You can't really do video detection it in real time and properly, without overheating the cheap device. On the SaaS we did we use a recorded segment of video so we can analyse it afterwards, check the colour changes in the face of the subject and try estimate heartbeat with loose accuracy. More like high, Normal, Low after taking a few seconds as base.
The idea of the ADHD device was just a cheap hack done in a day for myself.
Not a product or commercial as I don't feel claiming it can do to others what I looks like does to me.
Happy to share here FREE ; )