diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 9220c02..d7dc40f 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -1,76 +1,52 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2020-12-30 04:27:41 UTC using RuboCop version 1.7.0.
+# on 2021-01-03 08:54:57 UTC using RuboCop version 1.7.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
 
-# Offense count: 2
+# Offense count: 1
 # Configuration parameters: AllowSafeAssignment.
 Lint/AssignmentInCondition:
   Exclude:
-    - 'lib/audioinfo.rb'
     - 'lib/audioinfo/album.rb'
 
-# Offense count: 1
-Lint/RescueException:
-  Exclude:
-    - 'lib/audioinfo.rb'
-
-# Offense count: 1
-Lint/ShadowedException:
-  Exclude:
-    - 'lib/audioinfo.rb'
-
-# Offense count: 2
-Lint/ShadowingOuterLocalVariable:
-  Exclude:
-    - 'lib/audioinfo.rb'
-
-# Offense count: 1
-# Configuration parameters: AllowComments.
-Lint/SuppressedException:
-  Exclude:
-    - 'lib/audioinfo.rb'
-
-# Offense count: 5
+# Offense count: 3
 Lint/UselessAssignment:
   Exclude:
-    - 'lib/audioinfo.rb'
     - 'lib/audioinfo/mpcinfo.rb'
 
-# Offense count: 7
+# Offense count: 10
 # Configuration parameters: IgnoredMethods, CountRepeatedAttributes.
 Metrics/AbcSize:
-  Max: 177
+  Max: 166
 
 # Offense count: 2
 # Configuration parameters: CountComments, CountAsOne.
 Metrics/ClassLength:
-  Max: 322
+  Max: 128
 
 # Offense count: 4
 # Configuration parameters: IgnoredMethods.
 Metrics/CyclomaticComplexity:
-  Max: 29
+  Max: 14
 
-# Offense count: 8
+# Offense count: 16
 # Configuration parameters: CountComments, CountAsOne, ExcludedMethods, IgnoredMethods.
 Metrics/MethodLength:
-  Max: 117
+  Max: 70
 
-# Offense count: 4
+# Offense count: 3
 # Configuration parameters: IgnoredMethods.
 Metrics/PerceivedComplexity:
-  Max: 24
+  Max: 16
 
-# Offense count: 6
+# Offense count: 5
 # Configuration parameters: MinNameLength, AllowNamesEndingInNumbers, AllowedNames, ForbiddenNames.
 # AllowedNames: at, by, db, id, in, io, ip, of, on, os, pp, to
 Naming/MethodParameterName:
   Exclude:
-    - 'lib/audioinfo.rb'
     - 'lib/audioinfo/mpcinfo.rb'
 
 # Offense count: 1
@@ -84,15 +60,24 @@ Naming/PredicateName:
     - 'spec/**/*'
     - 'lib/audioinfo.rb'
 
-# Offense count: 4
+# Offense count: 13
 Style/Documentation:
   Exclude:
     - 'spec/**/*'
     - 'test/**/*'
     - 'lib/audioinfo.rb'
     - 'lib/audioinfo/album.rb'
+    - 'lib/audioinfo/ape.rb'
+    - 'lib/audioinfo/audio_file.rb'
     - 'lib/audioinfo/case_insensitive_hash.rb'
+    - 'lib/audioinfo/flac.rb'
+    - 'lib/audioinfo/mp3.rb'
+    - 'lib/audioinfo/mp4.rb'
+    - 'lib/audioinfo/mpc.rb'
     - 'lib/audioinfo/mpcinfo.rb'
+    - 'lib/audioinfo/ogg.rb'
+    - 'lib/audioinfo/wav.rb'
+    - 'lib/audioinfo/wma.rb'
 
 # Offense count: 4
 # Configuration parameters: MaxUnannotatedPlaceholdersAllowed.
@@ -100,11 +85,10 @@ Style/Documentation:
 Style/FormatStringToken:
   EnforcedStyle: unannotated
 
-# Offense count: 8
+# Offense count: 9
 # Configuration parameters: MinBodyLength.
 Style/GuardClause:
   Exclude:
-    - 'lib/audioinfo.rb'
     - 'lib/audioinfo/album.rb'
     - 'lib/audioinfo/mpcinfo.rb'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index b01f39e..a889071 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -59,6 +59,7 @@ GEM
     wavefile (0.6.0)
 
 PLATFORMS
+  ruby
   universal-java-1.8
   x86_64-darwin-20
   x86_64-linux
diff --git a/lib/audioinfo.rb b/lib/audioinfo.rb
index 3604a8a..b00be56 100644
--- a/lib/audioinfo.rb
+++ b/lib/audioinfo.rb
@@ -2,38 +2,19 @@
 
 require 'stringio'
 
-require 'mp3info'
-require 'ogginfo'
-require 'wmainfo'
-require 'mp4info'
-require 'flacinfo'
-require 'apetag'
-require 'wavefile'
-
-$LOAD_PATH << __dir__
-
+require 'audioinfo/audio_file'
+require 'audioinfo/mp3'
 require 'audioinfo/mpcinfo'
-require 'audioinfo/case_insensitive_hash'
+require 'audioinfo/ogg'
 require 'audioinfo/version'
+require 'audioinfo/wma'
+require 'audioinfo/wav'
+require 'audioinfo/mp4'
+require 'audioinfo/flac'
 
 class AudioInfoError < StandardError; end
 
-class AudioInfo
-  MUSICBRAINZ_FIELDS = {
-    'trmid'         => 'TRM Id',
-    'artistid'      => 'Artist Id',
-    'albumid'       => 'Album Id',
-    'albumtype'	    => 'Album Type',
-    'albumstatus'   => 'Album Status',
-    'albumartistid' => 'Album Artist Id',
-    'sortname'      => 'Sort Name',
-    'trackid'       => 'Track Id'
-  }.freeze
-
-  SUPPORTED_EXTENSIONS = %w[mp3 ogg opus spx mpc wma mp4 aac m4a flac wav].freeze
-
-  attr_reader :path, :extension, :musicbrainz_infos, :tracknum, :bitrate, :vbr, :artist, :album, :title, :length, :date
-
+module AudioInfo
   # Part of testing API - you should not use this directly
   attr_reader :info
 
@@ -62,363 +43,29 @@ def self.is_audio_file?(path)
   end
 
   # open the file with path +fn+
-  def initialize(filename, extension = nil)
+  def self.new(filename, extension = nil)
     raise(AudioInfoError, 'path is nil') if filename.nil?
 
