 B-frame data. Again since the actual and estimated values are not exactly equal, the difference between the two is encoded and transmitted as B-frame. The calculation relationship between of I-, P- and B-frames is illustrated in Figure 5.24. Broadband Telecommunications Technologies and Management Figure 5.24 Relationship between I-, P- and B-frames Table 5.7 Common MPEG video compression standards and applications Codec Standard Applications MPEG-1 H.261 Video CD DAB MPEG-2 H.262 DVD, Blu-Ray DVD DVB Blu-Ray DVD Video streaming (YouTube, Vimeo, etc.) MPEG-4 H.264 Video telephony (e.g. FaceTime) HDTV broadcasting XAVC (4K) MPEG-H H.265 High efficiency video coding 8K ultra high definition TV A number of video coding standards have been developed since 1988 within the MPEG group under the auspices of ITU [27]. These standards have been instrumental in facilitating video conferencing, digital TV, video telephony and video streaming application. A list of the main standards and their applications are shown in Table 5.7. Although natural signals are continuous and analogue, they may be represented in a discrete, practical manner to be perceived 'natural' by a human observer. Discrete or digital represen- tation of signals allows for better preservation and processing of information and enables the realisation of theoretical telecommunications capacity limits. Furthermore, considering our limited perceptual capability, digital representation and processing enables an efficient but acceptable representation of analogue signals. These are some of the principles behind the recent digital transformation of our society. Review Questions 1. Why do you think sampling rate is known as the Nyquist rate despite contributions from many scientists prior to his formulation? 2. What is sampling rate and how is it calculated? 3. What is quantisation level and what factors are considered in its determination? 4. How does digital transmission compare with analogue? Why has digital become popular? 5. Why do errors occur in digital com