"Conversion failed. The transcoder failed to start up." message when trying to play videos with external subtitles

Plex Media Server
,
12

I’m running the same setup as you, Win 10 + Synology NAS. It does fix the subtitle/transcode issue.
What you have to do is:

  1. Mount your media share as a drive (e.g. Z:)
  2. Change your libraries to use this path instead
  3. Scan your libraries to pick up the “new” media
  4. Update all metadata on all libraries

I also set up a small batch script to automatically mount the share to Z:\ when the computer starts, otherwise PMS complained that the drive was not available after a reboot.

net use Z: /delete
net use Z: \\10.0.1.35\Media /user:<user> "<pass>" /persistent:yes