def find_offset(fn:str):
    """\
Finds the offset for the XSPD block. At the moment this just searches
the file for the XSPD header, but in future this will use the offsets
of the other blocks to seek to the correct location.
"""
    BS = 4194304
    with open(fn, "rb") as wad:
        count = 0
        b = wad.read(BS)
        while len(b) > 0:
            if b"XSPD" in b:
                return b.find(b"XSPD") + BS*count
            count += 1