glynor,
As you probably know I use a similar system for copying the library files and the thumbnails between the PCs.
In any case, I wouldn't label the MPL stuff as weird. A library copying system works only for complete libraries if all files are shared. It is not usable for merging partial libraries like MPL is or for doing what Doof explicitly requested:
What I really need is some way that MC could store the video tags externally
However, a library copy system would probably be better for Doof if he has all library files on the other PC, i.e. the local library is not a combination of local files and network files.
So if I'm understanding correctly, what I should do, is, in the import settings, to disable all file types on my Videos folder except for MPL. Then whenever I add video files to my library, do my tagging, then export a new MPL file (presumably with a different name so that Otto on the HTPC will grab it?) and everything on the HTPC should have the same data.
What about if I just change tags on the main PC? From what you describe, those changes won't make it to the HTPC's library, even if I do export a new MPL file, correct?
I have not actually tried MPL import with Otto. I assume that it is intended to work similarly like it works with MC11.1's import dialog. That is what I described.
Working with MPL files is quite manual, but as I said it is the only way to partially merge separate libraries.
I would gather the new video files in a playlist and after tagging them I would export the list in MPL format and clear MC's internal list.
I would avoid importing the files on the other PC before they are tagged and the MPL playlist is available.
Before that I could still play the unimported video files directly in Playing Now without tags. Though, MC keeps the PN files in its internal PN database until PN is cleared from these files and MC is restarted. So in this case it is needed to clear the list and restart MC before importing the MPL file.
Edit
Actually, I would probably use VLC, Media Player Classic, WMP or a similar program for a quick video playback before the files are imported to MC.
Edit 2
The only way to update old file info with an MPL file is to remove the files from the library first.