Video

Video is an electronic medium used for recording, copying, and displaying moving visual images. It can function with or without accompanying audio. The word itself comes from the Latin "video," which means "I see."

Today, video technology is essential for communication, entertainment, and education. It allows information to be shared across broadcast television, physical media, and internet platforms. While it began as a tool for live transmission, it has evolved into a complex digital system.

To understand how video works, one must look at the concept of frame rate. This is the number of still pictures shown per unit of time. To create the illusion of motion, a phenomenon called persistence of vision, a system needs at least 16 frames per second (fps). Modern professional cameras can reach 120 fps or higher. Different standards use different rates. For example, the NTSC standard uses 29.97 fps, while PAL and SECAM use 25 fps. Film is typically shot at 24 fps, which can make transferring it to video slightly complicated.

Video systems also use different methods to scan and display these frames. Progressive scan systems update every scan line in a frame in sequence. This provides the best spatial resolution for both still and moving parts. In contrast, interlaced scanning was invented to reduce flicker in older CRT displays. Interlacing divides a frame into two fields: an odd field and an even field. The device displays these fields one after another. This effectively doubles the perceived frame rate without requiring more bandwidth. NTSC, PAL, and SECAM are all interlaced formats.

Historically, video technology moved from mechanical systems to analog electronic signals. Early mechanical scanners, like the Nipkow disk, were patented in 1884. These were eventually replaced by cathode-ray tube (CRT) systems. In these systems, an electron beam scans a photoconductive plate to create a voltage signal. This signal represents the brightness of the image. A major breakthrough occurred in 1951 when Charles Ginsburg led an Ampex team to develop a video tape recorder (VTR). This device wrote electrical signals onto magnetic tape.

In 1956, these recorders cost about US$50,000. By 1971, Sony brought videocassette recorders (VCRs) to the consumer market.

Digital video has largely replaced analog video because it offers higher quality at lower costs. The introduction of the DVD in 1997 and Blu-ray in 2006 led to a decline in videotape use. Digital technology allows for efficient compression and storage. This means even smartphones can capture and edit video. Digital broadcasting is also making analog video a legacy technology. In Hollywood, the shift is massive. Since 2013, the use of digital cameras has surpassed the use of film cameras.

Visual presentation is also defined by the aspect ratio. This is the proportional relationship between a screen's width and height. Traditional television uses a 4:3 ratio. High-definition televisions use a wider 16:9 ratio.

The way pixels are shaped can also change. While computer pixels are usually square, digital video often uses non-square pixels. Interestingly, mobile phone use has changed how we view video. In 2015, vertical video viewing grew to 29% of all viewing. Vertical ads are actually watched in their entirety nine times more often than landscape ads.

Color and data management are also vital to video quality. Systems use different color models, such as YUV for PAL or YCbCr for digital video. To save data, engineers use chroma subsampling. This process reduces the amount of color data while keeping the brightness data (luminance) intact. This works because the human eye is less sensitive to color detail than brightness.

To manage large file sizes, digital video uses compression. This involves reducing spatial redundancy within a frame and temporal redundancy between frames. Common standards include MPEG-2 for DVDs and MPEG-4 for the internet.

Finally, video can be expanded into three dimensions through stereoscopy. This creates a sense of depth for the viewer. One method uses two channels, one for each eye, often paired with polarized filters. Another method is anaglyph 3D, which uses red and cyan color-coded layers. A third method uses LCD shutter glasses that alternate which eye sees which frame. This is common in virtual reality. These various technologies all work together to shape how we experience moving images.