“Nowadays, YouTube is almost alarmingly professional. It has millions of channels devoted to personalities and products, which are often aggregated into “verticals” containing similar content. The most popular videos are filmed by teen-agers and twentysomethings who use Red Epic cameras and three-point lighting to shoot themselves. And the platform’s stars behave in ways that are contingent upon a camera. For instance, they act. One of YouTube’s most visible shows—currently featured in magazine and subway-car ads everywhere—is an action series called “Video Game High School” that would be right at home on MTV.”