14 KiB
Multi-artist support for non-MusicBrainz-tagged content
Terminology
The following terminology is used throughout this spec:
- Join phrase
- The token used to split a list of artists and represent their role in content
- Release
- An album or single. In Funkwhale a release is represented by the
Album
model - Recording
- A single track as part of an album or single. In Funkwhale, a recording is represented by the
Track
model
Proposed solution
To support multi-artist content, a new ArtistCredit
model should be added to house contributing artist information, including links to Artist
models and details about credited names and join phrases. The ArtistCredit
model should link to Album
and Track
entries using a ForeignKey
relationship to allow multiple artist_credit
entries on each Album
and Track
. The existing artist
field in Album
and Track
models is deprecated in favor of the new artist_credit
field.
To account for content tagged in tagged in systems other than MusicBrainz, a parse_credit
strategy should be used to parse artist credit from a file's metadata using join phrase parsing.
Feature behavior
The workflow for ArtistCredit
population goes as follows:
flowchart TD
upload([The user uploads content to Funkwhale])
upload --> read(Funkwhale reads the file tags of each release/recording)
read --> mb-tagged{Does the content have a MusicBrainz ID?}
mb-tagged -->|no| parse(Funkwhale parses the artists tag\nand splits the artist at any tokens\n in the join phrase list)
parse --> artist(Funkwhale creates Artist entries for any\nartists that aren't present in the database)
artist --> model(Funkwhale stores the <code>artist_credit</code> information\nfor each release/recording)
model --> display([Funkwhale displays the credit for each release/recording\nin the web app/API representation])
Backend
The backend is responsible for
- Tokenizing artist tags in the file's metadata and creating
Artist
entries for new artists - Creating
ArtistCredit
entries for each unique combination ofartist_id
,credit
, andjoinphrase
- Adding the
ArtistCredit
links toTrack
andAlbum
entries
The artist_credit
entries must be linked sequentially to preserve ordering. For each entry, Funkwhale should query for an existing ArtistCredit
entry and return it if found, or create a new one and return the new entry. This ensures that artist credit information is presented in the same order as in the tags.
Data model
A new ArtistCredit
model needs to hold the contributing artist information. This model contains the following fields:
- The Funkwhale
artist_id
of the artist associated with the release or recording - The
credit
representing the credited name of the artist as given for the release or recording - The
joinphrase
associated with the artist (for example:" feat. "
," & "
)
classDiagram
direction LR
class Album {
String title
ArtistCredit artist_credit
Date release_date
String release_group_id
Attachment attachment_cover
String type
Actor attributed_to
TaggedItem tagged_items
Fetch fetches
Content description
List api_includes
String api
String federation_namespace
MusicBrainz musicbrainz_model
String musicbrainz_mapping
}
class Track {
UUID mbid
String title
ArtistCredit artist_credit
Integer disc_number
Integer position
Album album
License license
Actor attributed_to
String copyright
Attachment attachment_cover
Integer downloads_count
String federation_namespace
String musicbrainz_model
String api
List api_includes
MusicBrainz musicbrainz_mapping
String import_hooks
QuerySet objects
Fetch fetches
}
class Artist {
String name
String federation_namespace
String musicbrainz_model
Object musicbrainz_mapping
Actor attributed_to
TaggedItem tagged_items
Fetch fetches
Content description
Attachment attachment_cover
String content_category
Date modification_date
String api
QuerySet objects
}
class ArtistCredit {
Artist artist_id
String credit
String joinphrase
}
Track "1" --> Album : album
Track "1..*" --> ArtistCredit : artist_credit
Album "1..*" --> ArtistCredit : artist_credit
ArtistCredit "1" --> Artist : Artist
Workflow
On the backend, the workflow for fetching ArtistCredit
