Video 32441 225817783 2008-07-15T15:24:45Z MrOllie 6908984 [[WP:UNDO|Undid]] revision 225816514 by [[Special:Contributions/203.215.88.10|203.215.88.10]] ([[User talk:203.215.88.10|talk]]) {{Otheruses}} {{For|films or movies|Film}} {{for|the use of video in Wikipedia articles|Wikipedia:Creation and usage of media files}} '''Video''' is the technology of [[electronics|electronically]] [[Videography|capturing]], [[recording]], processing, storing, transmitting, and reconstructing a sequence of [[still image]]s representing [[Scene (film)|scenes]] in motion. ==History== Video [[technology]] was first developed for [[cathode ray tube]] [[television]] systems, but several new technologies for video [[display devices]] have since been invented. Standards for [[television sets]] and [[computer monitors]] have tended to evolve independently, but advances in computer performance and [[digital television]] broadcasting and recording are producing some convergence. Computers can now display television and film-style [[video clips]] and [[streaming media]], encouraged by increased processor speed, storage capacity, and [[broadband]] access to the [[Internet]]. General-purpose computing hardware can now be used to capture, store, edit, and transmit television and movie content, as opposed to older dedicated analog technologies. {{Expand-section|date=June 2008}} ==Description of video== [[Image:NTSC-PAL-SECAM.svg|thumb|300px|Analog video standards worldwide {{legend|#70ff70| [[NTSC]]}} {{legend|yellow| [[PAL]] or switching to PAL}} {{legend|orange| [[SECAM]]}} {{legend|#9fdba4| No information}} ]] The term ''video'' (from Latin: "I see") commonly refers to several storage formats for moving eye pictures: [[digital (signal)|digital]] video formats, including [[DVD]], [[QuickTime]], and [[MPEG-4]]; and [[analog (signal)|analog]] [[videotape]]s, 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 camera]]s, or in [[MPEG-4]] or [[DV]] digital media when recorded by [[digital cameras]]. [[Video quality|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 [[3-D film|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 [[United Kingdom|UK]], [[Australia]], [[The Netherlands]], [[Finland]], [[Hungary]] and [[New Zealand]], the term ''video'' is often used informally to refer to both [[Videocassette recorder]]s and [[videotape|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 (''frame/s'') 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 frame/s, while [[NTSC]] (USA, Canada, Japan, etc.) specifies 29.97 frame/s. Film is shot at the slower frame rate of 24frame/s, which complicates slightly the process of transferring a cinematic motion picture to video. The minimum frame rate to achieve the illusion of a moving image is about fifteen frames per second. ===Interlacing=== Video can be [[interlaced]] or [[Progressive scan|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 [[Liquid crystal display television|TFT TV-sets]], projectors, and plasma panels. Deinterlacing cannot, however, produce a [[video quality]] that is equivalent to true progressive scan source material. ===Display resolution=== {{main|Display resolution}} [[Image:Vector Video Standards2.svg|thumb|240px|[[List of common resolutions|Common computer and TV display resolutions.]] ]] The size of a video image is measured in [[pixel]]s 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 ([[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 ([[high-definition television|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 [[voxel]]s (''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 [[personal digital assistant|PDA]]s. ===Aspect ratio=== [[Image:Aspect ratios.svg|thumbnail|250px|Comparison of common [[cinematography]] and traditional [[television]] (green) aspect ratios.]] [[Image:Pac-man.png|120px|thumb|left|Many arcade games use 3:4 portrait mode to efficiently utilize the entire display area.]] [[Aspect ratio (image)|Aspect ratio]] describes the dimensions of video screens and video picture elements. All popular video formats are rectilinear, and so can be described by a ratio between width and height. The screen aspect ratio of a traditional television screen is 4:3, or about 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. Ratios where the height is taller than the width are uncommon in general everyday use, but do have application in computer systems where the screen may be better suited for a vertical layout. The most common tall aspect ratio of 3:4 is referred to as ''portrait mode'' and is created by physically rotating the display device 90 degrees from the normal position. Other tall aspect ratios such as 9:16 are technically possible but rarely used. (For a more detailed discussion of this topic please refer to the [[page orientation]] article.) 