-    @path = filename
-    ext = File.extname(@path)
-    @extension = extension || (ext && ext[1..].downcase)
-    raise(AudioInfoError, 'cannot find extension') if @extension.empty?
-
-    @musicbrainz_infos = {}
-
-    begin
-      case @extension
-      when 'mp3'
-        @info = Mp3Info.new(filename)
-        default_tag_fill
-        # "TXXX"=>
-        # ["MusicBrainz TRM Id\000",
-        # "MusicBrainz Artist Id\000aba64937-3334-4c65-90a1-4e6b9d4d7ada",
-        # "MusicBrainz Album Id\000e1a223c1-cbc2-427f-a192-5d22fefd7c4c",
-        # "MusicBrainz Album Type\000album",
-        # "MusicBrainz Album Status\000official",
-        # "MusicBrainz Album Artist Id\000"]
-
-        if (arr = @info.tag2['TXXX']).is_a?(Array)
-          fields = MUSICBRAINZ_FIELDS.invert
-          arr.each do |val|
-            if val =~ /^MusicBrainz (.+)\000(.*)$/
-              short_name = fields[Regexp.last_match(1)]
-              @musicbrainz_infos[short_name] = Regexp.last_match(2).gsub("\xEF\xBB\xBF".force_encoding('UTF-8'), '')
-            end
-          end
-        end
-        @bitrate = @info.bitrate
-        i = @info.tag.tracknum
-        @tracknum = (i.is_a?(Array) ? i.last : i).to_i
-        @length = @info.length.to_i
-        @date = @info.tag['date']
-        @vbr = @info.vbr
-        @info.close
-
-      when 'ogg', 'opus', 'spx'
-        @info = OggInfo.new(filename)
-        default_fill_musicbrainz_fields
-        default_tag_fill
-        @bitrate = @info.bitrate / 1000
-        @tracknum = @info.tag.tracknumber.to_i
-        @length = @info.length.to_i
-        @date = @info.tag['date']
-        @vbr = true
-        @info.close
-
-      when 'mpc'
-        fill_ape_tag(filename)
-        mpc_info = MpcInfo.new(filename)
-        @bitrate = mpc_info.infos['bitrate'] / 1000
-        @length = mpc_info.infos['length']
+    ext = File.extname(filename)
 
-      when 'ape'
-        fill_ape_tag(filename)
+    extension ||= (ext && ext[1..].downcase)
 
-      when 'wma'
-        @info = WmaInfo.new(filename, encoding: 'utf-8')
-        @artist = @info.tags['Author']
-        @album = @info.tags['AlbumTitle']
-        @title = @info.tags['Title']
-        @tracknum = @info.tags['TrackNumber'].to_i
-        @date = @info.tags['Year']
-        @bitrate = @info.info['bitrate']
-        @length = @info.info['playtime_seconds']
-        MUSICBRAINZ_FIELDS.each do |key, original_key|
-          @musicbrainz_infos[key] =
-            @info.info["MusicBrainz/#{original_key.tr(' ', '')}"] ||
-            @info.info["MusicBrainz/#{original_key}"]
-        end
-
-      when 'mp4', 'aac', 'm4a'
-        @extension = 'mp4'
-        @info = MP4Info.open(filename)
-        @artist = @info.ART
-        @album = @info.ALB
-        @title = @info.NAM
-        @tracknum = (t = @info.TRKN) ? t.first : 0
-        @date = @info.DAY
-        @bitrate = @info.BITRATE
-        @length = @info.SECS
-        mapping = MUSICBRAINZ_FIELDS.invert
-
-        faad_info(filename).scan(/^MusicBrainz (.+): (.+)$/) do |match|
-          name, value = match
-          key = mapping[name]
-          next unless key
-
-          @musicbrainz_infos[key] = value.strip.gsub("\u0000", '')
-        end
-
-      when 'flac'
-        @info = FlacInfo.new(filename)
-        # Unfortunately, FlacInfo doesn't allow us to fiddle inside
-        # their class, so we have to brute force it. Any other
-        # solution (e.g. creating another abstraction or getting
-        # methods) lands up being more messy and brittle.
-        @info.instance_variable_set('@tags', CaseInsensitiveHash.new(@info.tags))
-
-        get_tag = proc do |name|
-          if t = @info.tags[name]
-            t.dup.force_encoding('utf-8')
-          end
-        end
-
-        @artist = get_tag.call('artist')
-        @album = get_tag.call('album')
-        @title = get_tag.call('title')
-        @tracknum = @info.tags['tracknumber'].to_i
-        @date = get_tag.call('date')
-        @bitrate = 0
-        @length = @info.streaminfo['total_samples'] / @info.streaminfo['samplerate'].to_f
-        @bitrate = File.size(filename).to_f * 8 / @length / 1024 if @length.positive?
-        @info.tags.each do |tagname, _tagvalue|
-          next unless tagname =~ /^musicbrainz_(.+)$/
-
-          @musicbrainz_infos[Regexp.last_match(1)] = get_tag.call(tagname)
-        end
-        @musicbrainz_infos['trmid'] = @info.tags['musicip_puid']
-      # default_fill_musicbrainz_fields
-
-      when 'wav'
-        @info = WaveFile::Reader.info(filename)
-        @length = @info.duration.hours * 3600 + @info.duration.minutes * 60 + @info.duration.seconds +
-                  @info.duration.milliseconds * 0.001
-        @bitrate = File.size(filename) * 8 / @length / 1024
+    raise(AudioInfoError, 'cannot find extension') if extension.empty?
 
