diff --git a/beets/mediafile.py b/beets/mediafile.py
index 4701600d5..e80cd65d9 100644
--- a/beets/mediafile.py
+++ b/beets/mediafile.py
@@ -592,7 +592,7 @@ class MP4StorageStyle(StorageStyle):
 
     def serialize(self, value):
         value = super(MP4StorageStyle, self).serialize(value)
-        if self.key.startswith(b'----:') and isinstance(value, unicode):
+        if self.key.startswith('----:') and isinstance(value, unicode):
             value = value.encode('utf8')
         return value
 
@@ -667,7 +667,7 @@ class MP4ImageStorageStyle(MP4ListStorageStyle):
     """Store images as MPEG-4 image atoms. Values are `Image` objects.
     """
     def __init__(self, **kwargs):
-        super(MP4ImageStorageStyle, self).__init__(key=b'covr', **kwargs)
+        super(MP4ImageStorageStyle, self).__init__(key='covr', **kwargs)
 
     def deserialize(self, data):
         return Image(data)
@@ -1547,25 +1547,25 @@ class MediaFile(object):
 
     title = MediaField(
         MP3StorageStyle('TIT2'),
-        MP4StorageStyle(b"\xa9nam"),
+        MP4StorageStyle('\xa9nam'),
         StorageStyle('TITLE'),
         ASFStorageStyle('Title'),
     )
     artist = MediaField(
         MP3StorageStyle('TPE1'),
-        MP4StorageStyle(b"\xa9ART"),
+        MP4StorageStyle('\xa9ART'),
         StorageStyle('ARTIST'),
         ASFStorageStyle('Author'),
     )
     album = MediaField(
         MP3StorageStyle('TALB'),
-        MP4StorageStyle(b"\xa9alb"),
+        MP4StorageStyle('\xa9alb'),
         StorageStyle('ALBUM'),
         ASFStorageStyle('WM/AlbumTitle'),
     )
     genres = ListMediaField(
         MP3ListStorageStyle('TCON'),
-        MP4ListStorageStyle(b"\xa9gen"),
+        MP4ListStorageStyle('\xa9gen'),
         ListStorageStyle('GENRE'),
         ASFStorageStyle('WM/Genre'),
     )
@@ -1573,19 +1573,19 @@ class MediaFile(object):
 
     composer = MediaField(
         MP3StorageStyle('TCOM'),
-        MP4StorageStyle(b"\xa9wrt"),
+        MP4StorageStyle('\xa9wrt'),
         StorageStyle('COMPOSER'),
         ASFStorageStyle('WM/Composer'),
     )
     grouping = MediaField(
         MP3StorageStyle('TIT1'),
-        MP4StorageStyle(b"\xa9grp"),
+        MP4StorageStyle('\xa9grp'),
         StorageStyle('GROUPING'),
         ASFStorageStyle('WM/ContentGroupDescription'),
     )
     track = MediaField(
         MP3SlashPackStorageStyle('TRCK', pack_pos=0),
-        MP4TupleStorageStyle(b'trkn', index=0),
+        MP4TupleStorageStyle('trkn', index=0),
         StorageStyle('TRACK'),
         StorageStyle('TRACKNUMBER'),
         ASFStorageStyle('WM/TrackNumber'),
@@ -1593,7 +1593,7 @@ class MediaFile(object):
     )
     tracktotal = MediaField(
         MP3SlashPackStorageStyle('TRCK', pack_pos=1),
-        MP4TupleStorageStyle(b'trkn', index=1),
+        MP4TupleStorageStyle('trkn', index=1),
         StorageStyle('TRACKTOTAL'),
         StorageStyle('TRACKC'),
         StorageStyle('TOTALTRACKS'),
