Cover art not shown from embedded tag (from iTunes)

[danosavi]

Hi, I've just set up my SS server (on linux xubuntu), and it works except it shows just few of the albums covers. All the covers were embedded in the same way (using iTunes) and all the songs are in the same format (m4a AAC), so I can't find a logic why some album covers are shown and some not.

I noticed there's a way to manually change (and harvest from Google) cover arts, which is cool, but with 400 albums it's...well, something I would do only if there's nothing else possibile

Has someone any hint to solve this issue? Thanks