This format is create by BYUU for archiving cd base media (CDA/CD-rom/etc but not (HD)DVD nor Bluray disk for now) that preserve subshannel data.
artical by byuu: https://byuu.net/compact-discs/structure
code (ISC license): https://github.com/byuu/bsnes/tree/master/nall/cd
Licents txt: https://github.com/byuu/bsnes/blob/master/LICENSE.txt