Designing a ConvNet to facilitate game playing
I've recently started using OpenCV's python implementation, and I found some good OpenCV tutorials on this website: http://www.pyimagesearch.com/ that I really liked. OpenCV allows you to do Haar Cascades for fast facial recognition (by default it doesn't use a convoluted neural network but an optimized implementation of Ada Boosting that evaluates frames in stages for faster processing). OpenCV converts each frame into a multidimensional numpy tensor/matrix that you can then feed into into your ML algorithm (e.g., in TensorFlow or some other library), although I think most people just use the built-in OpenCV face classifiers. In any case, I believe OpenCV can process up to 70 frames per second, so it should be fast enough for you. 

The original paper that invented Haar Cascades:
https://www.cs.cmu.edu/~efros/courses/LBMV07/Papers/viola-cvpr-01.pdf

The OpenCV documentation that further explains Haar Cascades:
http://docs.opencv.org/3.1.0/d7/d8b/tutorial_py_face_detection.html#gsc.tab=0