Short for bi-directional frame, or bi-directional predictive frame, a video compression method used by the MPEG standard. In a motion sequence, individual frames of pictures are grouped together (called a group of pictures, or GOP) and played back so that the viewer registers the video��s spatial motion. As the name suggests, B-frames rely on the frames preceding and following them. B-frames contain only the data that have changed from the preceding frame or are different from the data in the very next frame.
P-frames and B-frames are also referred to as delta frames.