Where AVIF files come from and why they cause trouble
AVIF is an image format built on the AV1 video codec, published in 2019 by the Alliance for Open Media. It stores a still picture as a single compressed video frame, which is why it is so efficient: a photo that needs 400 KB as a good JPG often fits in 100 to 150 KB as AVIF with similar visible quality.
You usually end up with AVIF files without asking for them. Image CDNs and many large websites serve AVIF to any browser that announces support, so "Save image as" in Chrome or Firefox often gives you a .avif file.
The trouble starts outside the browser. Older versions of Windows Photos, Microsoft Office, many print kiosks, government upload forms, older Photoshop and Lightroom releases, and most messengers either refuse AVIF or show a blank thumbnail. JPG, standardised in 1992, opens in practically everything, which is the whole point of converting.
What happens to your image during conversion
The conversion runs in your browser. The browser's own AVIF decoder turns the file into raw pixels, those pixels are drawn on a canvas at their original width and height, and the canvas is encoded as JPG with the quality you choose. When the browser allows it, this happens in a background worker so the page stays responsive during a large batch. Nothing is sent to a server.
A few details matter here:
- Dimensions stay the same. A 2400×1600 AVIF becomes a 2400×1600 JPG. If you also need a smaller picture, run the result through resize image.
- Transparency is flattened. AVIF supports an alpha channel, JPG does not. Transparent areas are filled with the background colour from the picker, white by default. For a logo you plan to place on a dark page, pick that page's colour instead of white so the edges blend in.
- Animated AVIF gives one frame. AVIF can hold image sequences; only the first frame is converted.
- HDR and wide colour are reduced to standard range. AVIF can store 10- and 12-bit HDR images. The canvas works in 8-bit sRGB, so HDR pictures are mapped to normal brightness and the output carries no embedded colour profile. Ordinary web AVIFs are already 8-bit sRGB and are not affected.
- Metadata is not copied. The JPG is encoded from pixels, so EXIF and XMP data in the AVIF are left behind.
Choosing a JPG quality setting
The slider runs from 10% to 100% and starts at 90%, which is higher than the 85% used by most of the other JPG converters on this site. The reason is that AVIF images have usually been compressed hard already. Their typical artefacts are smoothed textures and slightly soft edges rather than JPG's blocky noise, and re-encoding at a low JPG quality stacks a second kind of loss on top of the first.
Practical starting points:
- 90% for photos you will view, share or print. The result is close to what the AVIF showed.
- 95–100% if you will edit the image further and save it again, or for screenshots and graphics with small text.
- 75–80% when the JPG has to stay under an upload limit, such as 1 MB on a form. Check the size shown next to each file after conversion.
Why the JPG is bigger and what to do about it
Expect the JPG to be noticeably larger than the AVIF. The per-file summary shows the original and new size side by side, and a 120 KB AVIF turning into a 350 KB JPG is normal. This does not mean quality was added; it only means JPG needs more bytes to describe the same pixels.
If the size matters:
- Lower the quality slider in steps of 5 and compare. Most photos look unchanged down to about 80%.
- Reduce the pixel dimensions. A 4000 px wide image shown in a 1000 px slot wastes three quarters of its data.
- For final tuning, compress the JPG afterwards with a target that suits the destination.
Browser support and limits
Because decoding relies on the browser, you need one that reads AVIF: current Chrome, Edge, Firefox and Opera all do, and Safari does from version 16.4 on macOS and iOS. If a file fails to decode, the cause is most often an outdated browser, a file that is not really AVIF despite its extension, or a damaged download. If the browser cannot display the file in a tab, it cannot convert it either.
Each file can be up to 50 MB. You can drop many files at once; they are processed one after another with the same quality and background settings, then downloaded individually or as a single ZIP.