On TikTok, pop stars — Halsey, FKA Twigs, and Florence Welch among them — have been complaining a lot lately about their labels forcing them to make TikToks. As people spent the early part of the pandemic staring at their phones instead of flocking to concerts, the short-form-video social-media platform upended music discovery. In many cases, it gave unknown musicians a pathway to enormous audiences and allowed them to burst into the mainstream on the backs of their TikTok hits. It’s a story as old as the music industry itself: No-name musician gets big overnight and lands a record deal. But until recently, it’s been hard to say just how big and how overnight, so Estelle Caswell from Vox and Matt Daniels from The Pudding spent seven months manually compiling and interrogating the data of who went viral, who got signed, and whose careers dropped off. Their resulting short documentary, We Tracked What Happens After TikTok Songs Go Viral, is a definitive dive into the 2020 class of...