Innuos Sense 26 (currently in Beta) introduces support for classical music metadata. It now shows correctly Works and titles (discussion ongoing about showing Movements) information about orchestras and conductors etc.

One issue is with ALAC files (and presumably AAC) for conductors:
Yate maps Conductor in MPEG-4 to ----:com.apple.iTunes:CONDUCTOR (read fallback Conductor). It has no mapping for the short atom ©con, which Innuos Sense writes and reads — Yate shows it in the Unhandled panel.
Two requests:
1 Read ©con into the Conductor field, and ideally write it alongside the freeform atom.
2 More generally: the Custom Field Editor's "MPEG-4 ---- atom name" box can only name a freeform atom inside a ---- wrapper. There's no way to define a custom field targeting a standard 4-character atom. Typing ©con there produces ----:com.apple.iTunes:©con with the © as two UTF-8 bytes (C2 A9) — silently useless, and it looks plausible in the UI. Either allow a standard atom to be specified, or reject/warn on a non-ASCII atom name.

1 Read ©con into the Conductor field, and ideally write it alongside the freeform atom.

I've implemented support for the ©con atom. Your can choose to write any of CONDUCTOR, Conductor or ©con. You can choose to read all. I'm loathe to write multiple encodings of a tag as getting out of sync is always an issue when other taggers are involved.

2 More generally: the Custom Field Editor's "MPEG-4 ---- atom name" box can only name a freeform atom inside a ---- wrapper. There's no way to define a custom field targeting a standard 4-character atom. Typing ©con there produces ----:com.apple.iTunes:©con with the © as two UTF-8 bytes (C2 A9) — silently useless, and it looks plausible in the UI. Either allow a standard atom to be specified, or reject/warn on a non-ASCII atom name.

The Custom Field Editor only allows for the creation of ----:com.apple.iTunes: form atoms in MPEG-4 atoms. Entering an © is unusual but perfectly valid. If we implement the ability to specify four character atom codes, there'll be a means of explicitly specifying the atom. However, additional information will have to be provided such as numeric or text, etc. As far as issuing a warning, any UTF8 character is supported. This has never come up since 2012 🙂

The ©con support will be in Yate v10.0.