Video
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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.
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 celluloid film when recorded by
mechanical cameras, in PAL or NTSC electric signals when recorded 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, 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 streamsNumber 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. To achieve the
illusion of a moving image, the minimum frame rate is about ten
frames per second. Film is shot at the slower frame rate of 24fps.InterlacingVideo 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
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 pixels 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 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. |
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