The term B-roll originates from the early days of film, when editors inserted supplemental footage, or B-roll, into the main footage, or A-roll, to hide visible lines where two pieces of film were joined. In modern film and video production, B-roll describes all of the footage that isn’t the main action.
This supplemental footage includes all of the shots that don’t include the principal subjects interacting with each other or talking into the camera. It can come from stock footage, archival footage or photos, and second unit crews whose whole job is to capture B-roll shots.
Though digital video has eliminated the problem of film splicing, makers of both scripted and unscripted video still use B-roll to establish scenes, smooth transitions, and cut out coughs or unwanted frames without throwing away a whole shot. “Even though it sounds like it’s secondary, B-roll is what creates the nuances of visual storytelling,” says director and cinematographer Hiroshi Hara.