Why Won't My AVIF File Open?
AVIF opens instantly in Chrome, Firefox, Safari, and Edge. Drop the same file into Photoshop, attach it to an email, or upload it to a form somewhere else, and it can just fail, no thumbnail, no preview, sometimes no error message at all. Both things are true at once because AVIF support isn't one on/off switch. It's a patchwork of separate decisions made by browser vendors, operating systems, and individual applications, all on different timelines.
Browsers solved this years ago. Everything else didn't
AVIF is an image format built on the AV1 video codec, and every evergreen browser added a built-in AV1 decoder specifically to support it. That's why a webpage using an AVIF image just works, the decoder ships inside the browser itself, with no extra install and no user action required. Operating systems and desktop applications don't get that shortcut. Each one has to add AVIF decoding on its own schedule, and most of the software people already have installed predates AVIF entirely.
Windows needs a separate extension
Windows File Explorer and the Photos app don't ship an AV1 decoder in older builds. To get thumbnails and previews for AVIF files, you need to separately install the "AV1 Video Extension" and, in some Windows versions, the "AVIF Image Extension" from the Microsoft Store. Without both, a folder full of AVIF files just shows generic icons and double-clicking one does nothing. This is the same pattern Windows uses for HEIC: the format itself isn't broken, the decoder simply isn't bundled into the OS by default the way JPG and PNG decoding is.
Photoshop and Lightroom
Older versions of Photoshop and Lightroom predate AVIF support entirely, they were built and released before the format existed as something Adobe needed to handle. Even on versions that do support it, AVIF import was added later than most other formats, so a Creative Cloud install that hasn't been updated in a while can still reject the file outright. There's no workaround inside the app in that case, the decoder simply isn't there, only updating or converting the file first fixes it.
Email and upload forms
Most email clients render attachment previews through their own older preview engines rather than a modern browser rendering path, and those engines frequently don't recognize AVIF at all, the attachment downloads fine but shows no preview and sometimes triggers an "unsupported file" warning. Upload forms have the same problem from the opposite direction: a lot of CMS platforms, government portals, and business file-upload fields still hard-code an allowlist of accepted extensions, typically jpg, png, and webp, written before AVIF was common enough to bother adding. The file gets rejected not because it's corrupt, but because the form was never told AVIF exists.
The actual rule
Use AVIF freely for anything staying on your own website, every evergreen browser decodes it natively, so visitors never notice. Treat it as risky the moment the file leaves your control and lands in software you don't choose, someone else's Windows PC, their Photoshop version, their email client, or a form with a fixed allowlist. In that case, convert first rather than finding out after the fact that it didn't open.
Convert AVIF to JPG runs entirely in your browser, so a batch of AVIF images can be converted to a format everything opens without uploading a single file anywhere.
Related guide
For what AVIF actually is and why it produces smaller files than JPG or WebP in the first place, see AVIF explained.