information is as follows:
sequenceDiagram
ArtistCredit ->> parse_credit: Parse credit from tags
parse_credit -->> ArtistCredit: Return credit information
Funkwhale should provide the following to enable artist parsing in non-MusicBrainz-tagged content:
- A sensible list of default join phrases that are commonly found in artist tags
- A setting to enable admins to override or add to the list of join phrases
Funkwhale should tokenize the ALBUMARTIST
and ARTIST
fields using a list of join phrases. For each token in the list, Funkwhale should do the following:
- Store content split at the join phrase token as the
credit
- Search for any artist with the same name as the
credit
and store the id as theartist_id
- If no existing artist is found, create a new artist and return the ID as
artist_id
- If no existing artist is found, create a new artist and return the ID as
- Store the join phrase token that it split at as the
joinphrase
- Create an
ArtistCredit
object for each unique combination ofartist_id
,credit
, andjoinphrase
- If a matching
ArtistCredit
entry is found, Funkwhale should link to this
sequenceDiagram
Upload ->> parse_content: Read file metadata
loop For each artist name
parse_content ->> Artist: Search Artist entries
Artist -->> parse_content: Return entry (if exists)
parse_content ->> Artist: Create Artist entry (if none found)
end
loop For each unique artist credit combination
parse_content ->> ArtistCredit: Search ArtistCredit entries
ArtistCredit -->> parse_content: Return entry (if exists)
parse_content ->> ArtistCredit: Create ArtistCredit entry (if none found)
parse_content ->> Track: Create Track with artist_credit entries
parse_content ->> Album: Create Album with artist_credit entries
end
Funkwhale should do the following automatically:
- Trim whitespace from the artist
credit
- Preserve whitespace around both sides of the
joinphrase
for readability - Use an empty string (
""
) as thejoinphrase
for the last entry in the list
For example, given a list of join phrases like this:
$
,|
,&
,/
,feat.
And the following tags:
Tag | Values |
---|---|
ALBUMARTIST | Tommy J. & Bobby Forth |
ARTIST | Tommy J. feat. Robin Devil, Jerry Sabbath & Sammy Burns |
Funkwhale would create the following ArtistCredit
entries for the Album
:
id | artist_id | credit | joinphrase |
---|---|---|---|
1 | 1 | Tommy J. | & |
2 | 2 | Bobby Forth |
And the following for the Track
:
id | artist_id | credit | joinphrase |
---|---|---|---|
3 | 1 | Tommy J. | " feat. " |
4 | 3 | Robin Devil | ", " |
5 | 4 | Jerry Sabbath | " & " |
6 | 5 | Sammy Burns | "" |
API behavior
The Funkwhale API needs to return artist credit information in a way that is easily consumed by a client.
Endpoints should include a credited_artist
filter that allows a client to return results for which artists are credited. This filter should take a list of IDs.
To return any albums where the artist is listed in the artist_credit
field, you can filter by the artist_id
field using the credited_artist
filter:
https://open.audio/api/v2/albums?credited_artist=6451,6452
The credit
field of the artist_credit
object must also be searchable using a standard query:
https://tanukitunes.com/api/v2/albums?q=jonathan+coulton
Migration
To ensure all content has artist_credit
information, an initial migration should copy the current artist information into an ArtistCredit
object for each Album and Track with the following mapping:
artist_id
= Artistid
credit
= Artistname
joinphrase
=""
Each album/track must have at least one artist_credit
entry listed against it.
Frontend
To prevent issues with tagging, the user should be presented a summary of artist credits that are separated using the parse_credit
strategy.
Once the upload has been processed by the server, the user should be shown a summary of the uploaded content with artists listed against each recording and release. The user should then be able to amend these results and send a request to update the values. Upon receiving a new value, the server should perform the same deduplication it performs during a new upload.
