NAS Media server?

[clv101]

I have a Synology DS218+ NAS, a few GB of MP3s and a Chromecast Audio. I also have a few more GB of video and a regular Chromecast on the TV. What's the best way to manage/play the tunes and video via my phone?

Plex? Is Plex free? Something else?

 

[tres]

I have exactly the same NAS.
Plex via Docker works flawlessly. I have 15tb of stuff. The ds218+ is able to transcode multiple files on the fly.
I use PlexAmp for my phone music app