Why anyone turns a GIF into AVIF
AVIF is the still-image profile of the AV1 video codec, and it is currently the most efficient format a browser can display. A GIF is close to the opposite: a 1987 design with a 256-colour palette and a compression scheme that predates the web. When a site still serves old GIF logos, illustrations or screenshots, converting them to AVIF typically cuts the transferred bytes by a large margin without a visible change. That is the main reason this page exists: shrinking legacy assets for the web, not archiving them.
The conversion runs entirely on your device. The browser decodes the GIF, and a Web Worker encodes the result with the WebAssembly AV1 encoder from jSquash. Nothing is uploaded.
First frame only, no animated AVIF
AVIF does support animation, but this converter does not write it. The decoder hands the worker a single bitmap, which for an animated GIF is the first frame. The remaining frames are never read. If you drop a 3 MB looping clip on this page you will get a tiny still AVIF of its opening frame, and nothing else. For static GIFs the distinction is irrelevant.
What the AV1 encoder does to a palette image
The encoder receives plain RGBA pixels, so the GIF's palette origin is invisible to it. Transparency is preserved: the alpha channel is encoded as a separate plane inside the AVIF. Colour, however, is stored with 4:2:0 chroma subsampling, which is the encoder's default here. That halves the resolution of the colour information in both directions while keeping full-resolution brightness. Photographs do not suffer from this, but thin coloured lines and small coloured text, which are common in old GIF graphics, can look slightly soft or show faint fringes at the edges. Raising the quality slider reduces the effect but does not remove it, because the subsampling happens before quality is applied.
The encoder runs at effort level 4 on a scale where higher numbers are slower and slightly smaller. Effort 4 is a sensible middle ground: fast enough on a laptop, still clearly better than WebP on size. On a low-end phone a large frame can still take several seconds.
Quality settings and a worked example
The slider goes from 20 to 95 and defaults to 80. For flat graphics with hard edges, 85 to 95 keeps them crisp. For photographic GIFs, 60 to 75 is usually enough, since the source already lost most fine detail to the palette.
Consider a 800x600 screen capture saved as GIF at 600 KB. Its first frame typically becomes an AVIF of 30 to 50 KB at quality 70. The same frame as WebP at a comparable quality would be around 60 to 80 KB, and as a lossless PNG around 250 KB. A 256x256 transparent icon GIF of 12 KB usually lands at 4 to 8 KB. These are typical outcomes for that kind of content, not guarantees.
Where AVIF will not open
Browser support is now broad: Chrome, Edge, Firefox and Safari 16 or newer all display AVIF. Outside the browser it is patchier. Windows Photos needs the AV1 Video Extension installed, older macOS versions before Ventura cannot preview it, many upload forms and CMS media libraries still reject the extension, and most email clients will not render it inline. If the image is for anything other than a website you control, GIF to WebP is the safer bet, and GIF to PNG is the choice when you need an exact copy.
Keep the original GIF when the animation is the content, or when the file is a few kilobytes already. You can drop several GIFs at once; they are encoded one after another, and each AVIF downloads separately. If you are weighing formats for a whole site, WebP vs AVIF vs JPEG covers the trade-offs in more depth.