Wow, that was fast. I'd prefer a rating from 0 to 100 percent in ten percent steps as in Mediamonkey.
I don't know whether there's a standard.
Edit: I only use Mediaportal and MediMonkey. Mediamonkey stores the rating to the tag. Mediaportal doesn't seem to read those ratings though.
I don't whether it discards all fields not shown in the Now plaing window.
Do you need a file in order to check the tag?
As far as i know there are 2 rating systems embedded in FLAC, one set use 0->5 the other set uses 00->100.
From an internet search
Tag&Rename 1->5 Irivium 1->5
Mediamonkey 10->100
Foobar 10->100
I think mediaportal should do the following
Importing Rating FLAC->MP Database
If rating between 0->5 then store rating in MP database as 0->5
If rating between 6->100 then divide rating by 20 (Round up) and store in MP database as 1->5
Exporting Rating from MP Database ->FLAC
Multiply MP rating by 20x then store as a rating from 00->100
PS. I'm not sure if capitalisation matters or not, but I've seen some reference the field as "rating" and others it's called "RATING" not sure if this is caps sensitive or not, and whether it should be RATING or rating. Unfortunately I don't have many .flac files to look at.
I've implemented the writing of Ratings to FLAC in the latest MPTagThat version.
So we should be able to read it in MP as well.
Just need to code it into TagReader. Let's see, if i can get it ready with the 1.3Beta