Audio and Video

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Posted by kaori 04/06/2009 @ 00:14

Tags : audio and video, technology

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Audio and video interfaces and connectors

2.5 mm (3/32") mono (TS), 3.5 mm (1/8") mono and stereo (TRS), and 6.3 mm (1/4") stereo (TRS) jack plugs

Audio and video standards entail the definition of hardware interfaces ("interfaces" for short).

Interfaces define the physical characteristics of the interconnection of electrical equipment. This includes, the type and numbers of wires, the strength and frequency of the signal. It also includes the connectors, that is, the design of the plugs and sockets.

An interfaces may define a connector that is used only by that interface (Eg Digital Visual Interface). An interface may define a connector that is also used by another interface. For example RCA connectors are defined both by the composite video and component video interfaces.

S/PDIF (Sony/Philips Digital Interconnect Format). Via Coaxial or Optical cables.

Composite. Often designated by the CVBS acronym, meaning "Color, Video, Blank and Sync".

S-Video aka Separate Video. Carries standard definition video and does not carry audio on the same cable.

VIVO = Mini-DIN 9 Pin with breakout cable.

The PC System Design Guide (also known as the PC 97, PC 98, PC 99, or PC 2001 specification) is a series of hardware design requirements and recommendations for IBM PC compatible personal computers, compiled by Microsoft and Intel Corporation during 1997–2001.

PC 99 introduced a color code for the various standard types of plugs and connectors used on PCs.

Generally via electrical coaxial cable (with RCA jacks) or optical fibre (TOSLINK).

Note that there are no differences in the signals transmitted over optical or coaxial S/PDIF connectors—both carry exactly the same information. Selection of one over the other rests mainly on the availability of appropriate connectors on the chosen equipment and the preference and convenience of the user. Connections longer than 6 meters or so, or those requiring tight bends, should use coaxial cable, since the high light signal attenuation of TOSLINK cables limits its effective range.

A TRS connector (tip, ring, sleeve) also called an audio jack, phone plug, jack plug, stereo plug, mini-jack, or mini-stereo.

A DIN connector is a connector that was originally standardized by the Deutsches Institut für Normung (DIN).

The BNC (Bayonet Neill Concelman) connector is a very common type of RF connector used for terminating coaxial cable.

TOSLINK or Optical Cable is a standardized optical fiber connection system.

The XLR connector is an electrical connector design. XLR plugs and sockets are used mostly in professional audio and video electronics cabling applications.

The Mini-DIN connectors are a family of multi-pin electrical connectors used in a variety of applications. Mini-DIN is similar to the larger, older DIN connector. Both are standards of the Deutsches Institut für Normung, the German standards body.

The D-subminiature or D-sub is a common type of electrical connector used particularly in computers. Calling them "subminiature" was appropriate when they were first introduced, but today they are among the largest common connectors used in computers.

Video In Video Out, usually seen as the acronym VIVO (commonly pronounced vee-voh), is a graphics card port which enables some video cards to have bidirectional (input and output) video transfer through a Mini-DIN, usually of the 9-pin variety, and a specialised splitter cable (which can sometimes also transfer sound).

VIVO is found predominantly on high-end ATI video cards, although a few high-end NVIDIA video cards also have this port. VIVO on these graphics cards typically supports Composite, S-Video, and Component as outputs, and composite and S-Video as inputs. Many other video cards only support component and/or S-Video outputs to complement Video Graphics Array or DVI, typically using a component breakout cable and an S-Video cable.

The Digital Visual Interface (DVI) is a video interface standard designed to maximize the visual quality of digital display devices such as flat panel LCD computer displays and digital projectors. It is designed for carrying uncompressed digital video data to a display.

The connector also includes provision for a second data link for high resolution displays, though many devices do not implement this. In those that do, the connector is sometimes referred to as DVI-DL (dual link).

An RCA jack, also referred to as a phono connector or Cinch connector.

High-Definition Multimedia Interface (HDMI) is a compact audio/video standard for transmitting uncompressed digital data.

There are three HDMI connector types. Type A and Type B where defined since the HDMI 1.0 specification. Type C was defined since the HDMI 1.3 specification.

Type A is electrically compatible with single link DVI-D. Type B is electrically compatible with dual link DVI-D but has not yet been used in any products.

DisplayPort is a digital display interface standard (approved May 2006, current version 1.1a approved on January 11, 2008). It defines a new license-free, royalty-free, digital audio/video interconnect, intended to be used primarily between a computer and its display monitor, or a computer and a home-theater system.

The video signal is not compatible with DVI or HDMI, but a DisplayPort connector can pass these signals through. DisplayPort is a competitor to the HDMI connector, the de facto digital connection for high-definition consumer electronics devices.

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Audio Video Standard

Audio Video Standard, or AVS, is a compression codec for digital audio and video, and is competing with H.264/AAC to potentially replace MPEG-2. Chinese companies own 90% of AVS patents. The audio and video files have an .avs extension as a container format.

Development of AVS was initiated by the government of the People's Republic of China. Commercial success of the AVS standard would not only reduce China's royalty/licensing payments to foreign companies, it would presumably earn China's electronics industry recognition among the more established industries of the developed world, where China is still seen as an outlet for mass production with limited indigenous design capability.

In January 2005, the AVS workgroup submitted their draft report to the Information Industry Department (IID). On March 30, 2005, the first trial by the IID approved the video portion of the draft standard for a public showing time.

