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VIDEO ENCYCLOPEDIA

2. 11. 2012

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Video

   Also found in: Dictionary/thesaurus, Acronyms, Encyclopedia, Hutchinson  0.01 sec.
Video (Latin for "I see", first person singular present, indicative of videre, "to see") is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion. Video technology was first developed for television systems, but has been further developed in many formats to allow for consumer video recording. Video can also be viewed through the Internet as video clips or streaming media clips on computer monitors.

Description of video

Enlarge picture
Analog video standards worldwide      NTSC      PAL or switching to PAL      SECAM      No information


The term video commonly refers to several storage formats for moving pictures: digital video formats, including DVD, QuickTime, and MPEG-4; and analog videotapes, including VHS and Betamax. Video can be recorded and transmitted in various physical media: in magnetic tape when recorded as PAL or NTSC electric signals by video cameras, or in MPEG-4 or DV digital media when recorded by digital cameras.

Quality of video essentially depends on the capturing method and storage used. Digital television (DTV) is a relatively recent format with higher quality than earlier television formats and has become a standard for television video. (See List of digital television deployments by country.)

3D-video, digital video in three dimensions, premiered at the end of 20th century. Six or eight cameras with realtime depth measurement are typically used to capture 3D-video streams. The format of 3D-video is fixed in MPEG-4 Part 16 Animation Framework eXtension (AFX).

In the UK, Australia, The Netherlands and New Zealand, the term video is often used informally to refer to both video recorders and video cassettes; the meaning is normally clear from the context.

Characteristics of video streams

Number of frames per second

Frame rate, the number of still pictures per unit of time of video, ranges from six or eight frames per second (fps) for old mechanical cameras to 120 or more frames per second for new professional cameras. PAL (Europe, Asia, Australia, etc.) and SECAM (France, Russia, parts of Africa etc.) standards specify 25 fps, while NTSC (USA, Canada, Japan, etc.) specifies 29.97 fps. Film is shot at the slower frame rate of 24fps, which complicates slightly the process of transferring a cinematic motion picture to video. To achieve the illusion of a moving image, the minimum frame rate is about fifteen frames per second.

Interlacing

Video can be interlaced or progressive. Interlacing was invented as a way to achieve good visual quality within the limitations of a narrow bandwidth. The horizontal scan lines of each interlaced frame are numbered consecutively and partitioned into two fields: the odd field (upper field) consisting of the odd-numbered lines and the even field (lower field) consisting of the even-numbered lines. NTSC, PAL and SECAM are interlaced formats. Abbreviated video resolution specifications often include an i to indicate interlacing. For example, PAL video format is often specified as 576i50, where 576 indicates the vertical line resolution, i indicates interlacing, and 50 indicates 50 fields (half-frames) per second.

In progressive scan systems, each refresh period updates all of the scan lines. The result is a higher perceived resolution and a lack of various artifacts that can make parts of a stationary picture appear to be moving or flashing.

A procedure known as deinterlacing can be used for converting an interlaced stream, such as analog, DVD, or satellite, to be processed by progressive scan devices, such as TFT TV-sets, projectors, and plasma panels. Deinterlacing cannot, however, produce a video quality that is equivalent to true progressive scan source material.

Video resolution

Enlarge picture
Comparison of TV resolutions
The size of a video image is measured in pixels for digital video, or horizontal scan lines and vertical lines of resolution for analog video. In the digital domain (e.g. DVD) standard-definition television (SDTV) is specified as 720/704/640×480i60 for NTSC and 768/720×576i50 for PAL or SECAM resolution. However in the analog domain, the number of visible scanlines remains constant (486 NTSC/576 PAL) while the horizontal measurement varies with the quality of the signal: approximately 320 pixels per scanline for VCR quality, 400 pixels for TV broadcasts, and 720 pixels for DVD sources. Aspect ratio is preserved because of non-square "pixels".
New high-definition televisions (HDTV) are capable of resolutions up to 1920×1080p60, i.e. 1920 pixels per scan line by 1080 scan lines, progressive, at 60 frames per second.

Video resolution for 3D-video is measured in voxels (volume picture element, representing a value in three dimensional space). For example 512×512×512 voxels resolution, now used for simple 3D-video, can be displayed even on some PDAs.

Aspect ratio

Enlarge picture
Comparison of common cinematography and traditional television (green) aspect ratios.


Aspect ratio describes the dimensions of video screens and video picture elements. The screen aspect ratio of a traditional television screen is 4:3, or 1.33:1. High definition televisions use an aspect ratio of 16:9, or about 1.78:1. The aspect ratio of a full 35 mm film frame with soundtrack (also known as "Academy standard") is around 2.37:1.

