Tvheadend

Hi,

I have a Synology DS412+ with TVHeadend (4.4.20181215) installed. Due to a crash I had to re-install DSM (DSM 6.2.2-24922 Update 4) and TVHeadend.

I see some strange behaviour which might have to do with access rights so I'm looking into permissions.
I'm not sure whether I need to use a local user or a system internal user account?

I have both:
- Local user: tvheadend-testing
- System internal user: sc-tvheadend-testing

Furthermore I read about sc-download and sc-media.
Anyone knows how these pieces fit together?
Any articles online?