How to convert two channel audio into one channel audio
To convert any stereo audio to mono, what I have always seen is the following:
For each pair of left and right samples:

Add the values of the samples together in a way that will not overflow
Divide the resulting value by two
Use this resulting value as the sample in the mono track -  make sure to round it properly if you are converting it to an integer value from a floating point value
I am playing around with some audio processing in python.  Right now I have the audio as a 2x(Large Number) numpy array.  I want to combine the channels since I only want to try some simple stuff.  I am just unsure how I should do this mathematically.  At first I thought this is kind of like converting an RGB image to gray-scale where you would average each of the color channels to create a gray pixel.  Then I thought that maybe I should add them due to the superposition principal of waves (then again average is just adding and dividing by two.)  Does anyone know the best way to do this?