Record the file pointer position of each frame

def determine_packet_positions(self):
        """Record the file pointer position of each frame"""
        print("Analysing file...")
        self.rewind_file()
        with ignored(struct.error):
            while True:
                pointer_position = self.blob_file.tell()
                length = struct.unpack('<i', self.blob_file.read(4))[0]
                self.packet_positions.append(pointer_position)
                self.blob_file.seek(length, 1)
        self.rewind_file()
        print("Found {0} CLB UDP packets.".format(len(self.packet_positions)))