Mediafiles on synology nas not added in library

You are still not following Plex’s naming convention.

As @dbirch mentions, you must put TV shows in TV show libraries for them to be recognized. Also, movies must be in a movie library. Plex does not support mixing movies and TV shows in the same library.

What show is that? Is it this one: Power?

If it is, the correct naming and organization is:

/volume1/Plexmedia/TV Shows <-- Folder added to TV show library (name not important)
.../Power (2014) {tvdb-276562} <-- ShowName (Year); TVDB/TMDB ID optional
....../Season 05 <-- "Season" in English; Two digits for number
........./Power (2014) s05e02.mkv <-- sXXeYY format mandatory
  • Read and follow Plex’s documentation. Use the links provided above.
  • Rename your files accordingly
  • Plex Dance the show after making corrections. This removes any incorrect matching information from the Plex Media Server database.
  • Tiny Media Manager, mentioned by @dbirch, is a very nice tool, and can help with your renaming. The free version works well, and can help with both movies and TV shows.