How to keep viewers engaged in an online video

Your 4 tips are probably true for that particular type of short "testimonial" video but not necessarily true for longer videos.

For me it comes down to context, content and expectations. I expect a short testimonial video on your landing page that gets to the point, not a 4 minute drawn out circle jerk. If I see a runtime of 4 minutes on a testimonial video, I probably won't even click play to begin with. A Mixergy video on the other hand is something I expect to be long and not necessarily pack a punch right up front.

Do you find the viewing data from longer videos to be consistent with your 4 suggestions?

Along the lines of cutting the videos short. Cut them down shorter than you feel is warranted. These videos should be product teasers.