@@ -1602,7 +1602,7 @@ class MediaFile(object):
     )
     disc = MediaField(
         MP3SlashPackStorageStyle('TPOS', pack_pos=0),
-        MP4TupleStorageStyle(b'disk', index=0),
+        MP4TupleStorageStyle('disk', index=0),
         StorageStyle('DISC'),
         StorageStyle('DISCNUMBER'),
         ASFStorageStyle('WM/PartOfSet'),
@@ -1610,7 +1610,7 @@ class MediaFile(object):
     )
     disctotal = MediaField(
         MP3SlashPackStorageStyle('TPOS', pack_pos=1),
-        MP4TupleStorageStyle(b'disk', index=1),
+        MP4TupleStorageStyle('disk', index=1),
         StorageStyle('DISCTOTAL'),
         StorageStyle('DISCC'),
         StorageStyle('TOTALDISCS'),
@@ -1619,13 +1619,13 @@ class MediaFile(object):
     )
     lyrics = MediaField(
         MP3DescStorageStyle(key='USLT'),
-        MP4StorageStyle(b"\xa9lyr"),
+        MP4StorageStyle('\xa9lyr'),
         StorageStyle('LYRICS'),
         ASFStorageStyle('WM/Lyrics'),
     )
     comments = MediaField(
         MP3DescStorageStyle(key='COMM'),
-        MP4StorageStyle(b"\xa9cmt"),
+        MP4StorageStyle('\xa9cmt'),
         StorageStyle('DESCRIPTION'),
         StorageStyle('COMMENT'),
         ASFStorageStyle('WM/Comments'),
@@ -1633,111 +1633,111 @@ class MediaFile(object):
     )
     bpm = MediaField(
         MP3StorageStyle('TBPM'),
-        MP4StorageStyle(b'tmpo', as_type=int),
+        MP4StorageStyle('tmpo', as_type=int),
         StorageStyle('BPM'),
         ASFStorageStyle('WM/BeatsPerMinute'),
         out_type=int,
     )
     comp = MediaField(
         MP3StorageStyle('TCMP'),
-        MP4BoolStorageStyle(b'cpil'),
+        MP4BoolStorageStyle('cpil'),
         StorageStyle('COMPILATION'),
         ASFStorageStyle('WM/IsCompilation', as_type=bool),
         out_type=bool,
     )
     albumartist = MediaField(
         MP3StorageStyle('TPE2'),
-        MP4StorageStyle(b'aART'),
+        MP4StorageStyle('aART'),
         StorageStyle('ALBUM ARTIST'),
         StorageStyle('ALBUMARTIST'),
         ASFStorageStyle('WM/AlbumArtist'),
     )
     albumtype = MediaField(
         MP3DescStorageStyle(u'MusicBrainz Album Type'),
-        MP4StorageStyle(b'----:com.apple.iTunes:MusicBrainz Album Type'),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Album Type'),
         StorageStyle('MUSICBRAINZ_ALBUMTYPE'),
         ASFStorageStyle('MusicBrainz/Album Type'),
     )
     label = MediaField(
         MP3StorageStyle('TPUB'),
-        MP4StorageStyle(b'----:com.apple.iTunes:Label'),
-        MP4StorageStyle(b'----:com.apple.iTunes:publisher'),
+        MP4StorageStyle('----:com.apple.iTunes:Label'),
+        MP4StorageStyle('----:com.apple.iTunes:publisher'),
         StorageStyle('LABEL'),
         StorageStyle('PUBLISHER'),  # Traktor
         ASFStorageStyle('WM/Publisher'),
     )
     artist_sort = MediaField(
         MP3StorageStyle('TSOP'),
-        MP4StorageStyle(b"soar"),
+        MP4StorageStyle('soar'),
         StorageStyle('ARTISTSORT'),
