redoflacs

redoflacs is a parallel BASH command-line tool for managing a collection of
FLAC audio files. It can re-compress FLACs to maximize compression, verify and
their integrity, and organize or clean up metadata (tags and embedded artwork)
in bulk. By utilizing multi-core processing, redoflacs can perform these
operations quickly on large libraries of music.

Features

• Multi-core FLAC compression & verification – Re-encode FLAC files to the
  highest compression level (default level 8) while verifying each file's
  integrity. Ensures all files are compressed uniformly and correctly.

• Error checking (testing) – Scan FLAC files for any errors or corruption
  without altering them, logging any problematic files for review.

• MD5 checksum validation – Check the embedded MD5 signature of each FLAC
  file to identify files missing a checksum. This helps detect files that may
  need re-encoding to embed a proper MD5.

• Metadata pruning – Remove unnecessary metadata blocks from FLAC files
  (such as padding, seek tables, and embedded album art) to reduce file size.
  Only essential information (audio stream info and tags) is kept.

• Retagging – Clean up FLAC tags by removing all tags and reapplying only a
  defined set of essential tags. This ensures consistent, well-formed tags across
  your library (and trims any extraneous whitespace in tag values). Missing or
  empty required tags are reported for user review before any retagging occurs.

• ReplayGain calculation – Calculate and embed ReplayGain volume
  normalization tags (track and album gain/peak) for all files using metaflac.
  This allows consistent playback volume across tracks and albums. (Requires that
  each album’s tracks reside in separate directories for accurate album gain
  calculation.)

• Authenticity analysis – Use auCDtect or Lossless Audio Checker (LAC)
  tool to analyze audio data and detect files that might not be true lossless
  sources (e.g. upconverted from MP3). Suspect files are logged for attention.
  An extended mode can also generate spectral spectrogram images (requires
  SoX) for each suspect file to assist in manual inspection.

• Album art extraction – Extract all embedded cover images from FLAC files
  to external image files. This is useful for backing up album art before using
  the metadata pruning operation (which by default removes embedded art).
  Extracted images are saved to a folder (configurable) alongside each FLAC file.

Requirements

• Operating System: Unix-like environment (Linux/BSD; macOS should work
  with a newer Bash).
• Bash 4.0 or higher.
• FLAC: The FLAC tools package (includes flac
  and metaflac).
• Optional:
  • SoX (with PNG support) – only needed for generating spectrogram images.
  • auCDtect – only needed for authenticity check operations.
  • LAC – only needed for authenticity check operations.

Ensure the required programs are installed and in your $PATH before using
redoflacs. Optional tools can be installed to enable those specific features
(redoflacs will notify you if an optional tool is required but not found).

Installation

1. Download the script: You can get redoflacs by cloning the
   GitHub repository or downloading the
   latest release. The main script file is redoflacs (a single Bash script).

2. Install the script: Place the redoflacs script somewhere in your
   $PATH (for example, /usr/local/bin/) and ensure it is executable. For
   example:

   $ cp redoflacs /usr/local/bin/redoflacs
   $ chmod +x /usr/local/bin/redoflacs

3. Configuration (optional): On first run, redoflacs will create a
   configuration file at ~/.config/redoflacs/config with default settings. You
   can manually generate or reset this file by running redoflacs -o. Review this
   config file to adjust settings such as compression level, which tags to
   preserve during retagging, whether to remove album artwork during pruning, and
   where to save extracted artwork.

4. Verify installation: Run redoflacs -h to display the help text and
   verify that the script is working.

Usage

redoflacs [operations] [options] [target]

Common Operations

• Compress & Verify

  $ redoflacs -c ~/Music

  Re-encode every FLAC under ~/Music to compression level defined, verifying
  each file’s integrity. Adds a COMPRESSION tag to each file on success.

• Prune metadata from FLAC files

  $ redoflacs -p ~/Music

  Removes all non-essential metadata (including album art) from the FLAC files.

• Apply ReplayGain to an album

  $ redoflacs -g ~/Music/Artist/Album

  Calculates track and album ReplayGain for all FLACs in an album directory and
  adds the appropriate tags.

• Check FLAC authenticity and generate spectrograms

  $ redoflacs -A ~/Music

  Analyzes all FLACs in a directory with auCDtect to detect upscaled or
  lossy-sourced files.

• Combine multiple operations in one go

  $ redoflacs -c -p ~/Music

  Compress and prune metadata in a single command.

• Use compression jobs and threads

  $ redoflacs -J8 -T2 -C ~/Music

  Forcefully compress using 2 threads per job and 8 jobs.

Project Status and Contribution

redoflacs is an open-source project released under the MIT License.
Contributions such as bug fixes or improvements are welcome – feel free to fork
the repository and open a pull request on GitHub.

If you encounter any issues or have questions, please refer to the built-in
help (redoflacs -h) or the provided man page distributed with this program.