+    klass =
+      case extension
+      when 'mp3' then Mp3
+      when 'ogg', 'opus', 'spx' then Ogg
+      when 'mpc' then Mpc
+      when 'ape' then Ape
+      when 'wma' then Wma
+      when 'mp4', 'aac', 'm4a' then Mp4
+      when 'flac' then Flac
+      when 'wav' then Wav
       else
         raise(AudioInfoError, "unsupported extension '.#{@extension}'")
       end
 
-      @tracknum = nil if @tracknum&.zero?
-
-      @musicbrainz_infos.delete_if { |_k, v| v.nil? }
-      @hash = { 'artist' => @artist,
-                'album' => @album,
-                'title' => @title,
-                'tracknum' => @tracknum,
-                'date' => @date,
-                'length' => @length,
-                'bitrate' => @bitrate }
-    rescue StandardError, Mp3InfoError, OggInfoError, ApeTagError => e
-      raise AudioInfoError, e.to_s, e.backtrace
-    end
-
-    @needs_commit = false
-  end
-
-  # set the title of the file
-  def title=(v)
-    if @title != v
-      @needs_commit = true
-      @title = v
-    end
-  end
-
-  # set the artist of the file
-  def artist=(v)
-    if @artist != v
-      @needs_commit = true
-      @artist = v
-    end
-  end
-
-  # set the album of the file
-  def album=(v)
-    if @album != v
-      @needs_commit = true
-      @album = v
-    end
-  end
-
-  # set the track number of the file
-  def tracknum=(v)
-    v = v.to_i
-    if @tracknum != v
-      @needs_commit = true
-      @tracknum = v
-    end
-  end
-
-  def picture=(filepath)
-    if @picture != filepath
-      @needs_commit = true
-      @picture = filepath
-    end
-  end
-
-  # hash-like access to tag
-  def [](key)
-    @hash[key]
-  end
-
-  # convert tags to hash
-  def to_h
-    @hash
-  end
-
-  # close the file and commits changes to disk
-  def close
-    if @needs_commit
-      case @info
-      when Mp3Info
-        Mp3Info.open(@path) do |info|
-          info.tag.artist = @artist
-          info.tag.title = @title
-          info.tag.album = @album
-          info.tag.tracknum = @tracknum
-          if @picture
-            info.tag2.remove_pictures
-            info.tag2.add_picture(File.binread(@picture))
-          end
-        end
-      when OggInfo
-        OggInfo.open(@path) do |ogg|
-          { 'artist' => @artist,
-            'album' => @album,
-            'title' => @title,
-            'tracknumber' => @tracknum }.each do |k, v|
-            ogg.tag[k] = v.to_s
-          end
-          ogg.picture = @picture if @picture
-        end
-
-      when ApeTag
-        ape = ApeTag.new(@path)
-        ape.update do |fields|
-          fields['Artist'] = @artist
-          fields['Album'] = @album
-          fields['Title'] = @title
-          fields['Track'] = @tracknum.to_s
-        end
-      else
-        have_metaflac = system('which metaflac > /dev/null')
-        have_ffmpeg = system('which ffmpeg > /dev/null')
-        if have_metaflac && @info.is_a?(FlacInfo)
-          tags = { 'ARTIST' => @artist,
-                   'ALBUM' => @album,
-                   'TITLE' => @title,
-                   'TRACKNUMBER' => @tracknum }.inject([]) do |tags, (key, value)|
-            tags + ['--set-tag', "#{key}=#{value}"]
-          end
-          tag_with_shell_command('metaflac', '--remove-all', :src)
-          tag_with_shell_command('metaflac', tags, :src)
-        elsif have_ffmpeg
-          tags = { 'artist' => @artist,
-                   'album' => @album,
-                   'title' => @title }.inject([]) do |tags, (key, value)|
-            tags + ['-metadata', "#{key}=#{value}"]
-          end
-          tag_with_shell_command('ffmpeg', '-y', '-i', :src, '-loglevel', 'quiet', tags, :dst)
-        else
-          raise(AudioInfoError, 'implement me')
-        end
-      end
-    end
-    @needs_commit
-  end
-  #    {"musicbrainz_albumstatus"=>"official",
-  #     "artist"=>"Jill Scott",
-  #     "replaygain_track_gain"=>"-3.29 dB",
-  #     "tracknumber"=>"1",
-  #     "title"=>"A long walk (A touch of Jazz Mix)..Jazzanova Love Beats...",
-  #     "musicbrainz_sortname"=>"Scott, Jill",
-  #     "musicbrainz_artistid"=>"b1fb6a18-1626-4011-80fb-eaf83dfebcb6",
-  #     "musicbrainz_albumid"=>"cb2ad8c7-4a02-4e46-ae9a-c7c2463c7235",
-  #     "replaygain_track_peak"=>"0.82040048",
-  #     "musicbrainz_albumtype"=>"compilation",
-  #     "album"=>"...Mixing (Jazzanova)",
-  #     "musicbrainz_trmid"=>"1ecec0a6-c7c3-4179-abea-ef12dabc7cbd",
-  #     "musicbrainz_trackid"=>"0a368e63-dddf-441f-849c-ca23f9cb2d49",
-  #     "musicbrainz_albumartistid"=>"89ad4ac3-39f7-470e-963a-56509c546377"}>
-
-  # check if the file is correctly tagged by MusicBrainz
-  def mb_tagged?
-    !@musicbrainz_infos.empty?
-  end
-
-  private
-
-  def sanitize(input)
-    s = input.is_a?(Array) ? input.first : input
-    s.delete("\000")
-  end
-
-  def default_fill_musicbrainz_fields(tags = @info.tag)
-    MUSICBRAINZ_FIELDS.each_key do |field|
-      val = tags["musicbrainz_#{field}"]
-      @musicbrainz_infos[field] = val if val
-    end
-  end
-
-  def default_tag_fill(tags = @info.tag)
-    %w[artist album title].each do |v|
-      instance_variable_set("@#{v}".to_sym, sanitize(tags[v] || ''))
-    end
-  end
-
-  def fill_ape_tag(filename)
-    @info = ApeTag.new(filename)
-    tags = @info.fields.each_with_object({}) do |(k, v), hash|
-      hash[k.downcase] = v ? v.first : nil
-    end
-    default_fill_musicbrainz_fields(tags)
-    default_tag_fill(tags)
-
-    @date = tags['year']
-    @tracknum = tags['track'].to_i
-  rescue ApeTagError
-  end
-
-  def faad_info(path)
-    require 'open3'
-
-    output = ''
-    status = nil
-
-    begin
-      Open3.popen3('faad', '-i', path) do |_stdin, _stdout, stderr, wait_thr|
-        output = stderr.read.chomp
-        status = wait_thr.value
-      end
-    rescue StandardError
-    end
-
-    status&.exitstatus&.zero? ? output : ''
-  end
-
-  def shell_escape(s)
-    "'#{s.gsub(/'/) { "'\\''" }}'"
-  end
-
-  def tag_with_shell_command(*command_arr)
-    expand_command = proc do |hash|
-      command_arr.collect do |token|
-        token.is_a?(Symbol) ? hash[token] : token
-      end.flatten
-    end
-
-    hash = { src: @path }
-    if command_arr.include?(:dst)
-      Tempfile.open(['ruby-audioinfo', ".#{@extension}"]) do |tf|
-        cmd = expand_command.call(hash.merge(dst: tf.path))
-        tf.close
-        if system(*cmd)
-          FileUtils.mv(tf.path, @path)
-        else
-          raise(AudioInfoError, "error while running #{command_arr[0]}")
-        end
-      end
-    else
-      cmd = expand_command.call(hash)
-      system(*cmd) || raise(AudioInfoError, "error while running #{command_arr[0]}")
-    end
+    klass.new(filename, extension)
   end
 end
diff --git a/lib/audioinfo/album.rb b/lib/audioinfo/album.rb
index e1cbbc6..cbd91e2 100644
--- a/lib/audioinfo/album.rb
+++ b/lib/audioinfo/album.rb
@@ -6,6 +6,8 @@ module AudioInfo
   class Album
     IMAGE_EXTENSIONS = %w[jpg jpeg gif png].freeze
 
