I've never used custom tag field mappings much, but for 3GPP MP4 boxes and QT MOV atoms I wanted to try it.
I then realized that they are exported as part of the binary mp3tag.cfg. I'd like to suggest to export (and import) them as a plain-text .ini file in the /data folder.
This way, one could also, for instance, share settings for MediaMonkey users to support its custom tag fields:
| Tag Type | Target | Source |
|---|---|---|
| MP4 | rate |
POPULARIMETER |
| MP4 | mood |
MOOD |
| MP4 | isrc |
ISRC |
| MP4 | lyrc |
LYRICIST |
| MP4 | peop |
INVOLVEDPEOPLE |
| MP4 | otit |
ORIGTITLE |
| MP4 | oart |
ORIGARTIST |
| MP4 | olyr |
ORIGLYRICIST |
| MP4 | oday |
ORIGYEAR |
| MP4 | empo |
BPM |
| MP4 | publ |
PUBLISHER |
I would also like some explicit documentation on how Mp3tag stores custom MP4 fields (TXXX;FOO in ID3v2)): as udta.----:FOO or udta.----:com.apple.iTunes:FOO? (Also see this thread for the Mac version.)
Also related: User-defined Field Mappings