image/jxl

The JPEG committee's designated successor to JPEG (ISO/IEC 18181), able to recompress existing JPEGs losslessly about 20 percent smaller. Its adoption story is the trap: Chrome shipped it behind a flag and then removed it, Safari added it, so feature-detect before serving. A JXL file comes in two shapes — a bare codestream starting ff 0a, or an ISO-BMFF container whose 12-byte signature is the one below — and a correct sniffer must recognize both.

Defined by JPEG XL (ISO/IEC 18181) — jpeg.org · IANA registration. Registry facts from the IANA media-types registry via mime-db.