FLAC to ALAC Batch Converter

A fast, parallel batch converter that transforms FLAC files to ALAC (Apple Lossless) format while preserving all metadata and cover art. Built in Rust for maximum performance and reliability.

Features

• 🎵 Lossless conversion from FLAC to ALAC
• 📋 Complete metadata preservation (title, artist, album, genre, etc.)
• 🖼️ Cover art preservation
• ⚡ Parallel processing for fast batch conversion
• 🔍 Bit-perfect verification option (PCM comparison)
• 🖥️ Cross-platform (Windows, macOS, Linux)
• 💻 Dual interface: Command line + GUI
• 📁 Directory structure preservation
• 🛡️ Robust error handling

Installation

Prerequisites

• FFmpeg must be installed and available in your system PATH
  • Windows: Download from ffmpeg.org
  • macOS: brew install ffmpeg
  • Linux: sudo apt install ffmpeg (Ubuntu/Debian) or equivalent

From Source

git clone https://github.com/yourusername/flac2alac-batch.git
cd flac2alac-batch
cargo build --release

The binary will be available at target/release/flac2alac-batch (Linux/macOS) or target\release\flac2alac-batch.exe (Windows).

Usage

GUI Mode (Recommended)

Launch the graphical interface:

# Linux/macOS
./target/release/flac2alac-batch --gui

# Windows
target\release\flac2alac-batch.exe --gui

The GUI provides:

• Folder browsers for input/output selection
• Progress tracking with real-time updates
• Error reporting with detailed messages
• All conversion options in an intuitive interface

Command Line Mode

Basic usage:

# Convert single file
flac2alac-batch --input song.flac

# Convert entire directory
flac2alac-batch --input /path/to/flac/files

# Specify output directory
flac2alac-batch --input /music/flac --output /music/alac

Advanced options:

# Use 8 parallel jobs for faster conversion
flac2alac-batch --input /music --jobs 8

# Verify bit-perfect conversion (slower but ensures quality)
flac2alac-batch --input /music --verify

# Dry run (see what would be converted without doing it)
flac2alac-batch --input /music --dry-run

# Handle existing files
flac2alac-batch --input /music --overwrite replace  # replace existing
flac2alac-batch --input /music --overwrite skip     # skip existing
flac2alac-batch --input /music --overwrite prompt   # ask for each file

Full command reference:

Options:
  -i, --input <PATH>         FLAC file or directory containing FLAC files
  -o, --output <DIR>         Output directory (preserves structure, defaults to source directory)
  -j, --jobs <N>             Number of parallel conversion jobs
      --verify               Enable bit-perfect verification (PCM hash comparison)
      --overwrite <MODE>     How to handle existing files [default: skip] [possible values: skip, prompt, replace]
      --dry-run              Simulation mode: show what would be converted without doing it
      --gui                  Launch graphical user interface
  -h, --help                 Print help
  -V, --version              Print version

How It Works

Conversion Process

1. File Discovery: Recursively scans input directory for .flac files
2. Parallel Processing: Uses Rayon for CPU-efficient parallel conversion
3. FFmpeg Integration: Leverages FFmpeg for reliable audio conversion
4. Metadata Mapping: Explicitly maps FLAC Vorbis Comments to iTunes-compatible MP4 atoms
5. Quality Verification: Optionally compares PCM data to ensure bit-perfect conversion

Technical Details

Metadata Preservation:

• Maps FLAC Vorbis Comments to MP4/iTunes tags
• Preserves cover art as attached pictures
• Maintains all standard fields (title, artist, album, date, genre, track, album_artist)
• Custom fields are preserved when possible

Audio Quality:

• Pure lossless conversion (FLAC → PCM → ALAC)
• No resampling or quality loss
• Optional bit-perfect verification via SHA256 hash comparison
• Preserves original bit depth and sample rate

Performance:

• Parallel processing using all available CPU cores
• Efficient memory usage with streaming conversion
• Progress tracking for long-running batch jobs

FFmpeg Command Used

The tool uses this optimized FFmpeg command:

ffmpeg -i input.flac \
  -map 0:a:0 -map 0:v? \
  -c:a alac -c:v copy \
  -disposition:v attached_pic \
  -map_metadata 0 \
  -map_metadata:s:v:0 0:s:v:0 \
  output.m4a

Examples

Family Photo Organization

# Convert your entire music library
flac2alac-batch --input ~/Music/FLAC --output ~/Music/ALAC --jobs 8

# Verify quality for archival purposes
flac2alac-batch --input ~/Music/FLAC --verify --jobs 4

Single Album

# Convert specific album
flac2alac-batch --input "~/Music/Artist - Album (FLAC)"

# Preview what would be converted
flac2alac-batch --input "~/Music/Artist - Album (FLAC)" --dry-run

Troubleshooting

Common Issues

"FFmpeg not found":

• Ensure FFmpeg is installed and in your system PATH
• Test with ffmpeg -version in terminal

"No FLAC files found":

• Check that input path contains .flac files
• Ensure you have read permissions for the directory

Metadata missing in iTunes:

• This is usually resolved automatically with the current version
• Try re-importing files into iTunes after conversion

Permission errors:

• Ensure write permissions for output directory
• On Windows, try running as administrator if needed

Performance Tips

• Use --jobs parameter to match your CPU core count
• Place input/output on fast storage (SSD) for better performance
• For large libraries, consider converting in batches

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• Built with Rust for performance and safety
• Uses FFmpeg for audio conversion
• GUI powered by egui
• Parallel processing via Rayon