Without ItemKey::Unknown what is the best way to add custom fields now?

[UnknownSuperficialNight]

In my metadata editor I had a generic function to help insert some custom fields in particular:

COUNTRY, COUNTRY-OF-ORIGIN or RELEASECOUNTRY
TAGS (For undefined sorting example I tag music from games with the GAME tag this was if I want gaming related music it's easy to find)
etc...

So for adding these in what is the best way previously I used this:

/// Helper function to insert custom metadata fields
fn set_custom_field(tag: &mut Tag, field_name: &str, value: &str) {
    let item_key = ItemKey::Unknown(field_name.to_string());
    if value.is_empty() {
        tag.remove_key(&item_key);
    } else {
        // Create a TagItem with the custom field
        let tag_item = TagItem::new(item_key, ItemValue::Text(value.to_string()));
        // Use insert_unchecked for custom fields
        tag.insert_unchecked(tag_item);
    }
}

[Serial-ATA]

There's no way to add custom fields without using the concrete formats like Id3v2Tag. ItemKey::Unknown was kind of a nuisance since it required Lofty to do extra validation when merging tags. With it gone, every ItemKey is now guaranteed to have well defined mappings.

It also pushes users away from resorting to custom fields unless absolutely necessary.

What I recommend instead is to make PRs for any ItemKeys that you may need. For example, release country is already a well defined field, it just doesn't have an ItemKey mapping yet: https://picard-docs.musicbrainz.org/en/appendices/tag_mapping.html#id30

As for TAGS, that'd probably be better suited for an ItemKey::Keywords (which also doesn't exist, yet).

[UnknownSuperficialNight]

Thank you, I made a PR to get ReleaseCountry in ItemKey

Out of curiosity, what do you plan ItemKey::Keywords to do?

[Serial-ATA]

There's no standard for keywords, but it looks like it's typically just a single string of words separated by ", " (e.g. 80s, disco, ...).

As for what they map to, here's what I found:

• MP4: keyw (maybe also ©key??) (https://kodi.wiki/view/Video_file_tagging)
• ID3v2: TKWD (maybe also TXXX:KEYWORDS??)

So for those two I guess just map all of them.

Then for Vorbis Comments and APE, it could just be KEYWORDS.