- The user uploads new content to Funkwhale
- Funkwhale parses the artist credits and saves the new credit objects in case the upload is interrupted
- Funkwhale displays a summary of the changes
- If the results are correct, the user accepts the changes and finishes the upload
- If the results are incorrect, the user modifies the artist credits and submits the changes
flowchart TD
upload([The user uploads content to Funkwhale])
upload --> read(Funkwhale reads the file tags of each release/recording)
read --> parse(Funkwhale parses the artists tag\nand splits the artist at any tokens\n in the join phrase list)
parse --> artist(Funkwhale creates Artist entries for any\nartists that aren't present in the database)
artist --> model(Funkwhale stores the artist_credit information\nfor each release/recording)
model --> verify(Funkwhale displays the results to the user)
verify --> correct{Are the artist tags correct?}
correct -->|no| tweak(The user corrects the details and\nsubmits the new information to Funkwhale)
tweak & correct -->|yes| finish(The user finishes the upload process)
Representation in releases and tracks
The frontend should use the artist_credit
field to populate artist links on releases and tracks. Credited names and join phrases must be preserved to line up with the artists' intent.
The frontend should format the results as follows for each artist:
<span>
<a href="{funkwhale_url}/library/artists/{artist_id}">{credit}</a>{joinphrase}
</span>
For example, given the following artist_credit
response:
[
{
"artist_id": 25,
"credit": "Jonathan Coulton",
"joinphrase": " & "
},
{
"artist_id": 395,
"credit": "John Roderick",
"joinphrase": ""
}
]
The frontend would render the following:
<span>
<a href="https://open.audio/library/artists/25">Jonathan Coulton</a> &
<a href="https://open.audio/library/artists/395">John Roderick</a>
</span>
"Also appears in" section
To keep artist discographies properly catalogued, only albums attributed to the artist, not albums with tracks featuring the artist, should appear in the "Albums by" section of the artist page.
Releases to which the artist has contributed should be separated into a new section labeled "Also appears in". This ensures that it is easy to discover content to which an artist has contributed while also prioritizing their own content on the artist page.
"Compilations" page
The "Various Artists" artist is a special artist used in MusicBrainz to catalogue compilation content not attributed primarily to a specific artist or artists. This artist is widely used in Funkwhale as the Album Artist tag for compilation content. To preserve this content and make compilation content easier to find, we should create a special "Compilations" page to house compilation content.
Documentation
The following needs to be documented:
- The artist splitting mechanism. Meaningful examples should be provided to help users tag their content
- The environment setting to override the join phrase list
- Any tasks or script functions which are created to automate the update of historical content
Availability
- Admin panel
- App frontend
- CLI
Responsible parties
- The backend developers in the Development group are responsible for:
- Creating the new
ArtistCredit
model - Updating the
Album
andTrack
models to link toArtistCredit
entries - Creating the strategies for populating
ArtistCredit
during the upload process - Updating the API/creating new endpoints
- Creating the database migration to add the new field and that artist information is copied over
- Creating the new
- The frontend developers in the Development group are responsible for:
- Updating the artist representations in the Album and Track pages to use the new
artist_credit
field in the API response - Creating the new "Also appears in" section for the artist discography pages
- Creating a workflow to enable users to verify uploaded data and fix any broken artist credits
- Updating the artist representations in the Album and Track pages to use the new
- The Design group is responsible for:
- Providing designs for how multi-artist content should be rendered responsively
- Providing designs for the new "Compilations" page
- Providing designs for the updated Artist page
- The Documentation group is responsible for:
- Documenting the new feature behavior
- Documenting the new environment settings
- Providing docstrings for API development
Open questions
- What should be used as the default join words list?
- To maintain compatibility with API v1, should we continue to populate the
artist
tag onTrack
andAlbum
entries with the first credited artist?
Minimum viable product
The MVP for this product is an implementation of the backend behavior. It should:
- Set up the new models
- Create the database migration
- Implement the token splitting and data fetching for new files
Next steps
- Create a
manage.py
script that enables admins to update entries in the database - Create a task that updates files imported in-place