History

Starting in the late 1970s to the early 1980s, Several kinds of video producing equipment Digital That Were In Their internal workings Were Introduced, Such As time basis Correctors (TBC) ^[a] and digital video effects (DVE) units. ^[b] They operate by taking a standard analog composite video input and digitizing it internally. This makes it easier to improve 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), RCA , and Ampex Developed prototype digital videotape recorders (VTR) In Their research and development labs. Bosch’s machine used a modified 1 “Type B transport, and recorded an early form of CCIR 601 digital video Ampex’s digital video recorder prototype used a modified 2” QuadruplexVTR (an Ampex AVR-3), but equipped with digital video electronics, and a special “octaplex” 8-head headwheel (regular analog 2 “Quad machines only used 4 heads.) The audio on Ampex’s digital prototype machine, nicknamed by its developers as “Annie”, still recorded the audio in analog as linear tracks on the tape, like 2 “Quad. None of these machines have been marketed commercially, however.

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 instead of the high-band analog forms that had been commonplace until then. Due to icts expense, and the requirement of component video connections using 3 cables (Such As YPbPr or RGB component video) to and from a D1 VTR That MOST television facilities were not wired for (composite NTSC or PAL video using one cable Was the norm for most of them at that time), D1 was used mainly 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. But D2 had the major difference of encoding the video in composite form to the standard NTSC, thus requiring a single-cable composite video connections to and from a D2 VCR, making it a perfect fit for the majority of television facilities at the time. This made D2 quite a successful format in the television broadcast industry throughout the late ’80s and the’ 90s. D2 was also widely used in the master tape format for mastering laserdiscs (prior to D2, most laserdiscs were mastered using analog 1 “Type C videotape ).

D1 & D2 would likely be replaced by cheaper systems using video compression , most notably Sony’s Digital Betacam (still heavily used as an electronic production field (EFP) recording format by television producers) which were introduced into the network’s television studios . Other examples of digital video formats utilizing compression were Ampex’s DCT (the first to be used in 1992), the industry standard DV and MiniDV (and its professional variations, Sony’s DVCAM and Panasonic’s DVCPRO ), and Betacam SX , a cost variant of Digital Betacam using MPEG-2 compression.

PACo could be one of the first digital video products in PACO: The PICS Animation Compiler from The Company of Science & Art in Providence, RI, which was developed starting in 1990 and first shipped in May 1991. ^[1] 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; was possible on Macs, PCs and Sun Sparcstations.

QuickTime , Apple Computer’s architecture for time-based and streaming data formats appeared in June, 1991. 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 (adopté for use in television transmission and DVD media), And Then the introduction of the DVtape format allowing recordings in the format to be transferred to digital video files (containing the same video data recorded on the DV tape) on an editing and editing process, allowing non-linear editing systems (NLE) to be deployed Widely it cheaply and desktop computers with no external playback / recording equipment needed, save for the computer simply Requiring a FireWire Port to interface to the DV-Format VCR or camera. The widespread adoption of digital video has also been reported to have a high-definition video signal (with HDV and AVCHD , more commercial variants such as DVCPRO-HD, all using less bandwidth than a standard definition analog signal) and tapeless camcorders based on flash memory and often a variant of MPEG-4 .

Overview

Digital video included a series of orthogonal digital bitmap images displayed in rapid succession at a constant rate. In the context of these images are called frames . ^[2] We measure the rate at which frames are displayed for second (FPS) . Since every frame is an orthogonal bitmap digital image it includes a raster of pixels . If it has a width of W pixels and a height of H pixels we say that the frame size is W xH. Pixels have only one property, their color. The color of a pixel is represented by a fixed number of bits. The more bits of the subtle variations of colors can be reproduced. This is called the color depth (CD) of the video.

