Mutagen: How can I "correctly" embed album art into mp3 file so that I can see the pitcure display as file icon

I am trying to convert flac files to mp3 format, using pydub for conversion and mutagen for tags and album art copy.

Convert a flac file to a 320Kbps mp3:

from pydub import AudioSegment

path_flac  = 'mc_test/from/01 Lapislazuli.flac'
path_mp3   = 'mc_test/to/01 Lapislazuli.mp3'
flac_audio = AudioSegment.from_file(path_flac, format="flac")
flac_audio.export(path_mp3, format="mp3", bitrate='320K')

Load album art image from flac file and embed it into mp3 file (follow this question):

from mutagen.flac import FLAC
from mutagen.mp3 import MP3
from mutagen.id3 import ID3, APIC

file = FLAC(path_flac)
art = file.pictures[0].data

audio = MP3(path_mp3, ID3=ID3)    
audio.tags.add(
    APIC(
        encoding=3, # 3 is for utf-8
        mime='image/png', # image/jpeg or image/png
        type=3, # 3 is for the cover image
        desc=u'Cover',
        data=art
    )
)
audio.save()

I successfully embed the album art into the mp3 file, and the picture showed in players such as foobar and MPC, but didn't correctly showed in file icon. If I convert the file via foobar, it correctly showed, but didn't work with mutagen.

Does anyone knows how to make the album art correctly showed as icon?

Thanks for suggestion from @diggusbickus , I found and compared differences between mp3 file generated from foobar and pydub. The difference is encoding.

In pydub-converted file, which tags and album art were added by mutagen:

path_mp3 = 'mc_test/to/01 Lapislazuli.mp3'
file_mutagen = File(path_mp3)
file_mutagen.tags['APIC:'].encoding

It shows <Encoding.UTF8: 3>, which probably came from audio.tags.add(APIC(encoding=3)) above.

In foobar-converted file:

path_mp3_foobar = 'mc_test/foobar/01 Lapislazuli.mp3'
file_foobar = File(path_mp3_foobar)
file_foobar.tags['APIC:'].encoding

shows <Encoding.LATIN1: 0>

So I change my setting to audio.tags.add(APIC(encoding=0)) while embeding image, and it works, now I can see album art as a icon preview image. Also I do a little survey to check if other encoding number works, album art would correctly showed with encoding=0, 1 and 2.