Actually just removed that stuff and seems to be faster, there is a qrtun_async.py script now with no seq/ack. That being said, my concern was that if creating/displaying the qr code was much faster than detecting/decoding, and a lot of packets were coming in at once, you could maybe display multiple packets/qrcodes before the other side was able to decode the first one. That would result in drops of course which should be re transmitted though, so I guess its okay.

You could also decouple image capture and packet processing, so that if the former starts to run ahead, you can buffer until the latter catches up. NICs do this a lot, for much the same benefit.

I'm not great with Python, but your code seems quite legible, and it doesn't look like there's any buffering or backpressure in place right now - which is perfectly reasonable for a fantastic proof of concept like this! Just a thought for when you next get around to hacking on it.