How to use the av.packet.Packet function in av

def iter_raw_frames(path, packet_sizes, ctx):
    with open(path, 'rb') as f:
        for i, size in enumerate(packet_sizes):
            packet = Packet(size)
            read_size = f.readinto(packet)
            assert size
            assert read_size == size
            print i + 1, size, read_size
            if not read_size:
                break
            for frame in ctx.decode(packet):
                print '   ', frame
                yield frame
        print 'flushing...'
        while True:
            frames = ctx.decode(None)
            for frame in frames:
                print '   ', frame
                yield frame
            if not frames:

frame_count,
                codec_name if codec_name != 'mjpeg' else 'jpg',
            ))
            path_list.append(path)
            with open(path, 'wb') as f:
                f.write(new_packet)
            frame_count += 1
            if frame_count > 5:
                break

        ctx = av.Codec(codec_name, 'r').create()

        for path in path_list:
            with open(path, 'rb') as f:
                size = os.fstat(f.fileno()).st_size
                packet = Packet(size)
                size = f.readinto(packet)
                frame = ctx.decode(packet)[0]
                self.assertEqual(frame.width, width)
                self.assertEqual(frame.height, height)
                self.assertEqual(frame.format.name, pix_fmt)

def decode(self, data):
        packet = av.packet.Packet(data)
        return self._decoder.decode(packet)