• If it is possible to control the speed of a treadmill with Home Assistant:

Xiaomi treadmills can be controlled by user code

• it should also be possible to measure the speed of a treadmill with Home Assistant:

Further development of the fellnr treadmill calibration

• but is there no method which is more robust than a camera which records color dots on a treatmill?

• Unfortunately, we do not have standardized speed sensors for treadmills, like those for bike speed and cadence. What bike speed and cadence sensors actually measure is shown here:

https://bicycles.stackexchange.com/questions/9021/what-does-a-cyclocomputer-actually-measure-for-calculating-the-speed-of-the-bike

• The best sensors for treadmills are already reviewed here:

How can we get the most accurate readings from a treadmill?

• But these sensors are not sensors which have for instance an MQTT interface, which would allow to connect them easily for instance to Home Assistant. Home Assistant or InfluxDB is a new platform for these kind of sensors. Developers welcome to solve this problem.