B-roll is the supplemental footage that provides greater flexibility when editing video. Think of the footage used to cut away from an interview or news report to help tell the story. That's B-roll. When filming something static, like an interview or a news anchor reporting on-location, having shots of the environment makes the end-product more interesting to watch.
The footage from which you cutaway with B-roll is, naturally, called A-roll. As Vimean Dave Dugdale says in this video, A-roll doesn't have to be an interview. Whatever you've filmed as your main subject can work as your A-roll footage. Check out his explanation of B-roll here:
B-roll is also referred to as "safety footage" — and for good reason! If you've got moments that work for audio but not video — perhaps something distracting in the background or a necessary jump-cut — B-roll can help save the project by covering up these edits.
Check out Jeanious's B-Roll from a document he worked on in Cape Town, South Africa. There's a wide assortment of slow pans, timelapses, and static shots:
Here are a few tips for shooting B-roll:
• The most important thing is to capture as much variety as possible! Cover your bases by filming a good selection of wide shots and closeups, and try out some interesting angles, such as below the subject, or maybe a bird's-eye view of an event.
• Don't be afraid to move! Using only static shots can slow down the pace of the video.
• It's better to shoot more than is needed — you don't want to be left without enough to edit.
• Don't forget to capture B-roll of the person you are interviewing. Switching from an interview to a voice-over with footage of the person going about their business can help connect your audience with your subject.
• Make sure to get some B-roll on location after the interview; there may have been details mentioned that will inspire footage. For example, if you're interviewing a mother and she mentions her children, get some shots of those kiddos in the backyard, or of their photos around the house. And remember, although the industry term is "B-roll," this all-important footage shouldn't be dismissed as "B-list." B-roll can be creative and beautiful, and truly helps to produce a more well-rounded, engaging final piece.