I’ve devoured, by now, countless hours of B-roll. I’ve watched shoppers peruse CDs at the long-shuttered Tower Records on Newbury Street in the ’90s, transporting me back to Saturdays in high school when my friends and I browsed the rap and hip-hop racks for hours. Cars as big as boats — station wagons, sedans and vans like my parents drove — roll over the Tobin Bridge in 1979; drivers reach out their arms to pass cash and coins to toll attendants. I’ve watched ice skaters gliding over the frozen Charles River in the late ’70s and hairsprayed teenagers in leather and oversize sweaters smoking cigarettes outside their high school in the ’80s.