B-roll is any topical, but non-specific, material used to establish context or mood or to support the narrative contained in the main footage or dialogue. The phrase comes from the early days of film editing, when editors would have two rolls of actual film to work from. The A-roll would form the bulk of the final product, while the B-roll would be used to improve the timing and atmosphere of the A-roll.
We got that B-roll!
You’ve probably seen this in action; in a documentary about Silicon Valley, for example, you might hear interview dialogue continuing over shots of server farms in California, or generic footage of people using smartphones, or indeed, the interviewee themselves going about their daily business. Because early editors were working with film, the film itself had to be cut in order to splice in B-roll - thus we get terms such as ‘cut into’ and ‘intercut.’ Here’s a perfect example from The Act of Killing (2012).
Good B-roll tells its own story
While he’s speaking, the character’s interview audio is playing over B-roll which the crew have shot of him campaigning for parliament in his neighbourhood. This footage doesn’t form part of the main visual narrative of the film, but serves as an excellent illustration of how eager the character is to talk about extorting money from his would-be constituents. Without this B-roll, the interview segment at the end of the clip would be perfectly fine, but just not quite as interesting.
Since the move away from physical film, the use of the term A-roll has faded away, but B-roll is still in use. ‘B-roll’ is sometimes used interchangeably with ‘stock footage,’ but this isn’t entirely accurate. Stock footage is pre-filmed material of just about any subject you can think of. B-roll can be drawn from stock footage, but stock footage is not itself B-roll.
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