.cmap files

[newbloke]

I noticed that recent Backups have a new folder CMAP under MAKEMKV and this in turn contains a number of files with the extension .cmap.

Does anyone know why this has been added and the purpose of the files?

[mike admin]

These are created when you make a decrypted backup. They contain certain metadata that is otherwise lost when M2TS files are decrypted, which in turn is needed for a correct BD-J emulation off the decrypted backup folder. Newer versions of BD-J protection use M2TS files as a decryption key, so if M2TS file is decrypted without CMAP (by older version of MakeMKV for example) then BD-J protection code becomes cryptographically impossible to emulate.

[MKV Maker]

For the first time ever today I encountered the .cmap files. I downloaded an entire BD-ROM UHD and inside of the folder is a MakeMKV folder with subfolders AACS and CMAP. Is any of this useful? I copied all titles successfully without any of it. If no then why is it there? If yes then how to make use of this data?