What you could do that would be helpful is play with folder rips on the mpv command line and figure out what params will need to be passed in. And also figure out what path needs to be passed, for example, the folder path, or the index.bdmv file, or something else, etc.
I'm looking at this and I'm not sure how this pertains to what we're trying to do. I've tried various ways, but no luck. Is this the section that we need to use?
Play data from stdin.
Play a path from Samba share.
Play a Blu-ray disc. Currently, this does not accept ISO files. Instead, you must mount the ISO file as filesystem, and point --bluray-device to the mounted directory directly.
Play a DVD. DVD menus are not supported. If no title is given, the longest title is auto-selected.
dvdnav:// is an old alias for dvd:// and does exactly the same thing.
Play a DVD using the old libdvdread code. This is what MPlayer and older mpv versions use for dvd://. Use is discouraged. It's provided only for compatibility and for transition, and to work around outstanding dvdnav bugs (see "DVD library choices" above).