Pixels on computer monitors are usually square, but pixels used in digital video often have non-square aspect ratios, such as those used in the PAL and NTSC variants of the CCIR 601 digital video standard, and the corresponding anamorphic widescreen formats. Therefore, an NTSC DV image which is 720 pixels by 480 pixels is displayed with the aspect ratio of 4:3 (which is the traditional television standard) if the pixels are thin and displayed with the aspect ratio of 16:9 (which is the anamorphic widescreen format) if the pixels are fat.

Color space and bits per pixel



Color model name describes the video color representation. YIQ was used in NTSC television. It corresponds closely to the YUV scheme used in NTSC and PAL television and the YDbDr scheme used by SECAM television.

The number of distinct colours that can be represented by a pixel depends on the number of bits per pixel (bpp). A common way to reduce the number of bits per pixel in digital video is by chroma subsampling (e.g. , , ).

Video quality

Video quality can be measured with formal metrics like PSNR or with subjective video quality using expert observation.

The subjective video quality of a video processing system may be evaluated as follows:
  • Choose the video sequences (the SRC) to use for testing.
  • Choose the settings of the system to evaluate (the HRC).
  • Choose a test method for how to present video sequences to experts and to collect their ratings.
  • Invite a sufficient number of experts, preferably not fewer than 15.
  • Carry out testing.
  • Calculate the average marks for each HRC based on the experts' ratings.
Many subjective video quality methods are described in the ITU-T recommendation BT.500. One of the standardized method is the Double Stimulus Impairment Scale (DSIS). In DSIS, each expert views an unimpaired reference video followed by an impaired version of the same video. The expert then rates the impaired video using a scale ranging from "impairments are imperceptible" to "impairments are very annoying".

Video compression method (digital only)

A wide variety of methods are used to compress video streams. Video data contains spatial and temporal redundancy, making uncompressed video streams extremely inefficient. Broadly speaking, spatial redundancy is reduced by registering differences between parts of a single frame; this task is known as intraframe compression and is closely related to image compression. Likewise, temporal redundancy can be reduced by registering differences between frames; this task is known as interframe compression, including motion compensation and other techniques. The most common modern standards are MPEG-2, used for DVD and satellite television, and MPEG-4, used for home video.

Bit rate (digital only)

Bit rate is a measure of the rate of information content in a video stream. It is quantified using the bit per second (bit/s or bps) unit or Megabits per second (Mbit/s). A higher bit rate allows better video quality. For example VideoCD, with a bit rate of about 1 Mbit/s, is lower quality than DVD, with a bit rate of about 5 Mbit/s. HDTV has a still higher quality, with a bit rate of about 20 Mbit/s.

Variable bit rate (VBR) is a strategy to maximize the visual video quality and minimize the bit rate. On fast motion scenes, a variable bit rate uses more bits than it does on slow motion scenes of similar duration yet achieves a consistent visual quality. For real-time and non-buffered video streaming when the available bandwidth is fixed, e.g. in videoconferencing delivered on channels of fixed bandwidth, a constant bit rate (CBR) must be used.

Stereoscopic

Stereoscopic video requires either two channels — a right channel for the right eye and a left channel for the left eye or two overlayed color coded layers. This left and right layer technique is occasionally used for network broadcast, or recent "anaglyph" releases of 3D movies on DVD. Simple Red/Cyan plastic glasses provide the means to view the images discretely to form a stereoscopic view of the content.* New HD DVD and Blu-ray Discs will greatly improve the 3D effect, in color coded stereo programs. The first commercially available HD players were expected to debut at the 2006 NAB Show in Las Vegas in April. See articles Stereoscopy and 3-D- Max film.

Video formats

    Video display standards Video connection standards
    • New digital:
    • ATSC (USA, Canada, etc.)
    • DVB (European, Digital Video Broadcasting)
    • ISDB (Japanese, Integrated Services Digital Broadcasting)
    • Old analog:
    • MAC (Europe - Obsolete)
    • MUSE (Japan-analog HDTV)
    • NTSC (USA, Canada, Japan, etc.)
    • PAL (Europe, Asia, Australia, etc.)
    • PALplus (PAL extension. Europe only)
    • PAL-M (PAL variation. Brazil)
    • SECAM (France, ex-USSR, Central Africa)
    •  
    Analog tape formats (see analog television) Digital tape formats (see digital video)
    Optical disc storage formats Digital encoding formats