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=== [[Image:YUV UV plane.png|thumb|100px|Example of U-V color plane, Y value=0.5]] ''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. [[4:2:2#4:4:4|4:4:4]], [[4:2:2#4:2:2|4:2:2]], [[4:2:0#4:2:0|4:2:0]]). === 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 [[Scientific method|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)=== {{main|Video compression}} A wide variety of methods are used to [[video compression|compress]] video streams. Video data contains spatial and temporal [[Redundancy (information theory)|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|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|constant bit rate (CBR)]] must be used. ===Stereoscopic=== ''Stereoscopic video'' can be created using several different methods: * two channels &mdash; a right channel for the right eye and a left channel for the left eye. Both channels may be viewed simultaneously by using [[light polarization | light-polarizing filters]] 90 degrees off-axis from each other on two video projectors. These separately polarized channels are viewed wearing eyeglasses with matching polarization filters. * one channel with 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. * One channel with alternating left/right frames for each eye, using [[LCD shutter glasses]] which read the frame sync from the [[VGA]] [[Display Data Channel]] to alternately cover each eye, so the appropriate eye sees the correct frame. This method is most common in computer [[virtual reality]] applications such as in a [[Cave Automatic Virtual Environment]], but reduces the effective video framerate to one-half of normal (for example, from 120Hz to 60Hz). New [[HD DVD]] and [[Blu-ray Disc]]s will greatly improve the sharpness and detail of the two-color 3D effect in color coded stereo programs. The first commercially available HD players were expected to debut at the 2006 [[National Association of Broadcasters|NAB]] Show in Las Vegas in April. See articles [[Stereoscopy]] and [[3D film]]. ==Video formats== There are different layers of video transmission and storage, each with its own set of formats to choose from. For transmission, there is a physical connector and signal protocol ("video connection standard" below). A given physical link can carry certain "display standards" which specify a particular refresh rate, [[display resolution]], and [[color space]]. There are a number of analog and digital tape formats, though digital video files can also be stored on a [[computer file system]] which have their own formats. In addition to the physical format used by the storage or transmission medium, the stream of ones and zeros that is sent must be in a particular digital video "encoding", of which a number are available. ===Video connectors, cables, and signal standards=== * See [[List of video connectors]] for information about physical connectors and related signal standards. ===Video display standards=== ====Digital television==== New formats for [[digital television]] broadcasts use the [[MPEG-2]] [[video codec]] and include: * [[ATSC Standards|ATSC]] - USA, Canada, etc.; a [[DVB]] video standard * [[Digital Video Broadcasting]] (DVB) - European * [[Integrated Services Digital Broadcasting]] (ISDB) - Japanese; also a [[DVB]] video standard ====Analog television==== [[Analog television]] broadcast standards include: * [[Multiplexed Analogue Components]] (MAC) - Europe, obsolete * [[Multiple sub-nyquist sampling Encoding]] (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 * [[Field-sequential color system]] - USA, Russia; obsolete * [[RS-343]] (military) An analog video format consists of more information than the visible content of the frame. Preceding and following the image are lines and pixels containing synchronization information or a time delay. This surrounding margin is known as a '''blanking interval''' or '''blanking region'''; the horizontal and vertical [[front porch]] and [[back porch]] are the building blocks of the blanking interval. Many countries are planning a [[digital switchover]] to cease using these analog formats via [[terrestrial television]] broadcast. However, analog television sets expecting these older standards as input will be able to display [[standard definition]] digital signals if coupled with a converter box. {{cleanup-merge}} <!