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Video. Video is an electronic medium for the recording, copying and broadcasting of moving visual images.

Video

History[edit] Video technology was first[citation needed] developed for cathode ray tube (CRT) television systems, but several new technologies for video display devices have since been invented. Charles Ginsburg led an Ampex research team developing one of the first practical video tape recorder (VTR). In 1951 the first video tape recorder captured live images from television cameras by converting the camera's electrical impulses and saving the information onto magnetic video tape. Video recorders were sold for $50,000 in 1956, and videotapes cost $300 per one-hour reel.[1] However, prices gradually dropped over the years; in 1971, Sony began selling videocassette recorder (VCR) decks and tapes to the public.[2] After the invention of the DVD in 1997 and Blu-ray Disc in 2006, sales of videotape and recording equipment plummeted.

Motion compensation. Visualization of MPEG block motion compensation.

Motion compensation

Blocks that moved from one frame to the next are shown as white arrows, making the motions of the different platforms and the character clearly visible. Motion compensation is an algorithmic technique employed in the encoding of video data for video compression, for example in the generation of MPEG-2 files.

Motion interpolation. Motion interpolation or motion-compensated frame interpolation (MCFI) is a form of video processing in which intermediate animation frames are generated between existing ones, in an attempt to make animation more fluid, and to compensate for display motion blur.

Motion interpolation

Applications[edit] Software[edit] Some video software suites and plugins offer motion-interpolation effects to enhance digitally-slowed video. Raster graphics. Interleaving. CRT. Cutaway rendering of a color CRT:1.

CRT

Three Electron guns (for red, green, and blue phosphor dots)2. Electron beams3. Focusing coils4. Deflection coils5. Anode connection6. Overscan. Overscan is the term used to describe the situation when not all of a televised image is present on a viewing screen.

Overscan

It exists because television sets from the 1930s through the 1990s were highly variable in how the video image was positioned within the borders of the cathode ray tube (CRT) screen. The solution was to have the monitor show less than the full image ie. with the edges "outside" the viewing area of the tube. In this way the image seen never showed black borders caused by either improper centering or non-linearity in the scanning circuits or variations in power supply voltage all of which could cause the image to "shrink" in size and reveal the edge of the picture.

With the ending of CRT displays, this issue has largely (but not completely) disappeared. YUV pixel formats. YUV formats fall into two distinct groups, the packed formats where Y, U (Cb) and V (Cr) samples are packed together into macropixels which are stored in a single array, and the planar formats where each component is stored as a separate array, the final image being a fusing of the three separate planes.

YUV pixel formats

In the diagrams below, the numerical suffix attached to each Y, U or V sample indicates the sampling position across the image line, so, for example, V0 indicates the leftmost V sample and Yn indicates the Y sample at the (n+1)th pixel from the left. Subsampling intervals in the horizontal and vertical directions may merit some explanation. Chrominance. Luminance only, Chrominance only, and full color image. History[edit] The use of two channels, one transmitting the predominating color (signal T), and the other the mean brilliance (signal t) output from a single television transmitter to be received not only by color television receivers provided with the necessary more expensive equipment, but also by the ordinary type of television receiver which is more numerous and less expensive and which reproduces the pictures in black and white only.

Previous schemes for color television systems, which were incompatible with existing monochrome receivers, transmitted RGB signals in various ways. Television standards[edit] In analog television, chrominance is encoded into a video signal using a subcarrier frequency. MPEG. MPEG logo Sub Groups[edit] ISO/IEC JTC1/SC29/WG11 – Coding of moving pictures and audio has following Sub Groups (SG):[6] RequirementsSystemsVideoAudio3D Graphics CompressionTestCommunication Cooperation with other groups[edit]

MPEG

MPEG-2 system. MPEG-2 (aka H.222/H.262 as defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information".[1] It describes a combination of lossy video compression and lossy audio data compression methods, which permit storage and transmission of movies using currently available storage media and transmission bandwidth.

MPEG-2 system

Main characteristics[edit] MPEG-2 is widely used as the format of digital television signals that are broadcast by terrestrial (over-the-air), cable, and direct broadcast satellite TV systems. It also specifies the format of movies and other programs that are distributed on DVD and similar discs. TV stations, TV receivers, DVD players, and other equipment are often designed to this standard. MPEG-2 was the second of several standards developed by the Moving Pictures Expert Group (MPEG) and is an international standard (ISO/IEC 13818). PSI. Program-specific information (PSI) is metadata about a program (channel) and part of an MPEG transport stream.

PSI

The PSI data as defined by ISO/IEC 13818-1 (MPEG-2 Part 1: Systems) includes four tables: PAT (program association table)CAT (conditional access table)PMT (program map table)NIT (network information table) PSI is carried in the form of a table structure. Each table structure is broken into sections and can span multiple transport stream packets. DSM-CC. Digital storage media command and control (DSM-CC) is a toolkit for developing control channels associated with MPEG-1 and MPEG-2 streams.

DSM-CC

It is defined in part 6 of the MPEG-2 standard (Extensions for DSM-CC) and uses a client/server model connected via an underlying network (carried via the MPEG-2 multiplex or independently if needed). DSM-CC may be used for controlling the video reception, providing features normally found on Video Cassette Recorders (VCR) (fast-forward, rewind, pause, etc.). It may also be used for a wide variety of other purposes including packet data transport. It is defined by a series of weighty standards, principally MPEG-2 ISO/IEC 13818-6 (part 6 of the MPEG-2 standard). PES. A typical method of transmitting elementary stream data from a video or audio encoder is to first create PES packets from the elementary stream data and then to encapsulate these PES packets inside Transport Stream (TS) packets or Program Stream (PS) packets.

The TS packets can then be multiplexed and transmitted using broadcasting techniques, such as those used in an ATSC and DVB. Transport Streams and Program Streams are each logically constructed from PES packets. MPEG-2 video compression. Video compression picture types. In the field of video compression a video frame is compressed using different algorithms with different advantages and disadvantages, centered mainly around amount of data compression. These different algorithms for video frames are called picture types or frame types. The three major picture types used in the different video algorithms are I, P and B. They are different in the following characteristics: I‑frames are the least compressible but don't require other video frames to decode.P‑frames can use data from previous frames to decompress and are more compressible than I‑frames.B‑frames can use both previous and forward frames for data reference to get the highest amount of data compression.

DCT. Entropy coding. Huffman coding. Huffman tree generated from the exact frequencies of the text "this is an example of a huffman tree". The frequencies and codes of each character are below. Encoding the sentence with this code requires 135 bits, as opposed to 288 bits if 36 characters of 8 bits were used. (This assumes that the code tree structure is known to the decoder and thus does not need to be counted as part of the transmitted information.) MPEG PS. Program streams are used on DVD-Video discs and HD DVD video discs, but with some restrictions and extensions.[9][10] The filename extensions are VOB and EVO respectively. Coding structure[edit] Program streams are created by combining one or more Packetized Elementary Streams (PES), which have a common time base, into a single stream.

It is designed for reasonably reliable media such as disks, in contrast to MPEG transport stream which is for data transmission in which loss of data is likely. Program streams have variable size records and minimal use of start codes which would make over the air reception difficult, but has less overhead. Program stream coding layer allows only one program of one or more elementary streams to be packaged into a single stream, in contrast to transport stream, which allows multiple programs.[7] MPEG TS. Diff. TS vs PS.