another import error related to embedding art

Traceback (most recent call last):
  File "/usr/local/bin/beet", line 9, in <module>
    load_entry_point('beets==1.3.11', 'console_scripts', 'beet')()
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/ui/__init__.py", line 953, in main
    _raw_main(args)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/ui/__init__.py", line 943, in _raw_main
    subcommand.func(lib, suboptions, subargs)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/ui/commands.py", line 868, in import_func
    import_files(lib, paths, query)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/ui/commands.py", line 845, in import_files
    session.run()
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/importer.py", line 316, in run
    pl.run_parallel(QUEUE_SIZE)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/util/pipeline.py", line 347, in run
    self.coro.send(msg)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/util/pipeline.py", line 160, in coro
    task = func(*(args + (task,)))
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/importer.py", line 1361, in manipulate_files
    task.finalize(session)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/importer.py", line 517, in finalize
    self._emit_imported(session.lib)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/importer.py", line 547, in _emit_imported
    plugins.send('album_imported', lib=lib, album=self.album)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/plugins.py", line 465, in send
    result = handler(**args)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beetsplug/embedart.py", line 132, in album_imported
    self.embed_album(album, max_width, True)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beetsplug/embedart.py", line 179, in embed_album
    thresh, ifempty, as_album=True)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beetsplug/embedart.py", line 156, in embed_item
    item.try_write(itempath)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/library.py", line 543, in try_write
    self.write(path)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/library.py", line 525, in write
    mediafile.update(tags)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/mediafile.py", line 1477, in update
    setattr(self, field, dict[field])
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/mediafile.py", line 1110, in __set__
    style.set_list(mediafile.mgfile, values)
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/mediafile.py", line 523, in set_list
    self.store(mutagen_file, [self.serialize(value) for value in values])
  File "/Library/Python/2.7/site-packages/beets-1.3.11-py2.7.egg/beets/mediafile.py", line 657, in serialize
    raise ValueError('MP4 files only supports PNG and JPEG images')
ValueError: MP4 files only supports PNG and JPEG images