Spotify ad muter in Python

mute.py

import os, dbus
from time import sleep
from subprocess import call

session_bus = dbus.SessionBus()
spotify_bus = session_bus.get_object("org.mpris.MediaPlayer2.spotify", "/org/mpris/MediaPlayer2")
spotify_properties = dbus.Interface(spotify_bus, "org.freedesktop.DBus.Properties")

while True:
  metadata = spotify_properties.Get("org.mpris.MediaPlayer2.Player", "Metadata")
  playback_status = str(spotify_properties.Get("org.mpris.MediaPlayer2.Player", "PlaybackStatus"))

  if playback_status == 'Playing':
    song_title = str(metadata['xesam:title'])
    song_length = int(metadata['mpris:length']) / 1000000
    if song_title.strip() == 'Spotify' or (song_length > 29 and song_length < 31):
      call(['amixer', '-D', 'pulse', 'set', 'Master', 'mute'], stdout=open(os.devnull, 'w'))
      sleep(30)
      call(['amixer', '-D', 'pulse', 'set', 'Master', 'unmute'], stdout=open(os.devnull, 'w'))
  sleep(0.5)