I have installed LibreELEC Kodi on a RPi 4 and everything works well on the Host. I am using the MariaDB/MySQL server add-on to store the Music Library. The main reason for this is so that the information can be shared by an Amazon Fire TV Stick connected to my television.
After considerable helpful advice from Kodi Forum Members (see my Post "Newbie's First Kodi System"): I have managed to navigate the Library on my TV, listen to music files, and view text contained in artists' NFO files. Unfortunately, no associated artwork appears.
I have Samba shares for two Music sources : 'Artist Music' and 'Compilations' on the RPi 4. These are accessible from Windows Explorer on my Windows 10 desktop computer. MySQL Workbench is able to examine the MariaDB data tables. Here are a few edited lines from the 'art' table:
Network Share
'album', 'thumb', 'smb://192.168.0.16/Maxtor 1/Artist Music/Christopher Hogwood/Clarinet Concerto Oboe Concerto/folder.jpg'
'album', 'thumb', 'smb://192.168.0.16/Maxtor 1/Artist Music/The Linsdale Singers/40 years in 140 minutes CD1 1977-2001/folder.jpg'
'album', 'thumb', 'smb://192.168.0.16/Maxtor 1/Artist Music/The Linsdale Singers/40 years in 140 minutes CD2 2002-2017/folder.jpg'
Local File
'artist', 'thumb', '/var/media/Maxtor 1/Artist Information/Christopher Hogwood/folder.jpg'
'artist', 'fanart', '/var/media/Maxtor 1/Artist Information/Christopher Hogwood/fanart.jpg'
You will see that the Album Art is referenced using smb:// network paths. These allow the Amazon Fire TV Stick to display the artwork (thanks to the advancedsettings.xml file!). The text information for the individual artists is stored in the MariaDB database directly. The Artist Art is, at present, referenced using a local file situated on the same USB 3 drive (Maxtor 1).
I reasoned that if I could reference the Artist Information folder as a shared folder I should be able to get the artist artwork to appear on the Fire TV Stick.
I have checked that the Artist Information folder is indeed shared correctly. It exists; and is readable/writeable from Windows Explorer and WinSCP. Using PuTTY, I have examined the directory permissions. They are: drwxr-xr-x (755). The owner is 'root'.
I believe that Music Sources and File Sources are handled separately in Kodi. I used Settings>Music>Artist information folder to browse for the Artist Information folder. The Browse for Folder screen showed the expected local path (see above) , namely, /var/media/Maxtor 1/Artist Information.
However, I wished to use a networked path, so I selected the New folder option and entered 'smb://192.168.0.16/Maxtor 1/Artist Information/'. I obtained the following error message:
"Couldn't create folder. Make sure the selected folder is writeable and that the new folder name is valid''. The folder already exists. Why does Kodi need to create it?
I did, temporarily, try the dreaded 777 permissions; but that made no difference. Could it be an ownership issue or something similar? I am now confused! 
