Sometimes audio files are accompanied by additional files that should keep the same name as the audio file they belong to, just with different file extension. Examples include:

• WavPack correction files .wvc (already handled in https://github.com/metabrainz/picard/blob/master/picard/formats/apev2.py)
• Ableton files .asd (see https://community.metabrainz.org/t/-/586506)
• Karaoke CDG files .cdg (https://community.mp3tag.de/t/cdg-files/6087)

There should be a UI where the user can define additional file extensions that are considered companion files to audio files. Whenever the audio files gets move and renamed the companion files should be as well.

It should also be possible to limit the companion files to specific formats, e.g. .wvc only makes sense for WavPack files.

There seem to be two cases to consider:

• The filename minus extension of the audio and companion are the same e.g. MySong.wv + MySong.wvc; or MySong.mp3 + MySong.cdg
• The companion file name is the same as the full audio file name plus an added extension. E.g. this seems to be the case for Ableton files (MySong.mp3 + MySong.mp3.asd)

Multiple companion files per audio file are possible.