subsequent ones. In a motion sequence each pixel can have a distinct displacement from one frame to the next. From a practical point of view, however, adjacent pixels tend to have the same displacement. Motion compensation uses motion vectors and rate- of-change analysis to exploit inter-frame similarities. An image is divided into rectangular blocks and a single displacement vector to describe the movement of all pixels within the block. Motion JPEG A compression technique that applies JPEG compression to each frame of a video clip. motion vectors In the H.261 Recommendation this optional calculation can be included in a macroblock. Motion vector data consists of one code word for the horizontal information followed by a code word for the vertical information. The code words can be of variable length and are specified in the H.261 standard. Performing motion vector calculations Glossary of Terms places more demand on a processor and many systems do not include this capability, which is optional for the source coder. If a source encoder performs the motion compensation processing, the H.261 Recommendation requires that the decoder use it during decompression. motion video capture board A device designed to capture, digitize and compress multiple frames of video for storage on magnetic or optical storage media. Motion Picture Experts Group JTC1/SC29/WG11 standard that specifies a variable rate compression algorithm that can be used to compress full-motion image sequences at low bit rates. MPEG is an international family of standards that are not used for videoconferencing, but are more generally used for video images stored on CD-ROM or video servers and retrieved in a computer or television application. MPEG compresses YUV SIF images. It uses the same DCT algorithm used in H.261 and H.263 but uses 16 by 16 pixel blocks for motion compensation. MPEG-1 Joint ISO/IEC recommendation known as "Coding of Moving Pictures and Associated Audio for Digital Storage Media at up to about 1.5 Mbps." MPEG-1 was completed in Oct