         ASFStorageStyle('WM/ArtistSortOrder'),
     )
     albumartist_sort = MediaField(
         MP3DescStorageStyle(u'ALBUMARTISTSORT'),
-        MP4StorageStyle(b"soaa"),
+        MP4StorageStyle('soaa'),
         StorageStyle('ALBUMARTISTSORT'),
         ASFStorageStyle('WM/AlbumArtistSortOrder'),
     )
     asin = MediaField(
         MP3DescStorageStyle(u'ASIN'),
-        MP4StorageStyle(b"----:com.apple.iTunes:ASIN"),
+        MP4StorageStyle('----:com.apple.iTunes:ASIN'),
         StorageStyle('ASIN'),
         ASFStorageStyle('MusicBrainz/ASIN'),
     )
     catalognum = MediaField(
         MP3DescStorageStyle(u'CATALOGNUMBER'),
-        MP4StorageStyle(b"----:com.apple.iTunes:CATALOGNUMBER"),
+        MP4StorageStyle('----:com.apple.iTunes:CATALOGNUMBER'),
         StorageStyle('CATALOGNUMBER'),
         ASFStorageStyle('WM/CatalogNo'),
     )
     disctitle = MediaField(
         MP3StorageStyle('TSST'),
-        MP4StorageStyle(b"----:com.apple.iTunes:DISCSUBTITLE"),
+        MP4StorageStyle('----:com.apple.iTunes:DISCSUBTITLE'),
         StorageStyle('DISCSUBTITLE'),
         ASFStorageStyle('WM/SetSubTitle'),
     )
     encoder = MediaField(
         MP3StorageStyle('TENC'),
-        MP4StorageStyle(b"\xa9too"),
+        MP4StorageStyle('\xa9too'),
         StorageStyle('ENCODEDBY'),
         StorageStyle('ENCODER'),
         ASFStorageStyle('WM/EncodedBy'),
     )
     script = MediaField(
         MP3DescStorageStyle(u'Script'),
-        MP4StorageStyle(b"----:com.apple.iTunes:SCRIPT"),
+        MP4StorageStyle('----:com.apple.iTunes:SCRIPT'),
         StorageStyle('SCRIPT'),
         ASFStorageStyle('WM/Script'),
     )
     language = MediaField(
         MP3StorageStyle('TLAN'),
-        MP4StorageStyle(b"----:com.apple.iTunes:LANGUAGE"),
+        MP4StorageStyle('----:com.apple.iTunes:LANGUAGE'),
         StorageStyle('LANGUAGE'),
         ASFStorageStyle('WM/Language'),
     )
     country = MediaField(
         MP3DescStorageStyle('MusicBrainz Album Release Country'),
-        MP4StorageStyle(b"----:com.apple.iTunes:MusicBrainz "
-                        b"Album Release Country"),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz '
+                        'Album Release Country'),
         StorageStyle('RELEASECOUNTRY'),
         ASFStorageStyle('MusicBrainz/Album Release Country'),
     )
     albumstatus = MediaField(
         MP3DescStorageStyle(u'MusicBrainz Album Status'),
-        MP4StorageStyle(b"----:com.apple.iTunes:MusicBrainz Album Status"),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Album Status'),
         StorageStyle('MUSICBRAINZ_ALBUMSTATUS'),
         ASFStorageStyle('MusicBrainz/Album Status'),
     )
     media = MediaField(
         MP3StorageStyle('TMED'),
-        MP4StorageStyle(b"----:com.apple.iTunes:MEDIA"),
+        MP4StorageStyle('----:com.apple.iTunes:MEDIA'),
         StorageStyle('MEDIA'),
         ASFStorageStyle('WM/Media'),
     )
