How to detect real time sound onsets?
My guess is that the currently popular and new and likely robust way to solve this detection problem is to feed a sequence of audio fingerprints (such as MFCCs) to an RNN machine learning algorithm that was trained on a large wide range of rhythm tracks mixed with increasing levels of realistic background noise.

Feeding audio stream samples directly to a deeper CNN+RNN ML inference engine might work even better by detecting humanly resolvable beat details that audio fingerprinting misses, but that would be computationally far less efficient and would take a lot longer to train.