I’m looking into the same thing myself. I actually got an RPi for just this purpose, but then I discovered volumio and I’ve been sidetracked. (A lot of this relies on SMB/Samba-- a widely used standard for sharing folders or drives over a network.)
A few possibilities for such a thing:
Inside your LAN
- Access Volumio’s existing SMB shares from your preferred slab of glass. There are a few apps on Android that let you do that, and I believe some for iPhones.
- Install a DLNA server on your Volumio box.
(I haven’t looked into these much-- when I’m on my own LAN, I’ll be using Volumio’s standard music player).
Outside your LAN/Over the Internet
Set up a VPN to your home network, and use SMB shares as above. I tried this, and I’m not happy with it-- VPN’s tend to be slow, and running one through a residential internet connection is painful
Make your SMB viewable from the internet-- BAD idea. Huge security hole.
SSH tunnel for an SMB share-- theoretically possible, but I’ve not found an easy way to deploy it.
SFTP - Rather clunky.
Seafile or similar DIY cloud package-- All of these tend to set up their own filesystems, that don’t play well with Volumio. I want one set of music files to run through volumio or remotely.
(Everything over the internet requires some sort of way for your to find your home network, like a DDNS service)
The ability to access my music library over the internet is a big thing for me. None of the options I’ve found are satisfactory; I’ll keep looking into it.