Automatic singleton detection

[mried]

It would be great if beets is able to decide if a particular file should be imported as part of an album or a singleton. These need comes from my personal music library:
I've got a folder for each artist. Below the artist folder follow folders for each album of the artist as well as single files which do not belong to an album.
Example find-like output

> find /music
/music/artist1
/music/artist1/album1
/music/artist1/album1/01 - album_track.mp3
/music/artist1/album1/02 - album_track.mp3
/music/artist1/singleton_track_01.mp3

Using beet import /music will create two albums: One for album1 and one more or less random for the singleton. That's definitely not what I want 😉. The singletons can be identifies using the file name (they don't start with two or more digits followed by -).
To solve this, I see the following solutions:

1. Move all singletons away before starting the import; import everything else using beet import; move the files back; import every singleton file explicitly using beet import -s.
2. Implement a filter which filters out the file which should not be imported. The filter could use different configurations for the import of singletons and albums. So I could just write beet import /music; beet import -s /music.
3. Implement something that is able to decide how a file should be imported. Something like beet import --auto-singleton /music
   The first solution works right now but is a bad way 'cause it's very slow and not the way it should be done. The second one is the most flexible one whereas the third does not require two beet runs.

I'm willing to do all the implementation but we should decide how to do it first 😉

Suggestions are welcome!

[sampsyo]

Interesting request—the feature sounds useful, but also difficult to accomplish in a way that will make everyone happy (i.e., that filename pattern is idiosyncratic, and it seems sort of fiddly to have people writing regular expressions to classify this). One possibly-general filter would be to use singleton mode for folders containing only a single track, but that's not really perfect either.

Currently, you have one other option: the "as Tracks" choice in the importer UI. That switches to singleton mode for a specific "album" under consideration.

[mried]

Sure, there is the "as Tracks" when using the UI. But I want to run the import unattended (using "as-is" as default choice). So that won't work for me.

I also don't think that there is a generic way to implement this request since every music library might be set up differently. Maybe we should not implement this feature but a way to create different filters (my second solution).
To get this working, I found three ways:

1. The file-filter plugin hook I once implemented added a new plugin hook.
2. Add a new event import_task_created which is fired after the creation of the task. A plugin might change the task at this time.
3. Add a new way for plugins to insert pipeline stages. Right now, all plugin provided pipeline stages are added to the end of the pipeline. If there is a way to add stages after the first stage (or any other place) a filter stage could be added by a plugin.

[sampsyo]

Yes, indeed—I like your import_task_created event idea, which would also be useful for your other feature idea. Nice!

[mried]

I started to work on this issue again (see PR #1292).
Since it is hard to find a universal way to determine which files should be considered as singletons, I've got two suggestions:

1. Create an autosingletonbase "plugin" which can be used as a base class for individual implementations. When deriving this class, one has to override only one method like is_singleton which decides if a given task should be converted to singleton import tasks.
2. Try to find a set of rules which can be enabled/configured/mixed so they fit the individual situation. This might be very difficult to achieve.

I tend to the first idea.

[sampsyo]

I would love to avoid requiring people to create their own plugins as part of documented standard procedure. We could just suggest, as usual, that people with advanced needs like this create their own plugins from scratch, perhaps using example code we provide, but I'm not sure how I feel about shipping a sanctioned "base plugin" and telling people to modify it. Tricky situation!

[mried]

OK, I basically agree. So we won't implement the first idea. What about the second? Are we able to create a plugin which is generic enough to fit most use cases?

Here are the rules of my own plugin doing the singleton detection within my music library:

• If the containing folder is called misc, it's a singleton.
• If there is a directory inside the directory of the file, it's a singleton.
• If the filename does not start with at least two digits followed by -, it's a singleton.
• The rest is considered to be an album.

I could of course improve my plugin so the tests can be turned on and off and configured. But I'm not sure if this is a good idea since the configuration might soon get horrifically difficult.

[sampsyo]

Interesting. I note that most of these could be implemented by a regular expression on the path (i.e., they could mirror or be part of the filefilter plugin) except for the second criterion. Beyond that, I don't know what the best course of action is.

[justdan96]

Does anyone have a way to do this? All my singletons have an album field of "None" but I still have to manually specify to import them as a track during the import stage. Can it be easily automated?

[sampsyo]

Perhaps a good solution for you, @justdan96, would be to manually change those tracks to singletons using beet modify with the query album:None, sort of as suggested in #2747 (comment)?

[justdan96]

I'm importing a large music library all at once, I'd prefer to filter it at the import stage.