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Video

2007 Schools Wikipedia Selection. Related subjects: Media

          For help with video on Wikipedia, see Wikipedia:Media help

   Video is the technology of electronically capturing, recording,
   processing, storing, transmitting, and reconstructing a sequence of
   still images which represent 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 on through the Internet as video clips or streaming media
   clips on computer monitors.

   Video is different than film, which captures a moving image as a
   sequence of still pictures photographically.

Description

   Analog video standard: bright green - NTSC, yellow - PAL, or switching
   to PAL, orange - SECAM, olive - no information
   Enlarge
   Analog video standard: bright green - NTSC, yellow - PAL, or switching
   to PAL, orange - SECAM, olive - no information

   The term video (from the Latin for "I see") 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, 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 ten 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
   consisting of the odd-numbered lines and the even 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

   Comparison of TV resolutions
   Enlarge
   Comparison of TV resolutions

   The size of a video image is measured in pixels for digital video or
   horizontal scan lines for analog video. Standard-definition television
   ( SDTV) is specified as 720/704/640×480i60 for NTSC and 768/720×576i50
   for PAL or SECAM resolution. 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

   Comparison of common cinematography and traditional television (green)
   aspect ratios.
   Enlarge
   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
   1.37:1.

   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 and 16:9 (which is
   the anamorphic widescreen format) if the pixels are fat.

Colour space and bits per pixel

   Example of U-V color plane, Y value=0.5
   Enlarge
   Example of U-V colour plane, Y value=0.5

   Colour model name describes the video colour representation. YIQ is
   used in NTSC television. It corresponds closely to the YUV scheme used
   in 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. 4:4:4, 4:2:2, 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 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) 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
   colour 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 HD Blu-ray disks will greatly improve the 3D
   effect, in colour coded stereo programs. The first commercially
   available HD players are expected to debut at the 2006 NAB Show in Las
   Vegas in April. See articles Stereoscopy and 3-D film.

Video formats

   Video Display Standards Video Connection Standards
     * New digital:
          + ATSC (USA, Canada, etc., Advanced Television Systems
            Committee)
          + 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.)
               o PALplus (PAL extension. Europe only)
               o PAL-M (PAL variation. Brazil)
          + SECAM (France, ex-USSR, Central Africa)

     * Composite video (1 RCA or BNC)
     * Component video (3 RCA or BNC)
          + D4 video connector (new for HDTV)
     * S-Video (from Separated Video, 1 mini-DIN)
     * SCART (used in Europe)
     * DVI (uncompressed video only). HDCP optional
     * HDMI (uncompressed video & audio). HDCP mandatory.
     * RF connectors (from Radio Frequency coaxial connector)
          + BNC (Bayonet Niell-Concelman)
          + C connector (Concelman connector)
          + GR connector (General Radio connector)
          + F connector (used for U.S. domestic television installations)
          + IEC 169-2 (IEC connector, used mostly in the UK)
          + N connector (Niell connector)
          + TNC connector (Threaded Niell-Concelman)
          + UHF connector (e.g. PL-259/SO-239)
          + SDI and HD-SDI
     * VGA connector (DB-9/15 or mini sub D15)
     * Mini-VGA (used for laptops)

   Analog Tape Formats (See Analog television)

   Digital Tape Formats (See Digital video)
     * Ampex
     * VERA (BBC experimental format ca. 1958)
     * U-matic (Sony)
     * Betamax (Sony)
     * Betacam
     * Betacam SP
     * 2" Quadruplex videotape ( Ampex)
     * 1" Type C videotape ( Ampex and Sony)
     * VCR, VCR-LP, SVR
     * VHS ( JVC)
     * S-VHS ( JVC)
     * VHS-C ( JVC)
     * Video 2000 ( Philips)
     * Video8
     * Video Hi8

     * D1 (Sony)
     * D2 (Sony)
     * D3
     * D4
     * D5 HD
     * Digital Betacam (Sony)
     * Betacam IMX (Sony)
     * HDV
     * ProHD ( JVC)
     * D-VHS ( JVC)
     * DV
     * MiniDV
     * MicroMV
     * Digital8 (Sony)

   Optical Disc Storage Formats

   Digital Encoding Formats
     * DVD (was Super Density Disc, DVD Forum)
     * Laserdisc (old, MCA and Philips)
     * Blu-ray Disc (Sony)
     * Enhanced Versatile Disc (EVD, Chinese government-sponsored)
     * HD DVD ( Hitachi and Toshiba)

     * CCIR 601 ( ITU-T)
     * M-JPEG ( ISO)
     * MPEG-1 ( ISO)
     * MPEG-2 ( ITU-T + ISO)
     * MPEG-4 ( ISO)
     * H.261 ( ITU-T)
     * H.263 ( ITU-T)
     * H.264/MPEG-4 AVC ( ITU-T + ISO)
     * VC-1 ( SMPTE)
     * Ogg- Theora



                        Industrial & home video media
                                Magnetic tape

      VERA (1952) - 2 inch Quadruplex videotape (1956) - 1 inch type A
    videotape (1965) - U-matic (1969) - Video Cassette Recording (1972) -
     V-Cord (1974) - VX (aka "The Great Time Machine") (1974) - Betamax
      (1975) - 1 inch type B videotape (1976) - 1 inch type C videotape
     (1976) - VHS (1976) - Video 2000 (1979) - VHS-C (1982) - M (1982) -
   Betacam (1982) - Video8 (1985) - MII (1986) - D1 (1986) - S-VHS (1987)
      - D2 (1988) - D3 (1991) - D5 (1994) - Digital-S (D9) (199?) - Hi8
     (1998) - S-VHS-C (1987) - W-VHS (1992) - DV (1995) - Betamax HDCAM
            (1997) - D-VHS (1998) - Digital8 (1999) - HDV (2003)
                                Optical discs

      Laserdisc (1978) - Laserfilm (1984) - CD Video - VCD (1993) - DVD
   (1996) - MiniDVD - CVD (1998) - SVCD (1998) - FMD (2000) - EVD (2003) -
    UMD (2005) - HD DVD (2006) - Blu-ray Disc (BD) (2006) - DMD (2006?) -
                          AVCHD (2006) - HVD (TBA)
                             Grooved Videodiscs

                      SelectaVision (1981) - VHD (1983)

   Retrieved from " http://en.wikipedia.org/wiki/Video"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
