Digital video encoding
The first forms of digital video encoding began in the 1970s with uncompressed video with pulse code modulation (PCM), which requires high bit rates of 45 to 140 Mbit / s for standard definition of content (SD) .
Practical digital video coding was finally made possible by Discrete Cosine Transform (DCT), a form of lossy compression. DCT compression was first proposed by Nasir Ahmed in 1972 and later developed by Ahmed with T. Natarajan and K.R. Rao at the University of Texas in 1973. DCT later became the standard for digital video compression since the late 1980s. The first digital video coding standard was H.120, created by CCITT (now ITU-T) in 1984.
H.120 was impractical due to poor performance. H.120 relied on differential pulse code modulation (DPCM), a lossless compression algorithm that was ineffective for video encoding. In the late 1980s, several companies began experimenting with DCT, a much more efficient form of compression for video encoding. The CCITT received 14 proposals for DCT-based video compression formats, as opposed to a proposal based on vector quantization (VQ) compression. H.261 standard was developed based on DCT compression. H.261 was the first practical video coding standard. Since H.261, DCT compression has been adopted by all subsequent major video coding standards. MPEG-1, developed by a group of experts in Cinematography (MPEG), followed in 1991, was designed to compress the video quality of VHS. It was replaced in 1994 by MPEG-2 / H.262, which became the standard video format for DVD and SD digital television. It was followed by MPEG-4 / H.263 in 1999, followed by H.264 / MPEG-4 AVC in 2003, which has become the most widely used video coding standard.
Digital video production
From the late 1970s to the early 1980s, various types of video production equipment were introduced, the inner workings of which were digital. These include time base correctors (TBC) and digital video effects units (DVE). They worked by taking a standard analog composite video input and digitizing it internally. This made it easier to fix or enhance the video signal, as in the case of TBC, or manipulate and add effects to the video, in the case of a DVE device. The digitized and processed video information was converted back to standard analog video for output. Later, in the 1970s, professional video transmission equipment manufacturers such as Bosch (through its Fernseh division) and Ampex developed prototypes of digital video recorders (VTRs) in their research labs.
The Bosch machine used a modified 1-inch Type B videotape conveyor and recorded an older version of the CCIR 601 digital video. The Ampex digital video recorder prototype used a modified 2-inch quadruplex video recorder (Ampex AVR-3), but equipped with special digital video electronics and a special octaplex-type octaplex wheel (conventional quad-core 2-core analog machines). Inches only use 4 Like a standard 2-inch ATV, the sound on the Ampex digital machine prototype, dubbed by the developers as Annie still recorded analog audio as linear tracks on tape, none of these machines were sold on the market.
Digital video was first introduced commercially in 1986 in the Sony D1 format, which recorded uncompressed standard definition component video in digital form. Component video required 3 cables, and most TV devices were connected to NTSC or PAL composite video with a single cable. Due to this incompatibility and also the cost of the recorder, the D1 has been used primarily by large television networks and other video studios that support component video.
In 1988, Sony and Ampex jointly developed and released the D2 digital videocassette format, which digitally recorded uncompressed video in the ITU-601 format, just like the D1. But the D2 had a big difference in composite video encoding from the NTSC standard, requiring only a single cable composite video connection to and from the D2 VCR, making it ideal for most television venues. at that moment. The D2 format was successful in the broadcasting industry in the late 1980s and 1990s.