+    SUPPORTED_EXTENSIONS = %w[mp3 ogg opus spx mpc wma mp4 aac m4a flac wav].freeze
+
     # a regexp to match the "multicd" suffix of a "multicd" string
     # example: "toto (disc 1)" will match ' (disc 1)'
     MULTICD_REGEXP = /\s*(\(|\[)?\s*(disc|cd):?-?\s*(\d+).*(\)|\])?\s*$/i.freeze
@@ -46,7 +48,7 @@ def initialize(path, fast_lookup = false)
       @path = path
       @multicd = false
       @basename = @path
-      exts = AudioInfo::SUPPORTED_EXTENSIONS.collect do |ext|
+      exts = SUPPORTED_EXTENSIONS.collect do |ext|
         ext.gsub(/[a-z]/) { |c| "[#{c.downcase}#{c.upcase}]" }
       end.join(',')
 
diff --git a/lib/audioinfo/ape.rb b/lib/audioinfo/ape.rb
new file mode 100644
index 0000000..0e903ef
--- /dev/null
+++ b/lib/audioinfo/ape.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require 'apetag'
+
+module AudioInfo
+  class Ape < AudioFile
+    def parse(filename)
+      @info = ApeTag.new(filename)
+
+      tags = @info.fields.each_with_object({}) do |(k, v), hash|
+        hash[k.downcase] = v ? v.first : nil
+      end
+
+      default_fill_musicbrainz_fields(tags)
+      default_tag_fill(tags)
+
+      @date = tags['year']
+      @tracknum = tags['track'].to_i
+    rescue ApeTagError => e
+      raise AudioInfoError, e.to_s, e.backtrace
+    end
+
+    def close
+      return unless @needs_commit
+
+      ape = ApeTag.new(@path)
+      ape.update do |fields|
+        fields['Artist'] = @artist
+        fields['Album'] = @album
+        fields['Title'] = @title
+        fields['Track'] = @tracknum.to_s
+      end
+
+      @needs_commit
+    end
+  end
+end
diff --git a/lib/audioinfo/audio_file.rb b/lib/audioinfo/audio_file.rb
new file mode 100644
index 0000000..f50bdc7
--- /dev/null
+++ b/lib/audioinfo/audio_file.rb
@@ -0,0 +1,158 @@
+# frozen_string_literal: true
+
+module AudioInfo
+  class AudioFile
+    MUSICBRAINZ_FIELDS = {
+      'trmid'         => 'TRM Id',
+      'artistid'      => 'Artist Id',
+      'albumid'       => 'Album Id',
+      'albumtype'	    => 'Album Type',
+      'albumstatus'   => 'Album Status',
+      'albumartistid' => 'Album Artist Id',
+      'sortname'      => 'Sort Name',
+      'trackid'       => 'Track Id'
+    }.freeze
+
+    attr_reader :path, :extension, :musicbrainz_infos, :tracknum, :bitrate, :vbr, :artist, :album, :title, :length,
+                :date
+
+    def initialize(filename, extension)
+      @path = filename
+      ext = File.extname(@path)
+      @extension = extension || (ext && ext[1..].downcase)
+      @musicbrainz_infos = {}
+      @tracknum = nil
+      @artist = nil
+      @album = nil
+      @title = nil
+      # @date = nil
+
+      parse(filename)
+
+      @tracknum = nil if @tracknum&.zero?
+      @needs_commit = false
+      @musicbrainz_infos.delete_if { |_k, v| v.nil? }
+
+      @hash = {
+        'artist'   => @artist,
+        'album'    => @album,
+        'title'    => @title,
+        'tracknum' => @tracknum,
+        'date'     => @date,
+        'length'   => @length,
+        'bitrate'  => @bitrate
+      }
+    end
+
+    def mb_tagged?
+      !@musicbrainz_infos.empty?
+    end
+
+    # convert tags to hash
+    def to_h
+      @hash
+    end
+
+    def title=(new_title)
+      return if @title == new_title
+
+      @needs_commit = true
+      @title = new_title
+    end
+
+    def artist=(new_artist)
+      return if @artist == new_artist
+
+      @needs_commit = true
+      @artist = new_artist
+    end
+
+    def album=(new_album)
+      return if @album == new_album
+
+      @needs_commit = true
+      @album = new_album
+    end
+
+    def tracknum=(tracknum_s)
+      new_tracknum = tracknum_s.to_i
+      return if @tracknum == new_tracknum
+
+      @needs_commit = true
+      @tracknum = new_tracknum
+    end
+
+    def picture=(filepath)
+      return if @picture == filepath
+
+      @needs_commit = true
+      @picture = filepath
+    end
+
+    # hash-like access to tag
+    def [](key)
+      @hash[key]
+    end
+
+    def close
+      return unless @needs_commit
+
+      have_ffmpeg = system('which ffmpeg > /dev/null')
+
+      raise(AudioInfoError, "ffmpeg is required to write this file type and wasn't found") unless have_ffmpeg
+
+      tags = { 'artist' => @artist,
+               'album' => @album,
+               'title' => @title }.inject([]) do |t, (key, value)|
+        t + ['-metadata', "#{key}=#{value}"]
+      end
+
+      tag_with_shell_command('ffmpeg', '-y', '-i', :src, '-loglevel', 'quiet', tags, :dst)
+
+      @needs_commit
+    end
+
+    protected
+
+    def default_tag_fill(tags = @info.tag)
+      %w[artist album title].each do |v|
+        instance_variable_set("@#{v}".to_sym, sanitize(tags[v] || ''))
+      end
+    end
+
+    def default_fill_musicbrainz_fields(tags = @info.tag)
+      MUSICBRAINZ_FIELDS.each_key do |field|
+        val = tags["musicbrainz_#{field}"]
+        @musicbrainz_infos[field] = val if val
+      end
+    end
+
+    def sanitize(input)
+      s = input.is_a?(Array) ? input.first : input
+      s.delete("\000")
+    end
+
+    def tag_with_shell_command(*command_arr)
+      expand_command = proc do |hash|
+        command_arr.collect do |token|
+          token.is_a?(Symbol) ? hash[token] : token
+        end.flatten
+      end
+
+      hash = { src: @path }
+      if command_arr.include?(:dst)
+        Tempfile.open(['ruby-audioinfo', ".#{@extension}"]) do |tf|
+          cmd = expand_command.call(hash.merge(dst: tf.path))
+          tf.close
+
+          raise(AudioInfoError, "error while running #{command_arr[0]}") unless system(*cmd)
+
+          FileUtils.mv(tf.path, @path)
+        end
+      else
+        cmd = expand_command.call(hash)
+        system(*cmd) || raise(AudioInfoError, "error while running #{command_arr[0]}")
+      end
+    end
+  end
+end
diff --git a/lib/audioinfo/case_insensitive_hash.rb b/lib/audioinfo/case_insensitive_hash.rb
index c5717ff..4bd495f 100644
--- a/lib/audioinfo/case_insensitive_hash.rb
+++ b/lib/audioinfo/case_insensitive_hash.rb
@@ -1,18 +1,20 @@
 # frozen_string_literal: true
 
-class CaseInsensitiveHash < Hash
-  def initialize(hash = {})
-    super
-    hash.each do |key, value|
-      self[key.downcase] = value
+module AudioInfo
+  class CaseInsensitiveHash < Hash
+    def initialize(hash = {})
+      super
+      hash.each do |key, value|
+        self[key.downcase] = value
+      end
     end
-  end
 
-  def [](key)
-    super(key.downcase)
-  end
+    def [](key)
+      super(key.downcase)
+    end
 
