Definition:
Every edit has two layers. The A-Roll carries the story. The B-Roll is everything else: the supplementary footage that supports, illustrates, and gives context to what the primary material is doing. Without it, most cuts would collapse into a static talking head with nowhere to go.
What It Means in Movies:
B-Roll is what keeps a cut breathing. In a documentary, when the subject talks about a city they grew up in, the shots of that city's streets are B-Roll. In a narrative film, the cutaway to a clock on the wall, a hand reaching for a door handle, a face watching from across the room: all B-Roll. It is the visual layer the editor reaches for when the A-Roll needs support, rhythm, or a moment to let the audience catch up.
Why It Matters:
Editors talk about B-Roll the way builders talk about materials. Too little and you cannot do the job properly. The right B-Roll does more than cover a cut. It shapes meaning. The choice of what B-Roll to shoot and how to cut it against the A-Roll is where a significant portion of documentary storytelling actually happens.
Example:
In a streaming documentary about the music industry, an artist describes performing live in an interview. The concert footage cut over their words, the crowd shots, the close-ups of instruments, and the stage lighting catching the back of their heads: that is all B-Roll. It brings the conversation to life in a way the interview alone never could.