AOMedia Video 1 (AV1) is an open, royalty-free video coding format designed for video transmissions over the Internet. It was developed as a successor to VP9 by the Alliance for Open Media (AOMedia) [...] The AV1 Image File Format (AVIF) is a specification for storing images or image sequences compressed with AV1 in the HEIF file format.[121] It competes with HEIC which uses the same container format, build upon ISOBMFF, but HEVC for compression.
-https://en.wikipedia.org/wiki/AV1
It offers superior compression ratio and image quality even compared to WebP. I use it with a small polyfill on my blog https://github.com/Kagami/avif.js
It's the new cool image format on the block and browsers are starting to support it (https://caniuse.com/#feat=avif). The video format it is based on is already pretty widely supported across the browsers: https://caniuse.com/#feat=av1
It offers superior compression ratio and image quality even compared to WebP. I use it with a small polyfill on my blog https://github.com/Kagami/avif.js
Multiple AVIF Encoder/Decoders are available (for SDWebImage) https://swiftpackageregistry.com/search?topic=avif