This mpv.conf
consist of subtitle style configuration for Plex Media Player only, you could save the file into folder below, then restart your Plex Media Player aplication.
- Windows:
C:\Users\USERNAME\AppData\Local\PlexMediaPlayer
- OSX:
~/Library/Application Support/Plex Media Player/
- RPi2/OpenELEC:
/storage/.local/share/plexmediaplayer/
The screenshot are taken on Windows 10.