This openly-documented binary file format [1] is widely used for encapsulation and compression of digital computer files. Use of an operating system decompressor is recommended to access files stored in this format.
References
[1] International Organization for Standardization, “International Standard ISO/ IEC 21321-1, Information technology — Document Container File — Part 1: Core, First Edition” (2015). Online: http://standards.iso.org/ittf/PubliclyAvailableStandards/c060101_ISO_IEC_21320-1_2015.zip; accessed May 12, 2017