This is not specific, but may help as a pointer,
this may be the reason?
below taken from a Google search, original post link and credits below.
Volkswagen album art using CMS
August 23, 2016 in
album art by
Dan Gravell
This week I'm looking at another in-vehicle entertainment system; Volkswagen's CMS (
Composition Media System). Like
other systems, CMS is able to play music from a connected device. And also, like other systems, CMS sports a large 6.5″ display which can be used to show the album artwork that relates to the albums in your music library.
Why should album artwork be important? Well,
there are a number of reasons, but suffice to say it makes music easier to find, and more enjoyable when you can take in the artwork known to be attached to the music. It makes music a multi-media experience!
All music players, whether in your car, on your phone or in your living room, have rules by which they find and display album artwork. They need to know where to look in your music collection, and the images that are the artwork must themselves obey certain constraints, depending on the music player. For example, there may be a maximum size for the images.
CMS album art rules
CMS is no exception, and it mandates its own rules as to how album artwork should be located and the rules it should obey.
I did some Web research and these rules are:
There is some disagreement about the maximum resolution. I have seen
some suggestion that the upper limit may be as low as 400x400. I'd advise you to go with 500x500 and only revise down if you experience a problem.
There's been some suggestions that PNGs are not supported. It has since been found that
it is not PNGs so much that are the problem, but the size of the PNG file. So long as you keep under the 200Kb limit, you should be ok.
There's also suggestion that
the set of characters permitted in file names is a little narrow. Also,
hidden files can sometimes cause problems. Some other things to consider.
Bluetooth album art is not supported. In the current versions of CMS you must use a SD card to display album art.
The guys goes on to explain how to use BLISS to fix his Library Artwork, see link below.
source:
Volkswagen album art using CMS
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