JPEG to AVIF Converter: Lossless In-Browser Re-Encode

AVIF is a still image wrapped in the AV1 video codec, published by the Alliance for Open Media as a royalty-free answer to HEIC. People who already shipped JPEGs reach for it for two reasons: AV1's intra-frame compression beats JPEG at the same visual quality, and every current browser engine (Chrome, Firefox, Safari 16+) decodes it without a plugin or license fee. This page does one specific job: it takes an existing JPEG and re-writes its pixels into an AVIF file without adding a second round of lossy compression. Mechanically, the browser decodes the JPEG through its native image pipeline (createImageBitmap), draws it to an OffscreenCanvas, and reads back the raw RGBA pixels. Those pixels go straight into @jsquash/avif, a WebAssembly build of libavif, encoding at effort 6 with lossless turned on. Lossless here means relative to the decoded bitmap: every pixel the JPEG renders to is preserved bit for bit in the AVIF. No new quantization, no extra blocking, no chroma smearing layered on top of what the JPEG already had. That design has a consequence worth stating up front: because your JPEG was already compressed lossily, a lossless AVIF re-encode bakes in the existing JPEG artifacts and usually will not shrink the file. On photographs a lossless AVIF often lands near the JPEG's size or above it. The dramatic AVIF size wins you read about come from lossy encoding at a target quality, which this tool deliberately does not do. Use this when you need the image inside an AVIF without degrading it further; use a lossy AVIF or WebP encoder when a smaller download is the actual goal. Nothing leaves the tab. The decode, the WASM encode, and the download all run on your machine, and the image is dropped from memory when you close the page.