How can I find the flow velocity of smoke in this video?

I guess I just have no idea where to even start so any help would be massively appreciated!

I would only need to find it before the smoke meets the middle, i.e. before it becomes massively turbulent.

[Vishnu Sreekumar]

https://www.mathworks.com/help/imaq/examples/live-motion-detection-using-optical-flow.html