fix: shell execute problem on Linux and macOS when calling mp4box

src/mp4.py

@@ -194,6 +194,11 @@ async def write_metadata(song: bytes, metadata: SongMetadata, embed_metadata: li
         time = datetime.strptime(metadata.created, "%Y-%m-%d").strftime("%d/%m/%Y")
     else:
         time = ""
+    if if_shell():
+        subprocess.run(
+            f"mp4box -time {time} -mtime {time} -name 1={metadata.title} -itags tool=:cover={absolute_cover_path}:{metadata.to_itags_params(embed_metadata)} {song_name.absolute()}",
+        stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, shell=if_shell())
+    else:
         subprocess.run(["mp4box", "-time", time, "-mtime", time, "-name", f"1={metadata.title}", "-itags",
                         ":".join(["tool=", f"cover={absolute_cover_path}",
                                   metadata.to_itags_params(embed_metadata)]),