I finally got all my music in FLAC format to display album cover artwork in Groove on my desktop Windows 10 system, after many hours of trial and error.
I have over 1400 albums and it took hours and hours to get there, by adding 7 albums at a time.
I use FLAC with album art at 500x500 embedded in the track files. Tag data edited by the excellent MP3Tag. The files are not held under my windows profile, but on another local disc drive. There are 5 folders each holding 300 albums.
After the recent update I noticed just a few of my albums were displaying cover art correctly. So, I did more testing, adding just a few albums at a time, and it worked.
There was nothing wrong with the tags in my files. On my system, it was about how many albums are being adding in one go. When I add up to 7 albums it usually added the artwork after a few seconds.
The process that worked for me was: Start by adding my first folder, holding 300 album folders. Groove then loads the 300 albums, all but a few with no artwork. Then, delete the first 7 album folders using file explorer, restart Groove, wait for Groove to
remove the same 7 albums, undo the delete, restart Groove again and wait for Groove to add the same 7 albums, this time with artwork.
Repeat for the next 7 albums until that folder is done and all 300 albums show artwork in Groove. Then add the next 300 album folder and repeat again untill all folders have been added.
It's important to restart Groove after each change as it doesn't remove or add albums otherwise.
If you add more than 7 albums the chances are Groove will then persistently fail to pick up the artwork when it re-adds them. In those cases I copied the album folder to somewhere else, deleted the original and copied back in. I think this worked because
the time stamp of the files changes.
Sometimes it didn't pick up the artwork for all 7 of the newly re-added albums straightaway. It would get a few within a few seconds, then a few more after a few more seconds.
Some it would not get until you had moved on to the next 7 and deleted the folders of the next 7. When Groove removed the next 7, after a few seconds, the missing art from the previous 7 would appear.
The process gradually got slower as the number of albums increased. At first, it took Groove about 60 seconds to recognise when album folders had been deleted, by the end it was up to about 3 minutes.
I also tested with other locations. If I did this under My Music under my user profile on the system disk (C:) it was much faster, cutting Groove's time to detect removal or addition of folders (albums) to just a few seconds.
A possible way to speed up the process is to start with an empty folder and gradually copy in your FLAC albums up to 7 at a time.
As well as watching Groove to see if the artwork is added you can also monitor the contents of this folder:
C:\Users*<your user name>*\AppData\Local\Packages\Microsoft.ZuneMusic_8wekyb3d8bbwe\LocalState\ImageStore
Groove adds a file like this "NS_40nSLKDoXeUUq6q5TtRAK9rVyvpbGrq5nIVw3yo_0_0" with a random name for every artwork Groove finds. It's actually a 320x320 jpeg of the artwork found. If all goes well, this folder will contain 1 file for every album in Groove.
Groove still doesn't pickup any artist pictures, but I guess that's because I have set Groove to not automatically update from the internet. I don't want my collection of ripped CDs, carefully built up over many years, to be overwritten.
Hope that helps! Now to see if I can get my m4a (AAC) files to load...