images: use jpg extensions for jpeg files everywhere

fix #2254

beets/art.py

@@ -193,7 +193,7 @@ def extract(log, outpath, item):
         return
 
     # Add an extension to the filename.
-    ext = imghdr.what(None, h=art)
+    ext = mediafile.image_extension(art)
     if not ext:
         log.warning(u'Unknown image type in {0}.',
                     displayable_path(item.path))

beets/mediafile.py

@@ -59,6 +59,7 @@ import enum
 
 from beets import logging
 from beets.util import displayable_path, syspath, as_string
+from beets.util.collections import IdentityUnlessDict
 import six
 
 
@@ -81,6 +82,8 @@ TYPES = {
     'aiff': 'AIFF',
 }
 
+PREFERRED_IMAGE_EXTENSIONS = IdentityUnlessDict({'jpeg': 'jpg'})
+
 
 # Exceptions.
 
@@ -351,6 +354,10 @@ def image_mime_type(data):
         return 'image/x-{0}'.format(kind)
 
 
+def image_extension(data):
+    return PREFERRED_IMAGE_EXTENSIONS[_imghdr_what_wrapper(data)]
+
+
 class ImageType(enum.Enum):
     """Indicates the kind of an `Image` stored in a file's tag.
     """

beets/util/collections.py

@@ -0,0 +1,27 @@
+# -*- coding: utf-8 -*-
+# This file is part of beets.
+# Copyright 2016, Adrian Sampson.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+"""Custom collections classes
+"""
+
+
+class IdentityUnlessDict(dict):
+    """A dictionary which is "transparent" (maps keys to themselves) for all
+    keys not in it.
+    """
+    def __getitem__(self, key):
+        try:
+            return dict.__getitem__(self, key)
+        except KeyError:
+            return key