Wed, 17 Apr 2002 08:30:44 -0700 (PDT)
I hadn't heard of this expression either, but a "b-roll" appears to
be a simultaneously shot film clip which allows the news editor to switch
clips in the main "a-roll" without interrupting the audio. It was
necessitated by fast-paced news production, pre-video.
Sorry for the poor summary, but a clearer explanation is at