In this previous post I explained the good news for Classical music fans that iTunes now has support for works and movements. But the bad news for Mp3 and Aif formats was that it was now using the TIT1 field to store the Work instead of the Grouping. This meant the Grouping field could only be set within iTunes and was stored in the database.
I have just installed iTunes v126.96.36.199 and this has changed.
iTunes has now added a GRP1 field for formats that use the ID3 metadata format such as Mp3 and Aif formats. The good news is that now you can set the Grouping and Work fields from outside iTunes by writing data to the GRP1 and TIT1 fields respectively.
But the bad news is that ever other player out there uses TIT1 for grouping so if grouping is important to you and you need to play your songs on iTunes and other players you have a problem.
Because if you set the Work field in iTunes, this will be seen as the Grouping field in other applications. If you set the Grouping field in iTunes this will have no affect in other applications because they don't support the new GRP1 field
It would have been infinitely more sensible for iTunes to leave the TIT1 field alone and define a new field to store the Work