'Calculate the offset to the Xing header from the start of the
MPEG header including sync based on the MPEG header\'s content.'

@classmethod
def get_offset(cls, info):

    assert (info.layer == 3)
    if (info.version == 1):
        if (info.mode != 3):
            return 36
        else:
            return 21
    elif (info.mode != 3):
        return 21
    else:
        return 13
