[Kodi 17 Krypton] Accessing Movie library from external IP address

Hello all,

Would you please explain me how to configure Kodi to access to my NAS that accessible from an external dynamic IP ?

Let me explain that with more details.

I have a QNAP TS 251A NAS (QTS 4.3.3) with my DVD collection on it in my main house (ddns dynamic IP @)
I configured Kodi to point to my movie library and it is working fine.

I have a small appartement in another city with a Xiaomi Mi Box TV (with Kodi) connected to wifi.
I would like to configure Kodi to point to my ddns dynamic IP @.

What do I have to configure :
1) on my NAS (protocol to be used)
2) on my internet box (ports to be opened) ?
3) On my Xiaomi Mi Box TV (@ / parameters) ?

Do you know if this can be done ?

Thank you in advance.

Regards,

JC