When television screens went digital, they became subject to technology improvements. Better picture quality came from increasing the number of pixels on a screen. The first digital screen supported Standard Definition television with 640 pixels across the screen and 480 pixels down. Painting every other pixel with a 16-bit color 30 times a second (the minimum with interlaced scanning) would require a data rate around 75 mbps (480 x 640 x 16 x 30 divided by 2) a figure possible now but unthinkable in the late 1980s when digital television was making its debut. So engineers figured out ways of compressing the digital signal, with some loss of fidelity, to around 1.5 mbps. You have no doubt seen the effects in screen tiling and distortions when people move too fast. The actual rate for any given video varies a small amount depending upon things like how fast the images changed and how fast the colors changed.
But that was a small television with interlaced scanning. Television screens got bigger and interlaced scanning gave way in many cases to progressive scanning where every pixel was painted for every scan, at a rate of 60 times a second, not 30. Compression got better as well (otherwise we would not have the better televisions). The next generation was High Definition TV (HDTV), with a screen measured by 1920 pixels across and 1200 pixels down. In RAW form and 16-bit color this screen size required a data rate of 2.2 gigabits per second (gbps). Compression miraculously reduced the data rate now in use to around 7 mbps, with some infirmities in quality but a data rate sustainable over cable television networks.
Next in the history of things to come was HD video over cellular networks and wired data networks that delivered video Over The Top (OTT), that is, over the Internet rather than a cable television network. Don’t let small screens fool you. The iPhone X has a pixel space that measures 1125 x 2436. Furthermore, colors have wandered up to 32 bits from 16 for some video experiences. Painting every pixel on an iPhone X at 32 bits 60 times a second for progressive scanning requires 5.26 gigabits per second. Radical compression can get that under 10 mbps with loss of fidelity, but a key driver for upgrading speeds in cell phone networks is cell phone video. Seventy-five percent of Internet traffic now is video.
Clearly, HD television is not going to work over old DSL networks limited by line distance to a maximum of 8 mbps (16 if using two telephone lines), with the average coming in below 4 mbps. But it will work over cable television data channels at 25 mbps or more. Ironically then, OTT television, the bane of cable television broadcast channels as people “cut the cord,” comes to us mostly through cable television Internet subscriptions. Hulu, Amazon Video, and other television video services require cable television networks to have a chance in the market.
But the market is not standing still. As screen sizes increased, many now at 60 inches or more, manufacturers figured out ways of getting more pixels per inch on the screen. The next size, designated as Ultra High Definition Television (UHD) provides 3840 pixels across and 2160 pixels down. The horizontal pixel size has given the name 4K to these screens. The screen dazzles for sports and fast-paced video games. Data rates to paint these screens now rise to 30 mbps as a kind of nominal figure with the usual variations around the number depending upon the effects of compression. 4K is the future of television; 25% of all televisions sold today have 4K screens, and the iPhone X claims 4K quality in a screen five-inches high.
Cable television networks are now stuck. CATV networks devote a fixed amount of bandwidth to television channels. They use modems to digitize this bandwidth and send digital televisions signals down this bandwidth. Its total capacity is suitable to the present arrangement of Standard and HD television, but is at its limit. So they have no capacity to send broadcast UHD (4K) material. They are similarly limited on video-on-demand, that bandwidth fighting with increased demand for Internet channels. According to reports cable television companies plan to upgrade their networks to eliminate the bandwidth devoted to sending all 220 channels to everyone, creating what amounts to a full video-on-demand system, hoping to free up bandwidth for non-broadcast television services. But this is extremely expensive and as far as we know has not even begun anywhere (it changes many things in their system).
We are not through. Television companies are also developing screens with pixel spaces of 7680 x 4320, called 8K in the market vernacular. This screen will require 90 mbps per video experience. It does not take a lot of analysis to show that widespread use of 8K screens will require fiber optic networks.