Updated on 21/12/2015
Interesting brief post on the edX blog by Philip Guo about video usage, obtained from initial analyses of some edX maths and science courses. The chart below shows "median engagement times versus video length, aggregated over several million video watching sessions". What is not clear from the analysis is whether viewers of long videos may be watching them to completion in short segments. If they are, then the "up to six minutes" point is not so strong.