It would be great to be able to filter by File Path and then create Smart Playlists for items in that/those path(s).
Why would you need to filter by file path?
You media should be organised by folder for each library, which then acts as a type of filter by file path.
Yes, but I have a nested folder for 3D in my collection. I want to be able to create a playlist of just 3D.
Well, having a nested folder is not the recommended way to set up your library. You would be better off creating a new in-bested folder for 3D movies
But then, my 3D movies would be omitted from my main collection. That won’t work.
Create a separate library in a separate folder with your 3D movies, then edit your main library to include that folder
Yes, I tried that. Then, I have duplicates of 3D content in my library. When I search, I get two and when I watch something, I have to mark it again after watching it.
I’m not sure I understand exactly what you are trying to do, but maybe this is it… :)>-
Move the nested 3D movie library out of your regular library. Update the original library, empty trash, clean bundles to get rid of anything to do with the 3D versions.
Now, create a new library that just points to the 3D versions. This is the important part… choose a different agent than the one you use for the regular library. That basically fools Plex into thinking it is a different movie. You will still get the duplicates when you search, but at the library level where all you 3D movies show, you should be able to create your playlist.
If you don’t want to have the 3D movies show up on recently added on the home page as duplicates, in the advanced options for the 3D movies, un-select “include in dashboard”
EDIT: possible that you could just use the default agent when you create the library, but just use the “don’t include in dashboard” option. I think the watched\unwatched status will bounce across between libraries that way though. Either way would create a separate library for the 3D movies so a playlist can be created.
I appreciate the suggestions, but this wont solve it either. Each of these suggestions lead to either:
a) having duplicates in search, or
b) not seeing the 3D movies in my main collection when I browse.
Filtering by path is how I accomplish this currently in Kodi, but I want to move to Plex because Kodi’s playback engine is going down hill.
just trying to help…
Not sure how you are going to get rid of duplicates in search, because there are duplicates, either as an alternate version (the 3D version) or as alternate title (as in a different library)
Another suggestion, then,
What happens if you keep the nested folder structure you have now, but create another library pointed only to the 3D movies? Use the Do not include in Dashboard option for the 3D library. Your 3D movies will be listed as their own entities in the 3D library and a playlist will be available. At the same time, the 3D versions will show up in your main library, but as duplicates (alternate versions) you can select with choose version to play.
Truth is, at the present time, I’m pretty sure there’s no way to get exactly what you want. Maybe someone has come up with a way though, be patient. 
I see what’s missing here. I don’t have a 2D version of any 3D movies.
So, it goes like this:
Library / Movies / 3D
I want to mimic how I have organized on the file level. There is only 1 copy of any movie. If I search Movies (and subfolders), I’ll get 1 match per movie. If I want to browse just 3D, I can.
In Plex, when I make my library Movies, it will include 3D and that’s great. I can search and only get 1 result per movie. However, I can’t just browse the 3D movies. So I want to make a playlist that takes into consideration the path because Plex doesn’t have a filter for 3D movies.
Early 2021 clean-up: duplicate
