Sync FLAC music library to dumb MP3 players.

sync_music_to_mp3_player.rb

#!/usr/bin/env ruby

# This script syncs music to an MP3 player that only plays MP3s, according to
# the following rules:
#
# 1. Always copy files using a scheme that makes it easy to navigate based on folders:
#    $ARTIST/$ALBUM/$TRACK.mp3
# 2. If the destination track already exists as an MP3, do nothing.
# 3. If the source track is an MP3, copy it without any processing.
# 4. If the source track is a FLAC, transcode it to MP3 and copy the MP3.
#
# Adjust MUSIC_SOURCE and MUSIC_TARGET to meet your needs.
# 
# The "MP3 player" this script was intended for is actually a car head unit with
# a rudimentary folder browser.

require 'fileutils'

MUSIC_SOURCE = '/home/don/Music'
MUSIC_TARGET = '/run/media/don/USB DISK'

def sync_directory(artist, album = nil)
  puts "Artist: #{artist} | Album: #{album}"
  source_dir = build_path(MUSIC_SOURCE, '/', artist, album)
  target_dir = build_path(MUSIC_TARGET, ' - ', artist, album)

  songs_to_sync = Dir.children(source_dir).select do |child|
    is_music = false
    %w(flac mp3 m4a mp4 wma).each do |type|
      if child.end_with?(type)
        is_music = true
        break
      end
    end
    is_music
  end

  Dir.mkdir(target_dir) if !Dir.exist?(target_dir) && songs_to_sync.count > 0

  songs_to_sync.each do |song_to_sync|
    full_path = "#{source_dir}/#{song_to_sync}"
    sync_file(full_path, target_dir)
  end 
end

def sync_file(source_file, target_dir)
  if source_file.end_with?('mp3') # pass through
    return if File.exist?("#{target_dir}/#{File.basename(source_file)}")
    puts "Copying MP3: #{source_file}"
    FileUtils.cp(source_file, target_dir)
  else # transcode
    dest_file = "#{target_dir}/#{File.basename(source_file).gsub(File.extname(source_file), '.mp3')}"
    return if File.exist?(dest_file)
    puts "Transcoding: #{source_file}"
    `ffmpeg -i "#{source_file}" -b:a 320k "#{dest_file}"`
  end
end

def build_path(location, join, artist, album = nil)
  path = "#{location}/#{artist}"
  path += "#{join}#{album}" if album
  path
end

def subdirectories(path)
  Dir.children(path).select { |x| File.directory?("#{path}/#{x}") }
end

artists = subdirectories(MUSIC_SOURCE)
artists.each do |artist|
  sync_directory(artist)
  albums = subdirectories("#{MUSIC_SOURCE}/#{artist}")
  albums.each do |album|
    sync_directory(artist, album)
  end
end