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I was wondering if it woudn't be easier to just extend the default Musicbrainz plugin instead of using the event system. Have you tried that?

@semohr I think that would be fine, I just didn't want to start by modifying the core plugin. I'm not sure how to go about the source weights though, would the distance calculation need to be modified to consider script somehow? Or how could the user nudge the proposals toward the pseudo releases?

I think that would be fine, I just didn't want to start by modifying the core plugin.

Instead, I was thinking along the lines of extending it, while keeping the logic isolated in its own plugin/file. Something like:

from beetsplug.musicbrainz import MusicbrainzPlugin

class MBPseudoPlugin(MusicbrainzPlugin):
    pass

That way, the original plugin remains untouched, and this extension can encapsulate the new behavior.
It might also be good to raise a warning or error if both plugins are enabled at the same time, just to avoid confusing overlaps.

I'm not sure how to go about the source weights though, would the distance calculation need to be modified to consider script somehow? Or how could the user nudge the proposals toward the pseudo releases?

I don’t think special handling is strictly necessary here, but I’m not 100% certain. You might want to take a look at the functions in autotag.distance.

Ah I see, I imagine that should be fine. I'm away from my pc for some time, but I'll take a look at that option.

@semohr I changed the implementation as suggested and I think it looks good. The config I mentioned in the original post still applies. I've been validating with this release and I do get the pseudo-release as the main proposal.

If this is ok, I'll add some tests and docs.

Lovely, thank you for looking into this, @asardaes, and @semohr for suggesting add_media_field. Do you want to gauge whether or not this custom tag idea is in scope for the PR? Naturally I'd welcome it, but equally I'd be happy to see the plugin be merged before going into the broader ideas of "applying metadata from multiple sources to the same file" and "tags for translations that any plugin could modify". There is also issue #2866 from 2018 which I've just discovered and reckon gets to the nub of it, with @amogus07 even currently working on a plugin with the same requirement!

Something like in my custom base class could be implemented in MetadataSourcePlugin, so plugins can like mine easily define fields in their namespace which is inferred from self.name.

Honestly, I don't care about having multiple artists, titles, etc. I just think it's useful for id fields. Everything else can be inferred from the ids by reimporting. It would also fix multiple plugins trying to override the same album or item when running beet mbsync, since they would all use different id fields.

@miblodelcarpio I added the option to only add custom tags. Since beets already supports custom path configurations, it seems this would accomplish what you wanted:

paths:
    default: %ifdef{album_artist_transl, $album_artist_transl, $albumartist}/%ifdef{album_transl, $album_transl, $album}%aunique{}/$track%ifdef{title_transl, $title_transl, $title}

@asardaes Oh wow, thank you so much! Really looking forward to giving this a spin. Coupled with the conditional logic happening in item_fields from the inline plugin, this'll be a dream. I'm thinking:

item_fields:
    artist: %ifdef{artist_transl, $artist_transl, $artist}
    album: %ifdef{album_transl, $album_transl, $album}
    title: %ifdef{title_transl, $title_transl, $title}

While $albumartist_sort already comes in the language I'm after, English, with $artist being used for comp releases.

@semohr I don't have further changes if you agree with the latest additions.

In my head this is already approved! I'm waiting for some free time to have one closer look and merge this.

I haven't forgotten you, please be patient for a bit longer 🙏