'Return the offset of the next \'ÿ\' byte in *stream* starting with
the byte at offset *start*. Returns *start* if the byte at that
offset is a hex 255; it does not necessarily advance in the stream.'

def _offset_of_next_ff_byte(self, start):

    self._stream.seek(start)
    byte_ = self._read_byte()
    while (byte_ != '\xff'):
        byte_ = self._read_byte()
    offset_of_ff_byte = (self._stream.tell() - 1)
    return offset_of_ff_byte
