Compression (SEO)
The process of reducing image file sizes through lossy or lossless compression algorithms — directly impacting page load speed, LCP times, and Core Web Vitals — and the SEO implications of image compression choices for page performance and ranking.
Read definition →performance
Performance Budget
A predefined set of constraints on web page performance metrics — such as maximum JavaScript bundle size, maximum LCP time, or maximum total blocking time — used to prevent performance regression as a website evolves, by alerting or failing builds when the page\'s performance metrics would exceed the defined thresholds.
Read definition →performance
Product Image SEO
Optimisation of product page images for search engine discovery, crawlability, rendering performance, and Google Images visibility — including image schema markup, file format choice, alt text, lazy loading strategy, and Core Web Vitals impact of hero product images.
Read definition →See how your site scores on AVIF (SEO).
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