libavif
Library for encoding and decoding .avif files
...It supports all AV1-supported YUV formats and bit-depths, including alpha (transparency), and includes command-line tools (avifenc and avifdec) to easily convert to/from AVIF from common image formats like JPEG, PNG, or Y4M. The API is straightforward, allowing applications to integrate AVIF support natively — creating, decoding, compressing, or decompressing images programmatically. Recent developments have added experimental support for HDR gain maps, improved color-space handling (including wide color gamut and high bit depth), and better quality tuning modes for encoding, making libavif a cutting-edge tool for high-quality image compression.