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Design for Track Naming and Playlists

Original Design

This was pretty simple, based on the directory structure. Any .m3u playlist files were ignored. The playlist was built on the directories and filenames alone.

E.g.: for a base directory of home/rdawe/Music/cds and an album like:

$ find /home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose | sort -n
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/01.Stacked_Actors.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/02.BreakOut.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/03.Learn_to_Fly.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/04.Gimme_Stitches.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/05.Generator.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/06.Aurora.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/07.Live-In_Skin.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/08.Next_Year.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/09.Headwires.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/10.Aint_It_The_Life.flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/11.M.I.A..flac
/home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose/There_Is_Nothing_Left_To_Lose.m3u

The artist would be Foo_Fighters, the album would be There_Is_Nothing_Left_To_Lose, and the tracks would be 01.Stacked_Actors, etc. Given this, a playlist called Foo_Fighters :: There_Is_Nothing_Left_To_Lose would be constructed containing tracks 01.Stacked_Actors, etc.

This scheme works pretty well if you've structured your music library like this. This includes e.g.: an iTunes music library.

This scheme is also pretty simple to implement. There's no ambiguity about which playlist a track belongs to. If it's in a directory, it is in the playlist for that directory.

This scheme does not work so well for older music libraries like MP3s that may have been extracted with a flat structure. It also ignores any Vorbis or ID3 tags that the files may have. In many cases, it also does not work very for albums that have a different artist per track (e.g.: compilations or mixes).

Here are some examples from my MP3 library:

$ find /home/rdawe/Music/mp3/ -name 'good*' | sort -n | head -n 5
/home/rdawe/Music/mp3/good looking - logical progression (disc 01) (01) - ltj bukem - demon's theme.mp3
/home/rdawe/Music/mp3/good looking - logical progression (disc 01) (02) - chameleon - links.mp3
/home/rdawe/Music/mp3/good looking - logical progression (disc 01) (03) - ltj bukem - music.mp3
/home/rdawe/Music/mp3/good looking - logical progression (disc 01) (04) - pfm - one & only.mp3
/home/rdawe/Music/mp3/good looking - logical progression (disc 01) (05) - aquarius & tayla - bringing me down.mp3

$ find /home/rdawe/Music/mp3/ -name '*monkey kong*' | sort -n | head -n 5
/home/rdawe/Music/mp3/a - a vs. monkey kong (01) - for starters.mp3
/home/rdawe/Music/mp3/a - a vs. monkey kong (02) - monkey kong.mp3
/home/rdawe/Music/mp3/a - a vs. monkey kong (03) - a.mp3
/home/rdawe/Music/mp3/a - a vs. monkey kong (04) - old folks.mp3
/home/rdawe/Music/mp3/a - a vs. monkey kong (05) - hopper jonnus fang.mp3

New Design

Goals

  • Use Vorbis or ID3 tags (if present) to determine artist, album, etc.

  • Generate playlists based on tracks rather than file location, so that a directory full of music is split into multiple playlists.

  • Support determining artist, album, etc. from the filename using regular expressions, to match e.g.: my MP3 library.

  • If it's not possible to determine the artist, album, etc. using one method, fall back to the next one:

    • 1st: Tags
    • 2nd: Regular expression matches on filename.
    • 3rd: Directory + filename
    • Note: In some situations we may need to use tags for some fields, but directory when e.g.: album artist is missing (see sections below).

Virtual Playlist Locations

Each playlist has a location, which is a unique name for it. For playlists based on file location, this is the directory name, including the base directory for the storage instance. E.g.: /home/rdawe/Music/cds/Foo_Fighters/There_Is_Nothing_Left_To_Lose for the album "There Is Nothing Left To Lose" by the Foo Fighters.

What should we use for playlists based on tags or regex matches? Let's use fake URLs, e.g.: tags:/basepath/artist/album and regex:/basepath/artist/album. A more concrete example might look like regex:/home/rdawe/Music/mp3/artist/album.

Note that there is a playlist for each album by an artist. There is no support for a playlist covering a selection of songs, or multiple albums by an artist. Supporting that is not currently a goal.

The playlist ID is generated using the location. The playlist ID should be stable - i.e.: the same across restarts of minimediaserver.

Albums with Multiple Artists

Albums may have multiple artists. (I'm using the term "artist" here to cover author, composer, performer.) E.g.: an orchestra playing pieces by multiple composers. Or a compilation by multiple artists. In this case the album may have an overall "album artist" and then per-track artists. It is possible that the artist for the entire album is also the artist for one of the tracks.

For ID3 tags, there is a way to represent multiple artists, using TPE1, TPE2 and TPE3 comments. For Vorbis comments for Ogg and FLAC, there does not seem to be a standard tag. And in any case, the relevant tags may not be present - some heuristics may be required.

If it's possible to determine the "album artist" from the tags on a track, then the tracks can be grouped using (album artist, album).

For FLAC files with no album artist tags, the directory structure might indicate that it's a multi-author one (e.g.: "Various Artists/Album/track1.flac, etc.). In that case, we would want to use the directory name as the album artist, but could use the tags to determine the artist for the track. A reasonable heuristic here is that if directory name != artist from tags, then it's a multi-artist album. Artist names should be compared case-insensitively.

The files may have a CDDB tag, containing the unique ID for the album. This may be used as a reliable way of grouping tracks.

Grouping Tracks into a Playlist

Note: .m3u files are ignored by this design. Perhaps a future version of this design will consider using them. They are ignored in preference of using the audio files' tags as the source of truth.

To build a playlist, the media server needs to:

  • Find audio files ("tracks")
  • Examine each track to determine its artist, album, title, and album artist ("annotate" the track information)
  • Group tracks by (album artist, album) - one playlist per (album artist, album)

When tags are present, we should prefer grouping using the most unique fields available, in this order of preference:

  • tags:/basepath/albumId/album (e.g.: using CDDB database ID for the album)
  • tags:/basepath/albumArtist/album (e.g.: when it's a multi-artist album)
  • tags:/basepath/artist/album

TODO: Issues:

  • FLAC Vorbis tags seem to be missing overall artist tag (e.g.: "Various") - need some heuristics to figure out actual artist? Can use the CDDB tag to match albums too.
  • Probably need post-processing step for playlist to handle multi-artist album
  • Mermaid-format diagram of processing pipeline for DiskStorageService, since it's not straightforward anymore ;)