Information AboutVideos |
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Video is the technology of capturing, recording, processing, transmitting, and reconstructing Moving Pictures , typically using celluloid film, electronic signals, or digital media, primarily for viewing on Television or Computer Monitor s. DESCRIPTION The term ''video'' (from the , in PAL or NTSC electric signals when recorded by Video Camera s, 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. To achieve the illusion of a moving image, the minimum frame rate is about ten frames per second. Interlacing Video can be Interlace d 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 horizontal resolution, ''i'' indicates interlacing, and ''50'' indicates 50 (single-field) frames per second. In ''progressive scan'' systems, each frame includes all of the scan lines. The result is a much higher perceived resolution. 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 inevitably decreases Video Quality . Video resolution The size of a video image is measured in Pixel s for digital video or horizontal scan lines for analog video. Standard-definition television ( SDTV ) is specified as ''640×480i60'' for NTSC and ''720×576i50'' for PAL or SÉCAM 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 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 PDA s. Aspect ratio and 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 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. Color space and Bits per pixel ''Color model name'' describes the video color representation. '' YIQ '' is used in NTSC television. It corresponds closely to the '' YUV '' scheme used in PAL television and the '' YDbDr '' scheme used by SÉCAM 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 ). 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:
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 10 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 discreetly to form a stereoscopic view of the content. New HD DVD and HD Blu-ray disks will greatly improve the 3D effect, in color 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 SEE ALSO
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