DNLA Server not showing all Video Artwork on Clients

[kitmancraig]

I have a TeraStation 8 TB and I am trying to setup a DLNA server. I have configured the shared folder and turned on the DLNA service. I have started ripping films from my DVD collection and putting them in the shared folder. When I rip the DVDs none of the meta data is inluded so I am adding the video files to iTunes as a Home Video (MP4) and then adding the meta data manually.

This all works fine and the video files play through the clients no problem. The issue is that the Artwork I am adding to the files. Some of them show on the DLNA clients and others do not. I cannot find the reason why. I have tried size and resolution. Everything I can think of. To be absolutely sure I have tested several different clients from LG TV, to WMP and an iPhone app called UPnPExtreme. All show the same files with the same missing Artwork.

I have restarted, refreshed and everything I can think of but nothing works. It would therefore have to be the DLNA server.

Any help would be gratefully received.