Read all files from all the folders

I am using Windows, Jupyter Notebook, OpenCV, Mediapipe, Tensorflow.

Hello. I have a video Dataset with 100 action folders and each folder has 100 videos(.avi). Frames Per Second is 25. I want to read all the videos in all the action folders to collect the keypoints.

I just want help with the code reading all the videos from all the folders using for loop or anything. And is there anyway to check if that code indeed read all the videos from all the folders?

Please help. Thank You.