How to load albumart of the song downloaded by other music apps

Question

I am working on a Music Player.Using

MediaStore.Audio.Media.EXTERNAL_CONTENT_URI

I can retrieve the information of music downloaded by other Music apps(if sync to the local).But I still can't get **the album artwork ** by the same way I get the artwork of local music -

 Uri artworkUri = Uri.parse("content://media/external/audio/albumart");
 Uri albumArtUri = ContentUris.withAppendedId(artworkUri, albumId);

Since I already retrieve the music info , why can't I get the artwork by the same old way?It's sure that these songs has their albumart when other apps playing... Ps: and what's the different about this Uri

"content://media/external/audio/media/" + songId + "/albumart"

Any suggestions/hints are all appreciated!