I was filming a series of tutorials over the weekend and one of the models we worked with asked at one stage: "Guys, you keep talking about 'B-roll'. What is B-roll?" I gave her some convoluted answer that made a distinction between your main footage and secondary footage or something like that. But this morning I came across this great video on News Shooter that would've explained the notion much more succinctly.
Slavik Boyechko from Alaska Public Media shoots a short documentary every week for PBS Digital Studios and came up with this short tutorial explaining the importance of good B-roll and highlighting a few useful techniques. Great stuff if you're just starting out as a documentary maker.
In Slavik's words, "once you start editing the video, you'll need to cover the cuts - and that's where B-roll comes in". What a brilliant definition.
Where Slavik and I differ - but that's purely personal preference - is the sequence of events. He prefers to shoot B-roll before the main interview. But quite often, it seems, he simply doesn't have a choice. I prefer to shoot the interview first, if possible, as most of the time the interview will simply give you ideas for B-roll.
Here's Slavik's tutorial: