It does not maintain the JPEG format, tho it will be part of the JPEG XL format. It is repacking/recoding jpegs in a lossless and reversible manner, so that cl

It does not maintain the JPEG format, tho it will be part of the JPEG XL format. It is repacking/recoding jpegs in a lossless and reversible manner, so that clients supporting brunsli can be served directly with the optimized version (their apache and nginx modules seem to serve files with a image/x-j mime), and clients without support can be served with the original jpeg file (or served with a brunsli file and decoded with a wasm-brunsli->native jpeg decoder pipeline if wasm is an option), while you only have to keep the brunsli (or original jpeg) file around. Since JPEG XL isn't finished yet, there still might be minor differences in the end that make the current brunsli format incompatible to the JPEG XL format, so I wouldn't mass-convert your files just yet.