-  def []=(key, value)
-    super(key.downcase, value)
+    def []=(key, value)
+      super(key.downcase, value)
+    end
   end
 end
diff --git a/lib/audioinfo/flac.rb b/lib/audioinfo/flac.rb
new file mode 100644
index 0000000..dcb8c15
--- /dev/null
+++ b/lib/audioinfo/flac.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'flacinfo'
+
+require_relative 'case_insensitive_hash'
+
+module AudioInfo
+  class Flac < AudioFile
+    def parse(filename)
+      @info = FlacInfo.new(filename)
+      # Unfortunately, FlacInfo doesn't allow us to fiddle inside
+      # their class, so we have to brute force it. Any other
+      # solution (e.g. creating another abstraction or getting
+      # methods) lands up being more messy and brittle.
+      @info.instance_variable_set('@tags', CaseInsensitiveHash.new(@info.tags))
+
+      @artist = get_tag('artist')
+      @album = get_tag('album')
+      @title = get_tag('title')
+      @tracknum = @info.tags['tracknumber'].to_i
+      @date = get_tag('date')
+      @bitrate = 0
+      @length = @info.streaminfo['total_samples'] / @info.streaminfo['samplerate'].to_f
+      @bitrate = File.size(filename).to_f * 8 / @length / 1024 if @length.positive?
+      @info.tags.each do |tagname, _tagvalue|
+        next unless tagname =~ /^musicbrainz_(.+)$/
+
+        @musicbrainz_infos[Regexp.last_match(1)] = get_tag(tagname)
+      end
+      @musicbrainz_infos['trmid'] = @info.tags['musicip_puid']
+      # default_fill_musicbrainz_fields
+    end
+
+    def close
+      return unless @needs_commit
+
+      have_metaflac = system('which metaflac > /dev/null')
+
+      if have_metaflac
+        tags = { 'ARTIST' => @artist,
+                 'ALBUM' => @album,
+                 'TITLE' => @title,
+                 'TRACKNUMBER' => @tracknum }.inject([]) do |t, (key, value)|
+          t + ['--set-tag', "#{key}=#{value}"]
+        end
+        tag_with_shell_command('metaflac', '--remove-all', :src)
+        tag_with_shell_command('metaflac', tags, :src)
+      else
+        super
+      end
+
+      @needs_commit
+    end
+
+    private
+
+    def get_tag(name)
+      @info.tags[name]&.dup&.force_encoding('utf-8')
+    end
+  end
+end
diff --git a/lib/audioinfo/mp3.rb b/lib/audioinfo/mp3.rb
new file mode 100644
index 0000000..360d954
--- /dev/null
+++ b/lib/audioinfo/mp3.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require 'mp3info'
+
+module AudioInfo
+  class Mp3 < AudioFile
+    def parse(filename)
+      @info = Mp3Info.new(filename)
+      default_tag_fill
+
+      # Mp3Info parses additional tags into TXXX
+      if (arr = @info.tag2['TXXX']).is_a?(Array)
+        fields = MUSICBRAINZ_FIELDS.invert
+        arr.each do |val|
+          next unless val =~ /^MusicBrainz (.+)\000(.*)$/
+
+          short_name = fields[Regexp.last_match(1)]
+          next unless short_name
+
+          @musicbrainz_infos[short_name] =
+            Regexp.last_match(2).gsub(String.new("\xEF\xBB\xBF").force_encoding('UTF-8'), '')
+        end
+      end
+
+      # MusicBrainz Track ID is over here:
+      @musicbrainz_infos['trackid'] = @info.tag2['UFID']&.split("\x00")&.last
+
+      @bitrate = @info.bitrate
+      i = @info.tag.tracknum
+      @tracknum = (i.is_a?(Array) ? i.last : i).to_i
+      @length = @info.length.to_i
+      @date = @info.tag['date']
+      @vbr = @info.vbr
+      @info.close
+    rescue Mp3InfoError => e
+      raise AudioInfoError, e.to_s, e.backtrace
+    end
+
+    def close
+      return unless @needs_commit
+
+      Mp3Info.open(@path) do |info|
+        info.tag.artist = @artist
+        info.tag.title = @title
+        info.tag.album = @album
+        info.tag.tracknum = @tracknum
+        if @picture
+          info.tag2.remove_pictures
+          info.tag2.add_picture(File.binread(@picture))
+        end
+      end
+
+      @needs_commit
+    end
+  end
+end
diff --git a/lib/audioinfo/mp4.rb b/lib/audioinfo/mp4.rb
new file mode 100644
index 0000000..fe55cbd
--- /dev/null
+++ b/lib/audioinfo/mp4.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require 'mp4info'
+require 'open3'
+
+module AudioInfo
+  class Mp4 < AudioFile
+    def parse(filename)
+      @extension = 'mp4'
+      @info = MP4Info.open(filename)
+      @artist = @info.ART
+      @album = @info.ALB
+      @title = @info.NAM
+      @tracknum = (t = @info.TRKN) ? t.first : 0
