Put simply, B-roll is the extra footage you need to shoot to support or augment what your subjects (or you) are talking about in the “A-roll”. The idea is that you will be shooting primary (A-roll) footage of interviews, a laboratory method, or a field site. However, you will need additional material to illustrate aspects of this primary footage. This is the B-roll. For you digital generation folks, a “roll” refers to the old type of photographic film that was wound around a spool. The term has an interesting history, which you can read about here.
I routinely shoot a variety of secondary footage when I go out to capture my primary footage. These include both video and still images as well as sound effects that might come in handy during editing. I always try to get footage of traveling to and from a field site, for example, to use during the title sequence and the credit sequence at the end of the video. Sometimes these clips are shot from a car, a boat, or a plane, and I try to frame the shot so that there is space for the text that I will insert during editing. Here’s a clip that illustrates what I mean:
I shot that footage during the airboat ride to and from the field site where I did interviews and captured other primary footage. I used those clips for both title and end sequence, which worked out well, I think. The entire video can be seen here.
I usually spend some time at the location of the shoot filming various closeups of plants and animals as well as landscapes, waves breaking on the shoreline, rain, vehicles moving past, people, buildings, shadows, or whatever characterizes the location. I additionally shoot still images, especially closeups of flowers, insects, or other items that I can use in a montage of scenes. Once I’ve completed the interview, then I walk around and shoot video or still images of whatever the interview subject has mentioned. Then, I can insert those images during editing so that a long interview is not just of a talking head, but has interesting images or clips interspersed with the interview footage. Here is an example from the same video as above:
If you are doing a video of a laboratory method, you will want to get various shots of equipment from different angles as well as people going about their work. You will probably work out a lot of these shots beforehand, but it’s always a good idea to shoot extra scenes and even things that are not central to the subject. These types of footage may turn out to be useful during the introduction to the video or as a transition between interviews.
I also capture sound effects that might be useful for a montage of still images, for example: sounds of dripping water, waves breaking, birds or crickets chirping, a crackling fire, lions roaring (got this sound effect on a trip to Botswana).
During my work as a researcher, I got into the habit of setting aside time during a field trip to take photographs for later use in presentations and journal articles. I would first make a list of items that I needed a photo of, and then go out and search for them. Sometimes, I would spend an entire day (during a long field trip) just shooting photos. So it was second nature for me to apply the same practice to shooting video.
Get into the habit of taking your camcorder or camera with you and shoot whatever you are doing–in the lab or in the field. Believe me, it will be worth the time and effort when you sit down to edit your video.