Цифровое видео: технологии и развитие

Digital electronic representation of moving visual images
digital techniques applied to video

Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises a series of digital images displayed in rapid succession, usually at 24, 30, or 60 frames per second. Digital video has many advantages such as easy copying, multicasting, sharing and storage. Digital video was first introduced commercially in 1986 with the Sony D1 format, which recorded an uncompressed standard definition component video signal in digital form. In addition to uncompressed formats, popular compressed digital video formats today include MPEG 2, H.264 and AV1. Modern interconnect standards used for playback of digital video include HDMI, DisplayPort, Digital Visual Interface (DVI) and serial digital interface (SDI). Digital video can be copied and reproduced with no degradation in quality. In contrast, when analog sources are copied, they experience generation loss. Digital video can be stored on digital media such as Blu ray Disc, on computer data storage, or streamed over the Internet to end users who watch content on a personal computer or mobile device screen or a digital smart TV. Today, digital video content such as TV shows and movies also includes a digital audio soundtrack.

The basis for digital video cameras is metal–oxide–semiconductor (MOS) image sensors. The first practical semiconductor image sensor was the charge coupled device (CCD), invented in 1969 by Willard S. Boyle, who won a Nobel Prize for his work in physics. Following the commercialization of CCD sensors during the late 1970s to early 1980s, the entertainment industry slowly began transitioning to digital imaging and digital video from analog video over the next two decades. The CCD was followed by the CMOS active pixel sensor (CMOS sensor), developed in the 1990s. Major films shot on digital video overtook those shot on film in 2013. Since 2016 over 90% of major films were shot on digital video. as of 2017, 92% of films are shot on digital. Only 24 major films released in 2018 were shot on 35mm. Today, cameras from companies like Sony, Panasonic, JVC and Canon offer a variety of choices for shooting high definition video. At the high end of the market, there has been an emergence of cameras aimed specifically at the digital cinema market. These cameras from Sony, Vision Research, Arri, Blackmagic Design, Panavision, Grass Valley and Red offer resolution and dynamic range that exceeds that of traditional video cameras, which are designed for the limited needs of broadcast television.

In the 1970s, pulse code modulation (PCM) induced the birth of digital video coding, demanding high bit rates of 45 140 Mbit/s for standard definition (SD) content. By the 1980s, the discrete cosine transform (DCT) became the standard for digital video compression. The first digital video coding standard was H.120, created by the (International Telegraph and Telephone Consultative Committee) or CCITT (now ITU T) in 1984. H.120 was not practical due to weak performance. H.120 was based on differential pulse code modulation (DPCM), a compression algorithm that was inefficient for video coding. During the late 1980s, a number of companies began experimenting with DCT, a much more efficient form of compression for video coding. The CCITT received 14 proposals for DCT based video compression formats, in contrast to a single proposal based on vector quantization (VQ) compression. The H.261 standard was developed based on DCT compression, becoming first practical video coding standard. The current generation video coding format is HEVC (H.265), introduced in 2013. While AVC uses the integer DCT with 4x4 and 8x8 block sizes, HEVC uses integer DCT and DST transforms with varied block sizes between 4x4 and 32x32. HEVC is heavily patented, with the majority of patents belonging to Samsung Electronics, GE, NTT and JVC Kenwood. It is currently being challenged by the aiming to be freely licensed AV1 format. as of 2019, AVC is by far the most commonly used format for the recording, compression and distribution of video content, used by 91% of video developers, followed by HEVC which is used by 43% of developers.