      See also

      External links

      Latin}}} 
      Official status
      Official language of: Vatican City
      Used for official purposes, but not spoken in everyday speech
      Regulated by: Opus Fundatum Latinitas
      Roman Catholic Church
      Language codes
      ISO 639-1: la
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      grammatical number is grammatical category of nouns, pronouns, and verb agreement that expresses count distinctions (such as "one" or "more than one").[1]
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      Grammatical tense is a way languages express the time at which an event described by a sentence occurs. In English, this is a property of a verb form, and expresses only time-related information.
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      Electronics is the study of the flow of charge through various materials and devices such as, semiconductors, resistors, inductors, capacitors, nano-structures, and vacuum tubes. All applications of electronics involve the transmission of power and possibly information.
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      Videography refers to the process of capturing moving images on electronic media (e.g., videotape, hard disk, or solid state storage, streaming media). The term includes methods of electronic production and post production.
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      A still image is a single image, as distinguished from a moving image (i.e. a movie). This phrase is used in photography, visual media and the computer industry to emphasize that one is not talking about movies, or in very precise or pedantic technical writing such as a standard
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      In TV, stage plays and movies a scene is a part of the action in a single location. Due to the ability to edit recorded visual works, it is typically much shorter than a scene in theater.
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      If you are prevented from editing this page, and you wish to make a change, please discuss changes on the talk page, request unprotection, log in, or .
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      Television (often abbreviated to TV, T.V., or more recently, tv; sometimes called telly, the tube, boob tube, or idiot box in British English) is a widely used telecommunication system for broadcasting and receiving moving pictures
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      Internet is a worldwide, publicly accessible series of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government
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      Video clips are short clips of video, usually part of a longer piece.

      Video clips in digital format are often found on the internet where the massive influx of new video clips during 2006 was hailed as a new phenomenon having a profound impact on both the internet and other
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      This article relies largely or entirely upon a .
      Please help [ improve this article] by introducing appropriate of additional sources. ()
      This article has been tagged since October 2007.
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      computer is a machine which manipulates data according to a list of instructions.

      Computers take numerous physical forms. The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1941), although the computer concept and various machines
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      A computer display monitor, usually called simply a monitor, is a piece of electrical equipment which displays viewable images generated by a computer without producing a permanent record.
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      The term digital signal is used to refer to more than one concept. It can refer to discrete-time signals that are digitized, or to the waveform signals in a digital system.
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      DVD

      Media type: Optical disc
      Capacity: 4.7 GB (single layer), 8.5 GB (dual layer)
      Usage: Data storage, audio, video, games

      Optical disc authoring
      • Optical disc
      • Optical disc image
      • Recorder hardware
      • Authoring software
      •  

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      Maintainer: Apple Inc.

      OS: Mac OS X, Windows XP and Vista

      Use: Multimedia framework
      License: Proprietary
      Website: www.apple.com/quicktime/ QuickTime is a multimedia framework developed by Apple Inc.
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      MPEG-4 is a standard used primarily to compress audio and visual (AV) digital data. Introduced in late 1998, it is the designation for a group of audio and video coding standards and related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG) under the formal
      ..... Click the link for more information.
      An analog or analogue signal is any time continuous signal where some time varying feature of the signal is a representation of some other time varying quantity. It differs from a digital signal in that small fluctuations in the signal are meaningful.
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      Videotape is a means of recording images and sound onto magnetic tape as opposed to movie film. In most cases, a helical scan video head rotates against the moving tape to record the data in two dimensions, because video signals have a very high bandwidth, and static heads would
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      Video Home System

      Top view of VHS cassette with ruler for scale
      Media type: Video recording media
      Encoding: FM on magnetic tape
      Developed by: JVC (Japan Victor Company)
      Usage: Audio/Video Storage

      The Video Home System [1]
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      Betamax
      Media type: Video recording media
      Encoding: Magnetic tape
      Developed by: Sony
      Usage: Video storage

      Sony's Betamax is the 12.
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      PAL, short for Phase Alternating Line, is a colour encoding system used in broadcast television systems in large parts of the world. Other common analogue television systems are SECAM and NTSC.
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      A video camera is a camera used for electronic motion picture acquisition, initially developed by the television industry but now common in other applications as well. The earliest video cameras were those of John Logie Baird, based on the electromechanical Nipkow disk and used by
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      MPEG-4 is a standard used primarily to compress audio and visual (AV) digital data. Introduced in late 1998, it is the designation for a group of audio and video coding standards and related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG) under the formal
      ..... Click the link for more information.
      Digital Video (DV) is a digital video format launched in 1994, and, in its smaller tape form factor MiniDV, has since become a standard for home and semiprofessional video production; it is sometimes used for professional purposes as well, such as filmmaking and electronic
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      digital camera is an electronic device used to capture and store photographs digitally, instead of using photographic film like conventional cameras, or recording images in an analog format to magnetic tape like many video cameras.
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      This article is copied from an article on Wikipedia® - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the Wikipedia® encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.

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