An example video can have a duration (T) of 1 hour (3600 sec ), a frame size of 640×480 (WxH) at a color depth of 24 bits and a frame rate of 25 fps . This example has the following properties:

• pixels per frame = 640 * 480 = 307,200
• bits per frame = 307,200 * 24 = 7,372,800 = 7.37 Mbits
• bit rate (BR) = 7.37 * 25 = 184.25 Mbits / sec
• video size (VS) ^[3] = 184 Mbits / sec * 3600 sec = 662,400 Mbits = 82,800 Mbytes = 82.8 Gbytes

The most important properties are bit rate and video size . The formulas

BR = W * H * CD * FPS
VS = BR * T = W * H * CD * FPS * T
(units are: BR in bit / s, W and H in pixels, CD in bits, VS in bits, T in seconds)

while some secondary formulas are:

pixels_per_frame = W * H
 pixels_per_second = W * H * FPS
 bits_per_frame = W * H * CD

Interlacing

In interlaced video each frame is composed of two halves of an image . The first half contains only the odd-numbered lines of a full frame. The second half contains only the same-numbered lines. Those halves are referred to individually as fields . Two consecutive fields compose a full frame. If an interlaced video has a frame rate of 15 frames per second the field rate is 30 fields per second. All the properties and formulas discussed here apply to the second rate of the second rate.

Properties of compressed video

The above are accurate for uncompressed video . Because of the relatively high rate of uncompressed video, video compression is extensively used. In the box of the original bit. Assuming a compression algorithm That shrinks the input data by a factor of CF , the bit rate and video size Would equal to:

BR = W * H * CD * FPS / CF
VS = BR * T / CF

Note that it is not necessary that all elements are In practice they are not, so CF is the average factor of compression for all the frames taken together.

The above equation for the bit rate can be rewritten by combining the compression factor and the color depth like this:

BR = W * H * (CD / CF) * FPS

The value (CD / CF) represents the average bits per pixel (BPP) . As an example, if we have a color depth of 12bits / pixel and an algorithm that compresses at 40x, then BPP equals 0.3 (12/40). So in the case of a compressed video formula for bit rate is:

BR = W * H * BPP * FPS

The same formula is valid for uncompressed video because it can assume that the “compression” factor is 1 and that the average bits per pixel equal the color depth.

Bit rate and BPP

As is obvious by its definition bit rate is a measure of the rate of information content of the digital video stream. In the case of uncompressed video, a bit rate corresponds directly to the quality of the video (remember that bit rate is proportional to every property that affects the video quality ). Bit rate is an important property when transmitting video because the transmission link must be capable of supporting that bit rate. ^[4] Bit rate is also important when dealing with the storage of video because, as shown above, the video size is proportional to the bit rate and the duration. Bit rate of uncompressed video is too high for most practical applications. Video compressionis used to greatly reduce the bit rate. BPP is a measure of the efficiency of compression. A true-color video with no compression at all may have a BPP of 24 bits / pixel. Chroma subsampling can reduce the BPP to 16 or 12 bits / pixel. Applying jpeg compression on every frame can reduce the BPP to 8 or even 1 bits / pixel. Applying video compression algorithms like MPEG1 , MPEG2 or MPEG4 allows fractional BPP values.

Constant bit rate versus variable bit rate

As noted above BPP represents the average bits per pixel. There are compression algorithms that keep the BPP almost constant throughout the entire duration of the video. In this case we also get video output with a constant bit rate (CBR) . This CBR is suitable for real-time, non-buffered, fixed bandwidth streaming video (eg in videoconferencing). Noting that it can not be used at all because it is more severely impacted for high-speed computing. They keep it high while compressing complex scenes. This is one way to get the best quality at the smallest average bit rate (and the smallest file size accordingly). Of course when using this methodbit rate is variable because it tracks the variations of the BPP.

Technical overview

Standard film stocks such as 16 mm and 35 mm record at 24 frames per second . For video, there are two standard rates : NTSC , which shoot at 30 / 1.001 (about 29.97) frames per second or 59.94 fields per second, and PAL , 25 frames per second or 50 fields per second. Digital video cameras come in two different image capture formats: interlaced and deinterlaced / progressive scan. Interlaced cameras record the image of alternating sets of lines: the odd-numbered lines are scanned, and then the same-numbered lines are scanned, then the odd-numbered lines are scanned again, and so on. One set of odd or even lines is referred to as a “field”, and a consecutive pairing of two fields of opposite parity is called a frame . Deinterlaced cameras records each frame as distinct, with all scan lines being captured at the same time in time. THUS, interlaced video captures the szene samples motion twice as Often as progressive video does, for the Saami number of frames per second. Progressive-scan camcorders produce a bit sharper image. However, they may be used for 50 or 59.94 fields per second, especially if they use the 24 frames per second standard of film.

