The short answer: you do not have to choose only one
AVIF and WebP are both efficient web raster formats. The better choice depends on the image type, browser audience, and delivery pipeline.
The most resilient strategy is content negotiation, not a one-format migration: serve AVIF when supported, WebP next, and JPEG or PNG as the final fallback.
The key differences between AVIF and WebP
AVIF uses the AV1 codec and often produces smaller files at a similar visual quality. Its advantage is especially visible in photographs, gradients, and dark scenes.
WebP supports lossy and lossless compression, transparency, and animation, with a mature browser and tooling ecosystem. It is a strong default when predictable delivery and fast encoding matter more than the smallest possible file.
- AVIF: generally better compression, higher encoding cost, and a stronger need for fallbacks
- WebP: small enough files, fast processing, broad compatibility, and operational simplicity
| Criterion | AVIF | WebP |
|---|---|---|
| Compression | Usually stronger | Strong |
| Encoding speed | Relatively slow | Relatively fast |
| Transparency and animation | Supported | Supported |
| Operational complexity | Needs fallback and encoding review | Lower |
| Recommended default | First candidate for photos and large images | Reliable general-purpose default |
A decision guide by situation
For photo-heavy content sites and product pages, test AVIF first. Do not optimize only for bytes: compare AVIF, WebP, and JPEG side by side from the same source.
For logos, icons, and UI screenshots where transparency and crisp edges matter, start with lossless WebP or SVG. Compression artifacts are especially harmful when images contain text.
How to declare a fallback with `<picture>`
A browser may fail to render an unsupported format. Put sources in AVIF → WebP → JPEG or PNG order inside `<picture>` so the browser selects the first format it understands.
Provide multiple widths in `srcset` and describe the rendered width with `sizes`. Changing the format alone will not fix an oversized source image.
<picture>
<source
type="image/avif"
srcset="hero-640.avif 640w, hero-1280.avif 1280w"
/>
<source
type="image/webp"
srcset="hero-640.webp 640w, hero-1280.webp 1280w"
/>
<img
src="hero-1280.jpg"
srcset="hero-640.jpg 640w, hero-1280.jpg 1280w"
sizes="(max-width: 768px) 100vw, 70vw"
width="1280"
height="720"
alt="제품을 사용하는 장면"
/>
</picture>Measure the user experience, not the format
File-size reduction is only one metric. Track the actual transfer size of LCP images, decode time, encode time, cache hit rate, and image failure rate.
‘Same quality’ varies by tool and image. Build a representative sample set, keep encoder settings documented, and combine visual review with network measurements.
Pre-release checklist
- ✓ Is the original JPEG or PNG stored separately?
- ✓ Were AVIF and WebP compared from the same source?
- ✓ Are `srcset` widths aligned with mobile and desktop render sizes?
- ✓ Does the AVIF → WebP → JPEG or PNG fallback work?
- ✓ Were LCP, transfer size, and decode or encode time checked before and after release?
- ✓ Did a person review text, logos, and transparent areas visually?
Frequently asked questions
Is AVIF always smaller than WebP?
No. Results vary by image content and encoder settings. Compare real files from the same source at a similar visual quality.
Is WebP alone enough?
For many services, yes. WebP alone is reasonable when simplicity, tooling compatibility, fast processing, and predictable fallback matter.
Is one format better for SEO?
Do not treat the format itself as an SEO score. Focus on the right dimensions, descriptive `alt`, appropriate lazy loading, and layout stability.