I have an MP3 player that I use while I’m out. It uses a microSD card for storage. My personal media library, stored on my ⟐ NAS, is mostly FLAC, so when I want to transfer songs to the MP3 player, I need to transcode them to MP3.

The below script uses Python and mutagen to recursively transcode all FLAC files in a directory to MP3. It will confirm that the MP3 was correctly created, before deleting the original FLAC file.

import os
from pathlib import Path
import subprocess
from mutagen.flac import FLAC

def convert_flac_to_mp3(flac_path):
    try:
        # Get the output MP3 path
        mp3_path = str(flac_path).replace('.flac', '.mp3')
        
        # If MP3 already exists, skip
        if os.path.exists(mp3_path):
            print(f"MP3 already exists, skipping: {mp3_path}")
            return False

        # Read FLAC metadata
        flac_audio = FLAC(flac_path)
        
        # Construct ffmpeg command with overwrite prevention
        cmd = [
            'ffmpeg',
            '-i', str(flac_path),
            '-ab', '320k',  # 320kbps bitrate
            '-map_metadata', '0',  # Copy metadata
            '-id3v2_version', '3',  # Use ID3v2.3 tags
            '-n',  # Don't overwrite output files
            mp3_path
        ]
        
        # Execute conversion
        result = subprocess.run(cmd, capture_output=True, text=True)
        
        if result.returncode == 0:
            # Verify the MP3 file exists and has size > 0
            if os.path.exists(mp3_path) and os.path.getsize(mp3_path) > 0:
                print(f"Successfully converted: {flac_path}")
                # Delete original FLAC file
                # NOTE: Comment this out if you want to keep the original FLAC file
                os.remove(flac_path)
                print(f"Deleted original: {flac_path}")
                return True
            else:
                print(f"Conversion seemed successful but MP3 file is missing or empty: {mp3_path}")
                return False
        else:
            print(f"Error converting {flac_path}: {result.stderr}")
            return False
            
    except Exception as e:
        print(f"Error processing {flac_path}: {str(e)}")
        return False

def main():
    # Get the current directory
    directory = Path('.')
    
    # Find all FLAC files recursively
    flac_files = list(directory.rglob('*.flac'))
    
    if not flac_files:
        print("No FLAC files found.")
        return
    
    print(f"Found {len(flac_files)} FLAC files.")
    
    # Convert each FLAC file
    successful_conversions = 0
    for flac_file in flac_files:
        print(f"\nProcessing: {flac_file}")
        if convert_flac_to_mp3(flac_file):
            successful_conversions += 1
    
    print(f"\nConversion complete. Successfully converted {successful_conversions} of {len(flac_files)} files.")

if __name__ == '__main__':
    main()

It runs recursively in a directory, so I store it at the root of my microSD card. My process is:

1. Transfer FLAC files to the microSD card
2. Run the script

You could configure this to run on a schedule on your media drive, or tweak some of the code to not delete the FLAC file (search for the NOTE: line and comment out the line below it).

This works for me, and it saves a ton of space on my microSD card.