Actually that is incorrect... here is a lesson on B-roll film and where A-roll film plays into it. (and yes it does mean Beta)
B-roll or B roll is the alternate footage shot to intercut with the primary shots used in a program. It is frequently used for cutaway shots. Ideally these should fit with the continuity of the base track. It is video that enhances or tells the story. It was originally used to cover a jump cut in editing. It is now more commonly used to add dimension to a story. For example, if a person is talking about a new school, the B-roll will include video of the new school. It can be stock footage acquired for miscellaneous needs. B roll is the secondary or "safety" footage for a film. In order to string together two interview clips that were not shot consecutively, an editor will cut away from A roll to B roll, while the audio from the A roll shot plays under. Then when the editor cuts back to the second A roll shot, it appears as if the concepts were always married together.
This technique of using the cutaway is common to hide zooms in documentary films: the visuals may cut away to B roll footage of what the person is talking about while the A camera zooms in, then cut back after the zoom is complete. The cutaway to B roll footage can also be used to hide verbal or physical tics that the editor and/or director finds distracting: with the audio separate from the video, the filmmakers are free to excise "uh"s, sniffs, coughs, and so forth. In fiction film, the technique can be used to indicate simultaneous action or flashbacks, usually increasing tension or revealing information.
"B roll" also refers to footage provided free of charge to broadcast news organizations as a means of gaining free publicity. For example, an auto maker might shoot a video of its assembly line, hoping that segments will be used in stories about the new model year.
