Question about the rating field

[UnknownSuperficialNight]

Hi I've been trying to make a "Rating" field to store the rating of a song, however there seems to be some custom logic somewhere as when I edit the "Rating field":

/// 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);
    }
}

set_custom_field(tag, "RATING", &value.to_string());

This seems to instead of overwriting the rating field or removing it, it seems to append

Using mediainfo I've found previous values there

Rating                                   : 5 / 9 / 6 / 1

So what is so special about this particular key?

Note: my test format is opus thus it should be VorbisComments

[Serial-ATA]

Hello!

So this is an interesting one. First of all, the ItemKey variant you're looking for is ItemKey::Popularimeter, which maps to "RATING" for Vorbis Comments. When a VorbisComments tag gets converted to a Tag, all of its keys will be translated to an ItemKey. So, when you initially write your custom ItemKey::Unknown("RATING"), it will get written to the tag normally, but be re-read as ItemKey::Popularimeter not ItemKey::Unknown("RATING"), these are two different things. Tag::insert{_unchecked} will check if the ItemKey matches an existing one in the tag, and since those two are different, you'll always fail that comparison and instead append an additional item to the Tag.

In your case, you can fix this by simply changing to ItemKey::Popularimeter. I'll likely remove ItemKey::Unknown sometime in the near future. It's confusing that it can't be compared to pre-mapped keys.

[UnknownSuperficialNight]

Thanks a bunch, I figured it was being mapped to something else

Without ItemKey::Unknown how would people insert custom non-standard metadata fields in the future?

[Serial-ATA]

ItemKey::Unknown was kind of a hacky way to retain tags that couldn't be mapped to concrete ItemKeys. There have been alternatives for awhile now though, with SplitTag, MergeTag, and GlobalOptions::preserve_format_specific_items() (see #302 for more info on that).

I envision people taking their Tags, converting them to a concrete format (e.g. VorbisComments), and then adding their custom fields to that. I'd rather not have a way to generically add custom fields, since the mappings for the concrete ItemKey variants are known to be valid, but with Unknown, there's extra verification that needs to be done on conversions that could be skipped if I just get rid of it entirely.

You'd go from:

tag.insert_text(ItemKey::Unknown(String::from("FOO")), String::from("BAR"));

to:

let mut vorbis_comments: VorbisComments = tag.into();
vorbis_comments.insert(String::from("FOO"), String::from("BAR"));

ItemKey supports the keys that the vast majority of users will need, anything else would be niche and require a little extra effort working with the concrete formats.