-- The list in the template and the list above overlap considerably but not completely. --> {{Video formats}} ====Computer displays==== See [[Computer display standard]] for a list of standards used for computer monitors and comparison with those used for television. ===Analog tape formats=== *[[Ampex]] *[[VERA videotape format|VERA]] ([[BBC]] experimental format ca. 1958) *[[Philips videotape recorder EL3400 1" helical scan ca.1963]] *[[U-matic]] ([[Sony]]) *[[Betamax]] (Sony) *[[Betacam]] *[[Betacam SP]] *[[2" Quadruplex videotape]] ([[Ampex]]) *[[1" Type C videotape]] ([[Ampex]] and [[Sony]]) *[[1 inch type B videotape|1" Type B video tape]] ([[Robert Bosch GmbH|Bosch]]) *[[Philips Video Cassette Recording ca. 1971|VCR, VCR-LP, SVR]] *[[VHS]] ([[JVC]]) *[[S-VHS]] ([[JVC]]) *[[VHS-C]] ([[JVC]]) *[[Video 2000]] ([[Philips]]) *[[8 mm video format|Video8]] *[[8 mm video format|Video Hi8]] ===Digital tape formats=== *[[D1 (Sony)|D1]] ([[Sony]]) *[[D2 (video format)|D2]] ([[Sony]]) *[[D3 (video)|D3]] *[[D5 HD]] *[[Digital Betacam]] ([[Sony]]) *[[Betacam IMX]] ([[Sony]]) *[[HDV]] *[[ProHD]] ([[JVC]]) *[[D-VHS]] ([[JVC]]) *[[DV]] *[[MiniDV]] *[[MicroMV]] *[[Digital8]] ([[Sony]]) ===Optical disc storage formats=== *[[DVD]] (was [[Super Density Disc]], [[DVD Forum]]) *[[Laserdisc]] (old, [[Music Corporation of America|MCA]] and [[Philips]]) *[[Blu-ray Disc]] ([[Sony]]) *[[Enhanced Versatile Disc]] (EVD, Chinese government-sponsored) *[[HD DVD]] ([[NEC Corporation|NEC]] and [[Toshiba]]) ===Digital encoding formats=== *[[CCIR 601]] ([[ITU-T]]) *[[MJPEG|M-JPEG]] ([[International Organization for Standardization|ISO]]) *[[MPEG-1]] ([[International Organization for Standardization|ISO]]) *[[MPEG-2]] ([[ITU-T]] + [[International Organization for Standardization|ISO]]) *[[MPEG-4]] ([[International Organization for Standardization|ISO]]) *[[H.261]] ([[ITU-T]]) *[[H.263]] ([[ITU-T]]) *[[H.264/MPEG-4 AVC]] ([[ITU-T]] + [[International Organization for Standardization|ISO]]) *[[VC-1]] ([[SMPTE]]) *[[Ogg]]-[[Theora]] *{{see also|Video codec}} *{{see also|List of codecs}} {{homevid}} ==See also== * '''General''' ** [[sound reproduction|Audio]] ** [[List of video topics]] ** [[Video clip]] ** [[Video editing]] * '''Video format''' ** [[Film formats]] ** [[Television]] ** [[Digital video]] ** [[Digital television]] ** [[Satellite television]] ** [[Analog television]] ** [[Cable television]] ** [[Interlaced]] ** [[Progressive scan]] ** [[Telecine]] ** [[Video codec]] ** [[Timecode]] ** [[Color space]] * '''Video usage''' ** [[Video art]] ** [[Closed-circuit television]] ** [[Video projector]] ** [[Video synthesizer]] ** [[Video teleconference]] ** [[Video production]] ** [[Optical feedback]] ** [[Fulldome|Fulldome video]] * '''Video screen recording''' ** [[Screencast]] == External links == <!-- PLEASE ONLY LIST SITES THAT EXPLAIN ABOUT VIDEO, NOT VIDEO HOSTING SITES. DO NOT LIST YOUTUBE. --> * {{dmoz|Business/Arts_and_Entertainment/Media_Production/Video/|Video as Media Production}} * {{dmoz|Arts/Video/|Video as Arts}} *[http://lurkertech.com/lg/video-systems Programmer's Guide to Video Systems: in-depth technical info on 480i,576i,1080i,720p,etc.] [[Category:Video| ]] [[Category:Digital television]] [[Category:Film and video technology]] [[Category:High-definition television]] [[Category:Video formats]] [[Category:Display technology]] [[ar:فيديو]] [[bs:Video]] [[ca:Vídeo]] [[cs:Video]] [[da:Video]] [[de:Videotechnik]] [[es:Video]] [[eo:Video]] [[eu:Bideo]] [[fa:ویدیو]] [[fr:Vidéo]] [[ga:Físeán]] [[gl:Vídeo]] [[ko:비디오]] [[hr:Video]] [[id:Video]] [[is:Myndband]] [[it:Video]] [[he:וידאו]] [[ms:Video]] [[nl:Video]] [[ja:ビデオ]] [[no:Video]] [[pt:Vídeo]] [[ru:Видео]] [[simple:Video]] [[sk:Videotechnika]] [[sl:Video]] [[sr:Видео]] [[fi:Video]] [[sv:Video]] [[th:วิดีโอ]] [[vi:Phim video]] [[tr:Video]] [[uk:Відео]] [[yi:ווידיאו]] [[zh:视频]]