     albumdisambig = MediaField(
         # This tag mapping was invented for beets (not used by Picard, etc).
         MP3DescStorageStyle(u'MusicBrainz Album Comment'),
-        MP4StorageStyle(b"----:com.apple.iTunes:MusicBrainz Album Comment"),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Album Comment'),
         StorageStyle('MUSICBRAINZ_ALBUMCOMMENT'),
         ASFStorageStyle('MusicBrainz/Album Comment'),
     )
@@ -1745,7 +1745,7 @@ class MediaFile(object):
     # Release date.
     date = DateField(
         MP3StorageStyle('TDRC'),
-        MP4StorageStyle(b"\xa9day"),
+        MP4StorageStyle('\xa9day'),
         StorageStyle('DATE'),
         ASFStorageStyle('WM/Year'),
         year=(StorageStyle('YEAR'),))
@@ -1757,7 +1757,7 @@ class MediaFile(object):
     # *Original* release date.
     original_date = DateField(
         MP3StorageStyle('TDOR'),
-        MP4StorageStyle(b'----:com.apple.iTunes:ORIGINAL YEAR'),
+        MP4StorageStyle('----:com.apple.iTunes:ORIGINAL YEAR'),
         StorageStyle('ORIGINALDATE'),
         ASFStorageStyle('WM/OriginalReleaseYear'))
 
@@ -1768,13 +1768,13 @@ class MediaFile(object):
     # Nonstandard metadata.
     artist_credit = MediaField(
         MP3DescStorageStyle(u'Artist Credit'),
-        MP4StorageStyle(b"----:com.apple.iTunes:Artist Credit"),
+        MP4StorageStyle('----:com.apple.iTunes:Artist Credit'),
         StorageStyle('ARTIST_CREDIT'),
         ASFStorageStyle('beets/Artist Credit'),
     )
     albumartist_credit = MediaField(
         MP3DescStorageStyle(u'Album Artist Credit'),
-        MP4StorageStyle(b"----:com.apple.iTunes:Album Artist Credit"),
+        MP4StorageStyle('----:com.apple.iTunes:Album Artist Credit'),
         StorageStyle('ALBUMARTIST_CREDIT'),
         ASFStorageStyle('beets/Album Artist Credit'),
     )
@@ -1788,31 +1788,31 @@ class MediaFile(object):
     # MusicBrainz IDs.
     mb_trackid = MediaField(
         MP3UFIDStorageStyle(owner='http://musicbrainz.org'),
-        MP4StorageStyle(b'----:com.apple.iTunes:MusicBrainz Track Id'),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Track Id'),
         StorageStyle('MUSICBRAINZ_TRACKID'),
         ASFStorageStyle('MusicBrainz/Track Id'),
     )
     mb_albumid = MediaField(
         MP3DescStorageStyle(u'MusicBrainz Album Id'),
-        MP4StorageStyle(b'----:com.apple.iTunes:MusicBrainz Album Id'),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Album Id'),
         StorageStyle('MUSICBRAINZ_ALBUMID'),
         ASFStorageStyle('MusicBrainz/Album Id'),
     )
     mb_artistid = MediaField(
         MP3DescStorageStyle(u'MusicBrainz Artist Id'),
-        MP4StorageStyle(b'----:com.apple.iTunes:MusicBrainz Artist Id'),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Artist Id'),
         StorageStyle('MUSICBRAINZ_ARTISTID'),
         ASFStorageStyle('MusicBrainz/Artist Id'),
     )
     mb_albumartistid = MediaField(
         MP3DescStorageStyle(u'MusicBrainz Album Artist Id'),
-        MP4StorageStyle(b'----:com.apple.iTunes:MusicBrainz Album Artist Id'),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Album Artist Id'),
         StorageStyle('MUSICBRAINZ_ALBUMARTISTID'),
         ASFStorageStyle('MusicBrainz/Album Artist Id'),
     )
     mb_releasegroupid = MediaField(
         MP3DescStorageStyle(u'MusicBrainz Release Group Id'),
-        MP4StorageStyle(b'----:com.apple.iTunes:MusicBrainz Release Group Id'),
+        MP4StorageStyle('----:com.apple.iTunes:MusicBrainz Release Group Id'),
         StorageStyle('MUSICBRAINZ_RELEASEGROUPID'),
         ASFStorageStyle('MusicBrainz/Release Group Id'),
     )
@@ -1820,13 +1820,13 @@ class MediaFile(object):
