dcast analogue TV uses 6-8 MHz of bandwidth. Using PCM digital encoding with a 224 quantisation range will lead to: 8*2*24 = 384 Mbps. A DVD can store 4.5 gigabytes of data, and at this rate can provide storage for 94 S of digital video. Even transmission of individual image frames is imprac- tical. If an image is encoded with 500 kilobytes, a 30 frames/s video requires 15 Mbps transmission rate. Since consecutive image frames are highly correlated, video encoding needs to decorre- late these images to reduce the total number of required bits. The principle is therefore similar to differential coding described in relation to voice, audio and image coding: once an image has been coded, subsequent images can be coded by calculating their difference from the initial image. All these standards encode video by producing three types of frames through prediction and differential encoding based on the DCT technology and temporal (inter-frame) differential coding. Three kinds of frames are specified: intra-coded frames (I-frames), predictive-coded frames (P-frames), and bi-directionally predictive-coded frames (B-frames). I-frames are in effect JPEG files using the DCT technology. I-frame data are independent of previous or following frames. P-frames are temporally several frames after an I-frame and are calculated through a predictive differential process: the data for the P-frame is calculated by extrapolating the I-frame data. Since the extrapolation is not perfectly accurate, the difference between the actual value and the extrapolated value is calculated, encoded and transmitted as the value of the P-frame. As the difference is generally of a smaller size it provides more compression as P-frames take advantage of I-frame information. In practice several P-frames are extrapolated and differentially calculated. B-frames represent the information for the frames between I- and P-frames. Their data is cal- culated based on prediction and differential coding. An interpolation between I- and P-frames is made to estimate the