(modulation), as seen in Figure 3.4. K = R1/R2 is the data compres- sion ratio. M = R2/B in bits/Hz is a measure of the channel coder efficiency. We are interested in the cascaded effect of analogue-to-digital conversion, compression, and modulation. We measure overall performance by the ratio of output to input bandwidth, which we term the bandwidth expansion ratio, E. Therefore: (3.1) Video Compression Standards Considerable research in still-picture and video coding has resulted in a set of standards that can reduce the bitrate requirements by orders of magnitude while still maintaining subjective quality. Commonly used video compression standards are MPEG-1, MPEG-2, MPEG-4, H.261, H.263/263+, H.264, and H.261. Still-Image B bits Still-Image B bits Compression Video R1 bits/s Technique Video R2 bits/s Fig. 3.2 Finding the compression ratio. Compression Overview Bits/s SHDTV 3D TV Broadcast Video- conferencing, Video on Demand, Surveillance Internet Video, Fax, Still Images Fig. 3.3 Bitrates for various applications with and without compression. Analogue Source Coder Channel Coder Digital Source N Bits/ (Data Channel (Modulator) Signal sample Compressor) Signal Bandwidth = W Bandwidth = B Uncompressed Compressed Digital Signal Bitrate R1 = 2 WN Bitrate R2 = R/K Fig. 3.4 Sampling, compression, and modulation. MPEG, the Moving Picture Experts Group, standardized MPEG-1 in 1992. The system was designed for VHS-quality video and at 1.2 Mbit/s could hold 75 minutes on a 640- Mbyte compact disk. It had SIF-size images (352 X 288) at 25 Hz and offered editing facilities along with the first example of software coding. It was also suitable for streaming over IP. It used I, B, and P pictures, half-pixel motion estimation, and a slice structure to limit the effects of error propagation. It did not support interlaced video and was effectively super- seded by MPEG-2. The MPEG-2 standard was published by the ISO/IEC in 1994 and was designed to provide high-quality video encoding suitable for transmission over computer netwo