video on the second, third and fourth screen

I periodically hear some director or pundit talk about how terrible it is to watch a movie on a laptop or mobile phone. And at face value, it makes sense:

That phone is so tiny! Why would anyone watch a movie on that? And the laptop is pretty marginal. Until you actually take into account reality, and users and math.

People automatically adjust for what we (possibly incorrectly) call angular resolution. Entirely aside from phones being hand-held, they get moved to the right distance to see things correctly. Broadly speaking, video display ends up occupying the same field of view regardless of the device size. This is why people actually do watch video on phones, and will continue to do so.