B roll

In film and television production, B-roll (B roll, or Broll) is supplemental or alternative footage intercut with the main shot. In fiction film, it is a technique used to indicate simultaneous action or flashbacks.

The term B-roll originates from the method of 16 mm film production from an original camera negative. Frames of workprint and of original negative are matched exactly through the use of edge numbers that appeared on each frame of original and work print. But the original was not strung together in a simple linear fashion as was the work print. Instead, the original was edited in a "checkerboard" pattern, with each shot synchronized to an equal length of opaque leader on a second or "B" roll.

"A and B" rolls functioned equally to make blind splices, fades, and dissolves possible. Each roll was printed separately onto a single roll of raw stock to produce projection prints. The process is described in the 1982 edition of the "Recommended Procedures" of the Association of Cinema and Video Laboratories, and in the 1962 text Film and Its Techniques.

Then the term B-roll was adopted for the older form of linear-based editing and the common naming conventions used by most television production facilities. Traditionally, the tape decks in an edit suite were labelled by letter, with the 'A' deck being the one containing the main tape upon which the main action material was shot. The 'B' deck was used to run tapes that held additional, typically soundless, footage such as establishing shots, cutaway shots, and any other supporting footage. As linear editing systems were unable to dissolve between clips on the same tape, an edit decision list (EDL) was used to mark clips as "a-roll" and "b-roll" to indicate source machines.

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