How to: Convert Windows M4A file rating

[DetlevD]

@disfunktor

Recently, I started to convert my music archive to M4A instead of MP3 as I did for many years before. I always used the Windows File Explorer to rate the songs in the 5 star rating system. This translated well, and was visible in Winamp for Windows, and my mobile music player of choice which was obviously using the same system of rating. ...

I do not know for sure, what you have to do in your case, so ...
... a media file, tagged with the ID3v2.3/4 system (maybe other tagging systems too), ...
can hold one or more tag-fields for each rating method side by side in the tag, technical frame name is "POPM", ... custom names are RATING MM, RATING WMP and so on, ...
the name depends on the applied rating software.
You have to find out, if only the name of the tag-field has to be changed, ...
or if you simply have to copy the one RATING XXX to a new tag field RATING YYY, ...
or if you indeed have to convert the technical rating values from one measurement system to the other.

@disfunktor

However, few weeks into creating an M4A archive, I just realized that the 5 star rating for M4A that I do in Windows (8.1) File Explorer, do not translate to Winamp type of 5 star rating. And now I'm stuck with a huge amount of unrated songs in players.
Is there a way to convert the File Explorer rating to the classic 5 star rating visible in Winamp? I see that there is a Convert>Tag-Tag option, with 3 types of rating inside, but I can't figure out how to convert the rating tags. Can someone please help?

Which rating related tag-field custom name do you see in the Mp3tag dialog "Extended Tags..." for a rated M4A file, technical frame/atom name is "rate", which you have rated in Windows 8.1?

See also ...
/t/15671/1
http://forums.winamp.com/showthread.php?t=376798

DD.20150122.1100.CET