+      @date = @info.DAY
+      @bitrate = @info.BITRATE
+      @length = @info.SECS
+      mapping = MUSICBRAINZ_FIELDS.invert
+
+      faad_info(filename).scan(/^MusicBrainz (.+): (.+)$/) do |match|
+        name, value = match
+        key = mapping[name]
+        next unless key
+
+        @musicbrainz_infos[key] = value.strip.gsub("\u0000", '')
+      end
+    end
+
+    def faad_info(path)
+      output = ''
+      status = nil
+
+      return unless system('which faad > /dev/null')
+
+      Open3.popen3('faad', '-i', path) do |_stdin, _stdout, stderr, wait_thr|
+        output = stderr.read.chomp
+        status = wait_thr.value
+      end
+
+      status.exitstatus.zero? ? output : ''
+    end
+  end
+end
diff --git a/lib/audioinfo/mpc.rb b/lib/audioinfo/mpc.rb
new file mode 100644
index 0000000..1e0c353
--- /dev/null
+++ b/lib/audioinfo/mpc.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require 'apetag'
+require 'mpcinfo'
+
+module AudioInfo
+  class Mpc < Ape
+    def parse(filename)
+      super(filename)
+
+      mpc_info = MpcInfo.new(filename)
+      @bitrate = mpc_info.infos['bitrate'] / 1000
+      @length = mpc_info.infos['length']
+    end
+  end
+end
diff --git a/lib/audioinfo/ogg.rb b/lib/audioinfo/ogg.rb
new file mode 100644
index 0000000..79424b3
--- /dev/null
+++ b/lib/audioinfo/ogg.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require 'ogginfo'
+
+module AudioInfo
+  class Ogg < AudioFile
+    def parse(filename)
+      @info = OggInfo.new(filename)
+      default_fill_musicbrainz_fields
+      default_tag_fill
+      @bitrate = @info.bitrate / 1000
+      @tracknum = @info.tag.tracknumber.to_i
+      @length = @info.length.to_i
+      @date = @info.tag['date']
+      @vbr = true
+      @info.close
+    rescue OggInfoError => e
+      raise AudioInfoError, e.to_s, e.backtrace
+    end
+
+    def close
+      return unless @needs_commit
+
+      OggInfo.open(@path) do |ogg|
+        { 'artist' => @artist,
+          'album' => @album,
+          'title' => @title,
+          'tracknumber' => @tracknum }.each do |k, v|
+          ogg.tag[k] = v.to_s
+        end
+        ogg.picture = @picture if @picture
+      end
+
+      @needs_commit
+    end
+  end
+end
diff --git a/lib/audioinfo/version.rb b/lib/audioinfo/version.rb
index 84bd421..d01a5a4 100644
--- a/lib/audioinfo/version.rb
+++ b/lib/audioinfo/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
-class AudioInfo
+module AudioInfo
   VERSION = '0.5.5'
 end
diff --git a/lib/audioinfo/wav.rb b/lib/audioinfo/wav.rb
new file mode 100644
index 0000000..b31880a
--- /dev/null
+++ b/lib/audioinfo/wav.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require 'wavefile'
+
+module AudioInfo
+  class Wav < AudioFile
+    def parse(filename)
+      @info = WaveFile::Reader.info(filename)
+      @length = @info.duration.hours * 3600 + @info.duration.minutes * 60 + @info.duration.seconds +
+                @info.duration.milliseconds * 0.001
+      @bitrate = File.size(filename) * 8 / @length / 1024
+    end
+  end
+end
diff --git a/lib/audioinfo/wma.rb b/lib/audioinfo/wma.rb
new file mode 100644
index 0000000..ab2ddf7
--- /dev/null
+++ b/lib/audioinfo/wma.rb
@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require 'wmainfo'
+
+module AudioInfo
+  class Wma < AudioFile
+    def parse(filename)
+      @info = WmaInfo.new(filename, encoding: 'utf-8')
+      tags = @info.tags.map { |k, v| [k.strip, v.strip] }.to_h
+
+      @artist = tags['Author']
+      @album = tags['AlbumTitle']
+      @title = tags['Title']
+      @tracknum = tags['TrackNumber'].to_i
+      @date = tags['Year']
+      @bitrate = @info.info['bitrate']
+      @length = @info.info['playtime_seconds']
+
+      info = @info.info.map do |k, v|
+        [
+          k.respond_to?(:strip) ? k.strip : k,
+          v.respond_to?(:strip) ? v.strip : v
+        ]
+      end.to_h
+
+      MUSICBRAINZ_FIELDS.each do |key, original_key|
+        @musicbrainz_infos[key] =
+          info["MusicBrainz/#{original_key.tr(' ', '')}"] ||
+          info["MusicBrainz/#{original_key}"]
+      end
+    end
+  end
+end
diff --git a/test/case_insensitive_hash_test.rb b/test/case_insensitive_hash_test.rb
index 8964ec4..0c170f5 100644
--- a/test/case_insensitive_hash_test.rb
+++ b/test/case_insensitive_hash_test.rb
@@ -4,7 +4,7 @@
 
