The AV1 (.avif) file format is an upcoming technology that we are very enthusiastic about. It is essentially a super-compressed image type. For its image quality to compressed file size ratio, Netflix already considers .avif superior to JPEG, PNG, and even the newer WebP image formats. The format was developed by the Alliance for Open Media in collaboration with Google, Cisco, and Xiph.org (which worked with Mozilla to create the Firefox browser). To combat the issues of licensing and open-source compliance, this format was designed to be a royalty-free and open-source image format. With AVIF, you can significantly reduce the file size of images when compared to JPEG or WebP; ~50% savings compared to JPEG, and ~20% savings compared to WebP.
TwicPics will determine the best output format for the browser issuing the request by default, but you can override this behavior using the output command line.