Where a PNG to AVIF conversion pays off
PNG is the format things get exported as — screenshots, design exports, logos, diagrams — and it is lossless, which means it stores every pixel faithfully and grows large doing it. A single full-screen capture can run to several megabytes. AVIF was built for the opposite priority: it is a modern web image format designed to carry the same picture in a fraction of the bytes. If those PNGs are headed for a website, an app bundle, or anywhere page weight is counted, AVIF is usually the largest single saving available, and it keeps the transparency your PNG carries.
The first conversion is the slow one
AVIF is the one output here that your browser cannot encode on its own. This page uses a WebAssembly encoder — roughly 3.4 MB — fetched from this site the first time you convert to AVIF and cached by your browser afterwards. Expect a pause before the first file completes, then normal speed. Even warmed up, AVIF is by a wide margin the slowest encoder in this converter, so a large batch is worth starting and leaving alone. Three files are processed at a time, and results download one by one or as a single ZIP.
What you give up
AVIF output here is lossy. The decoded pixels of your PNG are re-encoded at a high quality setting rather than stored exactly, so the result is not a pixel-for-pixel copy — keep the PNG if it is a master file, an archive, or artwork you plan to edit again. Compatibility is the other consideration: every current browser displays AVIF, but desktop photo viewers, older editors, and plenty of upload forms still do not recognize it. AVIF is a good final format for the web and a poor one for sending a file to somebody who just needs to open it.