 class CaseInsensitiveHashTest < MiniTest::Test
   def setup
-    @h = CaseInsensitiveHash.new
+    @h = AudioInfo::CaseInsensitiveHash.new
   end
 
   def test_string_access
@@ -23,7 +23,7 @@ def test_case_insensitive_access
   end
 
   def test_copy_constructor
-    h = CaseInsensitiveHash.new({ 'FOO' => 'bar' })
+    h = AudioInfo::CaseInsensitiveHash.new({ 'FOO' => 'bar' })
     assert_equal 'bar', h['foo']
   end
 end
diff --git a/test/flac_test.rb b/test/flac_test.rb
index 30429a0..32b242b 100644
--- a/test/flac_test.rb
+++ b/test/flac_test.rb
@@ -12,16 +12,12 @@ class FlacTest < MiniTest::Test
   FLAC_FILE = "#{Dir.tmpdir}/ruby-audioinfo-test.flac"
 
   def setup
-    FileUtils.cp(File.join(SUPPORT_DIR, '440Hz-5sec.flac'), FLAC_FILE)
+    FileUtils.cp(File.join(SUPPORT_DIR, 'cantina_band.flac'), FLAC_FILE)
     @i = AudioInfo.new(FLAC_FILE)
   end
 
-  def test_flac_whitelist
-    assert_kind_of FlacInfo, @i.info
-  end
-
-  def test_flac_tags_wrapper
-    assert_kind_of CaseInsensitiveHash, @i.info.tags
+  def test_default_fields
+    assert_equal(DEFAULT_INFO.merge('length' => 3.0, 'bitrate' => 216.0859375), @i.to_h)
   end
 
   def test_flac_writing
diff --git a/test/m4a_test.rb b/test/m4a_test.rb
index 08a9136..59fbf08 100644
--- a/test/m4a_test.rb
+++ b/test/m4a_test.rb
@@ -13,15 +13,14 @@ def setup
     @i = AudioInfo.new(M4A_FILE)
   end
 
-  def test_whitelist
-    assert_kind_of MP4Info, @i.info
-  end
-
-  def test_length
-    assert_in_delta(@i.length, 3)
+  def test_default_fields
+    assert_equal(
+      DEFAULT_INFO.slice('artist', 'length', 'tracknum').merge('bitrate' => 113),
+      @i.to_h.compact
+    )
   end
 
