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Packages available in AUR
Plex Media Server (PMS)
Install the package from AUR: AUR.
To start plex, run sudo systemctl start plexmediaserver. Use sudo systemctl enable plexmediaserver to have it start on startup. Then go to localhost:32400/manage to set up plex. If you want to add media folders in your home directory you may get a permissions issue. chmod 775 ~/ and usermod -a -G users plex to allow plex to access your files.
Plex Home Theater
It is highly recommended to install using a clean chroot (https://wiki.archlinux.org/index.php/DeveloperWiki:Building_in_a_Clean_Chroot). Install the package from AUR: AUR.