B frame (bidirectional frame), a video compression method used by the MPEG standard. In a motion sequence, individual frames of pictures are grouped together (group of pictures, or GOP) and played back so that the viewer registers the video’s spatial motion. As the name suggests, B frames can use both previous and forward frames for data reference to get the highest amount of data compression. B frames contain only the data that have changed from the preceding frame or are different from the data in the very next frame.