   def test_musicbrainz
-    assert_equal('57c051a1-41db-4764-bfab-ecac5cb3a144', @i.musicbrainz_infos['artistid'])
+    assert_equal(MUSICBRAINZ_INFO, @i.musicbrainz_infos)
   end
 end
diff --git a/test/mp3_test.rb b/test/mp3_test.rb
new file mode 100644
index 0000000..06670b4
--- /dev/null
+++ b/test/mp3_test.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'fileutils'
+require 'tmpdir'
+
+require_relative 'test_helper'
+
+class MP3Test < MiniTest::Test
+  MP3_FILE = "#{Dir.tmpdir}/ruby-audioinfo-test.mp3"
+
+  # mp3 loads both artists while other formats do not
+  ARTIST = "#{MUSICBRAINZ_INFO['artistid']}/4ebf48b9-9b17-43e2-b4aa-7f29b7e608d1"
+
+  def setup
+    FileUtils.cp(File.join(SUPPORT_DIR, 'cantina_band.mp3'), MP3_FILE)
+    @i = AudioInfo.new(MP3_FILE)
+  end
+
+  def test_default_fields
+    assert_equal(DEFAULT_INFO.merge('date' => nil), @i.to_h)
+  end
+
+  def test_musicbrainz
+    assert_equal(
+      MUSICBRAINZ_INFO.merge('artistid' => ARTIST, 'albumartistid' => ARTIST),
+      @i.musicbrainz_infos
+    )
+  end
+end
diff --git a/test/ogg_test.rb b/test/ogg_test.rb
new file mode 100644
index 0000000..5d0b8f5
--- /dev/null
+++ b/test/ogg_test.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'fileutils'
+require 'tmpdir'
+
+require_relative 'test_helper'
+
+class OggTest < MiniTest::Test
+  OGG_FILE = "#{Dir.tmpdir}/ruby-audioinfo-test.ogg"
+
+  def setup
+    FileUtils.cp(File.join(SUPPORT_DIR, 'cantina_band.ogg'), OGG_FILE)
+    @i = AudioInfo.new(OGG_FILE)
+  end
+
+  def test_default_fields
+    assert_equal DEFAULT_INFO.merge('bitrate' => 31.557333333333332), @i.to_h
+  end
+end
diff --git a/test/support/440Hz-5sec.flac b/test/support/440Hz-5sec.flac
deleted file mode 100644
index a23bf90..0000000
Binary files a/test/support/440Hz-5sec.flac and /dev/null differ
diff --git a/test/support/cantina_band.flac b/test/support/cantina_band.flac
new file mode 100644
index 0000000..8c41555
Binary files /dev/null and b/test/support/cantina_band.flac differ
diff --git a/test/support/cantina_band.mp3 b/test/support/cantina_band.mp3
new file mode 100644
index 0000000..124c299
Binary files /dev/null and b/test/support/cantina_band.mp3 differ
diff --git a/test/support/cantina_band.mpc b/test/support/cantina_band.mpc
new file mode 100644
index 0000000..165e383
Binary files /dev/null and b/test/support/cantina_band.mpc differ
diff --git a/test/support/cantina_band.ogg b/test/support/cantina_band.ogg
new file mode 100644
index 0000000..d1c8d30
Binary files /dev/null and b/test/support/cantina_band.ogg differ
diff --git a/test/support/cantina_band.wav b/test/support/cantina_band.wav
new file mode 100644
index 0000000..af1d918
Binary files /dev/null and b/test/support/cantina_band.wav differ
diff --git a/test/support/cantina_band.wma b/test/support/cantina_band.wma
new file mode 100644
index 0000000..7126766
Binary files /dev/null and b/test/support/cantina_band.wma differ
diff --git a/test/support/piano2.wav b/test/support/piano2.wav
deleted file mode 100644
index 12348ef..0000000
Binary files a/test/support/piano2.wav and /dev/null differ
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 0f6b9cf..ac60751 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -20,3 +20,21 @@
 require 'minitest/rg'
 
 SUPPORT_DIR = File.expand_path('support', File.dirname(__FILE__))
+
+DEFAULT_INFO = {
+  'artist'   => 'Martin Spitznagel & Bryan Wright',
+  'album'    => 'Star Wars: Cantina Band in Ragtime',
+  'title'    => 'Star Wars: Cantina Band in Ragtime',
+  'tracknum' => 1,
+  'date'     => '2011-03-29',
+  'length'   => 3,
+  'bitrate'  => 25
+}.freeze
+
+MUSICBRAINZ_INFO = {
+  'albumtype'     => 'single',
+  'albumid'       => 'c357ac93-8896-4486-9630-05ae04c43345',
+  'artistid'      => '57c051a1-41db-4764-bfab-ecac5cb3a144',
+  'albumartistid' => '57c051a1-41db-4764-bfab-ecac5cb3a144',
+  'trackid'       => '608be633-8a2b-4b90-b745-e38cae815c20'
+}.freeze
diff --git a/test/wav_test.rb b/test/wav_test.rb
index a566889..56421fb 100644
--- a/test/wav_test.rb
+++ b/test/wav_test.rb
@@ -9,15 +9,15 @@ class TestWav < MiniTest::Test
   WAV_FILE = "#{Dir.tmpdir}/ruby-audioinfo-test.wav"
 
   def setup
-    FileUtils.cp(File.join(SUPPORT_DIR, 'piano2.wav'), WAV_FILE)
+    FileUtils.cp(File.join(SUPPORT_DIR, 'cantina_band.wav'), WAV_FILE)
     @i = AudioInfo.new(WAV_FILE)
   end
 
-  def test_wav_whitelist
-    assert_kind_of WaveFile::Info, @i.info
+  def test_default_fields
+    assert_equal({ 'length' => 3.0, 'bitrate' => 352.8645833333333 }, @i.to_h.compact)
   end
 
-  def test_wav_length
-    assert_in_delta(@i.length, 6.306)
+  def test_musicbrainz
+    assert_equal({}, @i.musicbrainz_infos)
   end
 end
diff --git a/test/wma_test.rb b/test/wma_test.rb
new file mode 100644
index 0000000..b9e85d0
--- /dev/null
+++ b/test/wma_test.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'fileutils'
+require 'tmpdir'
+
+require_relative 'test_helper'
+
+class WmaTest < MiniTest::Test
+  WMA_FILE = "#{Dir.tmpdir}/ruby-audioinfo-test.wma"
+
+  def setup
+    FileUtils.cp(File.join(SUPPORT_DIR, 'cantina_band.wma'), WMA_FILE)
+    @i = AudioInfo.new(WMA_FILE)
+  end
+
+  def test_default_fields
+    assert_equal(DEFAULT_INFO.merge('bitrate' => 24, 'length' => 4), @i.to_h)
+  end
+
+  def test_musicbrainz
+    assert_equal MUSICBRAINZ_INFO.sort, @i.musicbrainz_infos.sort
+  end
+end