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bmux converts and compresses images, and tags local audio files for Spotify’s Local Files feature, without uploading them anywhere. The browser app does the work in your own tab; the CLI does the same jobs from a script, with no server involved for either — audio tagging’s only exception is the optional, opt-in MusicBrainz lookup in batch.
The CLI uses sharp, so unlike the browser it can write every supported format and can keep EXIF metadata when you ask it to.

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Quickstart

1

Install

See Installation for pnpm, yarn, and building from source.
2

Convert something

3

Check what you got

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Images

convert

Turn specific files into another format, with control over quality and size.

optimize

Run a whole directory through a preset without picking settings yourself.

inspect

Report what a file actually is, read from its contents rather than its name.

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Audio

Tag local mp3/flac/m4a files so Spotify’s Local Files feature shows their title, artist, album, and cover art correctly — the same feature lives in the browser app as the Spotify Tracks tab.

tag

Write specific fields — title, artist, album, track, year, cover art — on one file.

batch

Apply the same artist/album/year/cover to every file in a directory at once.

cover

Extract or replace embedded cover art on its own.

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Things that hold true everywhere

  • Originals are never overwritten. Colliding output names get a numeric suffix unless you choose otherwise with --collision.
  • Metadata is stripped by default. EXIF/XMP is removed unless you pass --preserve-metadata. Photos are still auto-rotated upright first.
  • A failed file doesn’t stop the rest. The batch finishes, the failures are listed, and the exit code is non-zero.
  • Nothing is uploaded. There is no server and no account. --dry-run will show you exactly what would be written before anything is.

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Colour output

Colour is used for status only — green for a saving, amber for a file that grew, red for a failure. It turns itself off when output isn’t a terminal, and it honours NO_COLOR: