'Merge Album objs by copying missing items from albums in the tail
to the head album.
Return same number of albums, with the head album modified.'

def _merge_albums(self, objs):

    ids = [i.mb_trackid for i in objs[0].items()]
    for o in objs[1:]:
        for i in o.items():
            if (i.mb_trackid not in ids):
                missing = Item.from_path(i.path)
                missing.album_id = objs[0].id
                missing.add(i._db)
                self._log.debug(u'item    {0}    missing    from    album    {1}:    merging    from    {2}    into    {3}', missing, objs[0], displayable_path(o.path), displayable_path(missing.destination()))
                missing.move(copy=True)
    return objs