     # Acoustid fields.
     acoustid_fingerprint = MediaField(
         MP3DescStorageStyle(u'Acoustid Fingerprint'),
-        MP4StorageStyle(b'----:com.apple.iTunes:Acoustid Fingerprint'),
+        MP4StorageStyle('----:com.apple.iTunes:Acoustid Fingerprint'),
         StorageStyle('ACOUSTID_FINGERPRINT'),
         ASFStorageStyle('Acoustid/Fingerprint'),
     )
     acoustid_id = MediaField(
         MP3DescStorageStyle(u'Acoustid Id'),
-        MP4StorageStyle(b'----:com.apple.iTunes:Acoustid Id'),
+        MP4StorageStyle('----:com.apple.iTunes:Acoustid Id'),
         StorageStyle('ACOUSTID_ID'),
         ASFStorageStyle('Acoustid/Id'),
     )
@@ -1847,11 +1847,11 @@ class MediaFile(object):
             id3_lang='eng'
         ),
         MP4StorageStyle(
-            b'----:com.apple.iTunes:replaygain_track_gain',
-            float_places=2, suffix=b' dB'
+            '----:com.apple.iTunes:replaygain_track_gain',
+            float_places=2, suffix=' dB'
         ),
         MP4SoundCheckStorageStyle(
-            b'----:com.apple.iTunes:iTunNORM',
+            '----:com.apple.iTunes:iTunNORM',
             index=0
         ),
         StorageStyle(
@@ -1874,7 +1874,7 @@ class MediaFile(object):
             float_places=2, suffix=u' dB'
         ),
         MP4SoundCheckStorageStyle(
-            b'----:com.apple.iTunes:iTunNORM',
+            '----:com.apple.iTunes:iTunNORM',
             index=1
         ),
         StorageStyle(
@@ -1902,11 +1902,11 @@ class MediaFile(object):
             id3_lang='eng'
         ),
         MP4StorageStyle(
-            b'----:com.apple.iTunes:replaygain_track_peak',
+            '----:com.apple.iTunes:replaygain_track_peak',
             float_places=6
         ),
         MP4SoundCheckStorageStyle(
-            b'----:com.apple.iTunes:iTunNORM',
+            '----:com.apple.iTunes:iTunNORM',
             index=1
         ),
         StorageStyle(u'REPLAYGAIN_TRACK_PEAK', float_places=6),
@@ -1923,7 +1923,7 @@ class MediaFile(object):
             float_places=6
         ),
         MP4StorageStyle(
-            b'----:com.apple.iTunes:replaygain_album_peak',
+            '----:com.apple.iTunes:replaygain_album_peak',
             float_places=6
         ),
         StorageStyle(u'REPLAYGAIN_ALBUM_PEAK', float_places=6),
@@ -1933,7 +1933,7 @@ class MediaFile(object):
 
     initial_key = MediaField(
         MP3StorageStyle('TKEY'),
-        MP4StorageStyle(b'----:com.apple.iTunes:initialkey'),
+        MP4StorageStyle('----:com.apple.iTunes:initialkey'),
         StorageStyle('INITIALKEY'),
         ASFStorageStyle('INITIALKEY'),
     )
diff --git a/test/test_mediafile.py b/test/test_mediafile.py
index 180249d91..c38921360 100644
--- a/test/test_mediafile.py
+++ b/test/test_mediafile.py
@@ -297,10 +297,10 @@ class GenreListTestMixin(object):
 
 
 field_extension = MediaField(
-    MP3DescStorageStyle(b'customtag'),
-    MP4StorageStyle(b'----:com.apple.iTunes:customtag'),
-    StorageStyle(b'customtag'),
-    ASFStorageStyle(b'customtag'),
+    MP3DescStorageStyle('customtag'),
+    MP4StorageStyle('----:com.apple.iTunes:customtag'),
+    StorageStyle('customtag'),
+    ASFStorageStyle('customtag'),
 )