Digital video can be copied with no degradation in quality. No matter how many generations of a digital source is still in existence. However, a change in the parameters of a digital format can decrease the quality of the video due to new calculations that have to be made. NLE, or non-linear editing workstation, a computer-based device intended to edit video and audio. More and more, videos are being made available, is a relatively affordable consumer-grade computer hardware and software. However, such editing systems require ample disk space for video footage. The many video formats and parameters to be very difficult to make.

Digital video has a much lower cost than 35 mm film. In comparison to the high cost of film stock , the tape stock (or other electronic media used for digital video recording, such as flash memory or hard drive ) used for recording digital video is very inexpensive. Digital video as it is required to be viewed with the necessary chemical processing required by film. Also physical deliveries of tapes and broadcasts do not apply anymore. Digital television(including higher quality HDTV ) started in the early 2000s. Digital video is also used in modern mobile phones and video conferencingsystems. Digital video is also used for Internet distribution of media, including streaming videoand peer-to-peer movie distribution. However, there are lots of TV-stations not broadcasting in HD, due to restricted budgets for new equipment for HD processing.

Many types of video compression for digital video over the internet and on optical disks. Sorenson, H.264 and more recently Apple ProRes specifically for HD. Probably the most widely used formats for delivering video MPEG4, Quicktime, Flash and Windows Media, while MPEG2 is used almost exclusively for DVDs, providing an exceptional image in minimal size due to a high level of CPU consumption to decompress.

As of 2011 , the highest resolution demonstrated for digital video generation is 35 megapixels (8192 x 4320). The highest speed is attained in industrial and scientific high speed cameras that are capable of filming 1024×1024 video at up to 1 million frames per second for brief periods of recording.

Interfaces and cables

Many interfaces have been designed specifically to handle the requirements of uncompressed digital video (from roughly 400 Mbit / s to 10 Gbit / s):

• High-Definition Multimedia Interface
• Digital Visual Interface
• Serial Digital Interface
• DisplayPort
• Digital component video
• Unified Display Interface
• FireWire
• USB

The following interface has been designed for carrying MPEG -Transported video:

• DVB – ASI

Compressed video is also using UDP – IP over Ethernet . Two approaches exist for this:

• Using RTP as a wrapper for video packets
• 1-7 MPEG Transport Packets are placed directly in the UDP packet

Storage formats

Encoding

All current formats, which are listed below, are PCM based.

• CCIR 601 used for broadcast stations
• MPEG-4 good for online distribution of large videos and video recorded to flash memory
• MPEG-2 used for DVDs, Super-VCDs, and many broadcast television formats
• MPEG-1 used for video CDs
• H.261
• H.263
• H.264 also known as MPEG-4 Part 10 , or as AVC , used for Blu-ray Discs and some broadcast television formats
• Theora used for video on Wikipedia

Tapes

• Betacam SX , Betacam IMX , Digital Betacam , or DigiBeta – Commercial video systems by Sony , based on original Betamax technology
• D-VHS – MPEG-2 format data recorded on a tape similar to S-VHS
• D1 , D2 , D3 , D5 , D9 (also known as Digital-S) – various SMPTE commercial digital video standards
• Digital8 – DV-format data recorded on Hi8- compatible cassettes; largely a consumer format
• DV , MiniDV – used in today’s videotape-based consumer camcorders; designed for high quality and easy editing; can also record high-definition data ( HDV ) in MPEG-2 format
• DVCAM , DVCPRO – used in professional broadcast operations; similar to DV but generally considered more robust; though DV-compatible, these formats have better audio handling.
• DVCPRO50 , DVCPRO HD support higher bandwidths as compared to Panasonic’s DVCPRO.
• HDCAM was introduced by Sony as a high-definition alternative to DigiBeta.
• MicroMV – MPEG-2-format data recorded on a very small, matchbook-sized cassette; obsolete
• ProHD – name used by JVC for MPEG-2-based professional camcorders

Discs

• Blu-ray Disc
• DVD
• VCD

See also

Notes

References