Starting in the late 1970s to the early 1980s, video production equipment that was digital in its internal workings was introduced. These included time base correctors (TBC) and digital video effects (DVE) units. They operated by taking a standard analog composite video input and digitizing it internally. This made it easier to either correct or enhance the video signal, as in the case of a TBC, or to manipulate and add effects to the video, in the case of a DVE unit. The digitized and processed video information was then converted back to standard analog video for output. Later on in the 1970s, manufacturers of professional video broadcast equipment, such as Bosch (through their Fernseh division) and Ampex developed prototype digital videotape recorders (VTR) in their research and development labs. Bosch's machine used a modified 1 inch type B videotape transport and recorded an early form of CCIR 601 digital video. Ampex's prototype digital video recorder used a modified 2 inch quadruplex videotape VTR (an Ampex AVR 3) fitted with custom digital video electronics and a special octaplex 8 head headwheel (regular analog 2" quad machines only used 4 heads). Like standard 2" quad, the audio on the Ampex prototype digital machine, nicknamed Annie by its developers, still recorded the audio in analog as linear tracks on the tape. None of these machines from these manufacturers were ever marketed commercially. Digital video was first introduced commercially in 1986 with the Sony D1 format, which recorded an uncompressed standard definition component video signal in digital form. Component video connections required 3 cables, but most television facilities were wired for composite NTSC or PAL video using one cable. Due to this incompatibility the cost of the recorder, D1 was used primarily by large television networks and other component video capable video studios. In 1988, Sony and Ampex co developed and released the D2 digital videocassette format, which recorded video digitally without compression in ITU 601 format, much like D1. In comparison, D2 had the major difference of encoding the video in composite form to the NTSC standard, thereby only requiring single cable composite video connections to and from a D2 VCR. This made it a perfect fit for the majority of television facilities at the time. D2 was a successful format in the television broadcast industry throughout the late '80s and the '90s. D2 was also widely used in that era as the master tape format for mastering laserdiscs. D1 & D2 would eventually be replaced by cheaper systems using video compression, most notably Sony's Digital Betacam, that were introduced into the network's television studios. Other examples of digital video formats utilizing compression were Ampex's DCT (the first to employ such when introduced in 1992), the industry standard DV and MiniDV and its professional variations, Sony's DVCAM and Panasonic's DVCPRO, and Betacam SX, a lower cost variant of Digital Betacam using MPEG 2 compression. One of the first digital video products to run on personal computers was PACo: The PICS Animation Compiler from The Company of Science & Art in Providence, RI. It was developed starting in 1990 and first shipped in May 1991. PACo could stream unlimited length video with synchronized sound from a single file (with the CAV file extension) on CD ROM. Creation required a Mac, and playback was possible on Macs, PCs, and Sun SPARCstations. QuickTime, Apple Computer's multimedia framework, was released in June 1991. Audio Video Interleave from Microsoft followed in 1992. Initial consumer level content creation tools were crude, requiring an analog video source to be digitized to a computer readable format. While low quality at first, consumer digital video increased rapidly in quality, first with the introduction of playback standards such as MPEG 1 and MPEG 2 (adopted for use in television transmission and DVD media), and the introduction of the DV tape format allowing recordings in the format to be transferred directly to digital video files using a FireWire port on an editing computer. This simplified the process, allowing non linear editing systems (NLE) to be deployed cheaply and widely on desktop computers with no external playback or recording equipment needed. The widespread adoption of digital video and accompanying compression formats has reduced the bandwidth needed for a high definition video signal (with HDV and AVCHD, as well as several professional formats such as XDCAM, all using less bandwidth than a standard definition analog signal). These savings have increased the number of channels available on cable television and direct broadcast satellite systems, created opportunities for spectrum reallocation of terrestrial television broadcast frequencies, and made tapeless camcorders based on flash memory possible, among other innovations and efficiencies.

Culturally, digital video has allowed video and film to become widely available and popular, beneficial to entertainment, education, and research. Digital video is increasingly common in schools, with students and teachers taking an interest in learning how to use it in relevant ways. Digital video also has healthcare applications, allowing doctors to track infant heart rates and oxygen levels. In addition, the switch from analog to digital video impacted media in various ways, such as in how businesses use cameras for surveillance. Closed circuit television (CCTV) switched to using digital video recorders (DVR), presenting the issue of how to store recordings for evidence collection. Today, digital video is able to be compressed in order to save storage space.

Digital television (DTV) is the production and transmission of digital video from networks to consumers. This technique uses digital encoding instead of analog signals used prior to the 1950s. As compared to analog methods, DTV is faster and provides more capabilities and options for data to be transmitted and shared. Digital television's roots are tied to the availability of inexpensive, high performance computers. It was not until the 1990s that digital TV became a real possibility. Digital television was previously not practically feasible due to the impractically high bandwidth requirements of uncompressed video, requiring around 200Mbit/s for a standard definition television (SDTV) signal, and over 1Gbit/s for high definition television (HDTV).