The dominant audio/video compression codecs, MPEG and VCEG, enjoy widespread use in consumer digital media devices, such as DVD players. Their usage requires Chinese manufacturers to pay substantial royalty fees to the mostly-foreign companies that hold patents on technology in those standards. For example, as of 2006, licenses ranging from $2.50 to $4 already make up about ten percent of the cost for a contract-manufactured DVD player unit.

According to the state-run media, a key consideration of AVS was to reduce foreign dependence on core intellectual properties used in digital media technology. Proposed as a national standard in 2004, AVS had a targeted royalty of 1 RMB (or about $0.10 USD) per player. On 30 April 2005, AVS standard video officially passed the public show and became the national standard.

AVS is currently expected to be approved for the Chinese high-definition successor to the Enhanced Versatile Disc.

Open source implementations of an AVS video decoder can be found in the OpenAVS project and within the libavcodec library. The latter is integrated in some free video players like MPlayer, VLC or xine. xAVS is also an open source AVS encoder with a working decoder.

China's proposed high-definition video disc format, known as CBHD (China Blue High-Definition), will include support for AVS.

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Audio Video Interleave

Audio Video Interleave, known by its acronym AVI, is a multimedia container format introduced by Microsoft in November 1992 as part of its Video for Windows technology. AVI files can contain both audio and video data in a file container that allows synchronous audio-with-video playback. Like the DVD video format, AVI files support multiple streaming audio and video, although these features are seldom used. Most AVI files also use the file format extensions developed by the Matrox OpenDML group in February 1996. These files are supported by Microsoft, and are unofficially called "AVI 2.0".

AVI is a derivative of the Resource Interchange File Format (RIFF), which divides a file's data into blocks, or "chunks." Each "chunk" is identified by a FourCC tag. An AVI file takes the form of a single chunk in a RIFF formatted file, which is then subdivided into two mandatory "chunks" and one optional "chunk".

The first sub-chunk is identified by the "hdrl" tag. This sub-chunk is the file header and contains metadata about the video, such as its width, height and frame rate. The second sub-chunk is identified by the "movi" tag. This chunk contains the actual audio/visual data that make up the AVI movie. The third optional sub-chunk is identified by the "idx1" tag which indexes the offsets of the data chunks within the file.

By way of the RIFF format, the audio/visual data contained in the "movi" chunk can be encoded or decoded by software called a codec, which is an abbreviation for (en)coder/decoder. Upon creation of the file, the codec translates between raw data and the (compressed) data format used inside the chunk. An AVI file may carry audio/visual data inside the chunks in virtually any compression scheme, including Full Frame (Uncompressed), Intel Real Time (Indeo), Cinepak, Motion JPEG, Editable MPEG, VDOWave, ClearVideo / RealVideo, QPEG, and MPEG-4 Video.

There is slight overhead when used with popular MPEG-4 codecs (Xvid and DivX, for example), increasing file size more than necessary. The AVI container has no native support for modern MPEG-4 features like B-Frames. Hacks are sometimes used to enable modern MPEG-4 features and subtitles, however, this is the source of playback incompatibilities.

AVI files do not contain pixel aspect ratio information. Microsoft confirms that "many players, including Windows Media Player, render all AVI files with square pixels. Therefore, the frame appears stretched or squeezed horizontally when the file is played back." There are other video container formats that allow irregular shaped pixels.

More modern container formats (such as QuickTime, Matroska, Ogg and MP4) offer more flexibility, however, the age of the AVI format, being widely supported on a vast range of operating systems and devices, and the availability of video editing and playback software like VirtualDub and Windows Media Player help keep the AVI file format popular amongst amateur videographers. To improve interoperability with the widest possible audience, videographers commonly install DirectShow filters like ffdshow to augment DirectShow, using AVI as a common-ground, lowest-common-denominator format.

Projects based on the FFmpeg project, including ffdshow, MPlayer, xine, and VLC media player, have solved most problems with viewing AVI format video files.

In June 2005, DivX, Inc. released its own container format called DivX Media Format (.divx extension) to succeed the AVI + DivX combo. However, this format is basically an enhanced AVI format (based on the same RIFF structure, for backward compatibility with existing players and devices) and so far, has gained no perceivable consumer traction, even where the DivX codec was once popular (the Xvid codec has instead become the codec of choice among most of the file-sharing groups ).

Type 1 is the newer of the two types. Microsoft made the "type" designations, and decided to name their older Video for Windows-compatible version "Type 2". In the late 1990s through early 2000s, most professional-level DV software, including non-linear editing programs, only supported Type 1. One notable exception was Adobe Premiere, which only supported Type 2. High-end FireWire camcorders usually captured to Type 1 only, while consumer level camcorders usually captured to Type 2 only. Software is available for converting Type 1 DV AVI files to Type 2, and vice-versa.

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SCART

SCART 20050724 002.jpg

SCART (from Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs, Radio and Television Receiver Manufacturer's Association) is a French-originated standard and associated 21-pin connector for connecting audio-visual (AV) equipment together. It is also known as Péritel (especially in France, where the term SCART is practically unknown), 21-pin EuroSCART (Sharp's marketing term for an attempt to market the connector in the Asian region) and Euroconnector.

In Europe, SCART is the most common method of connecting audio-visual equipment together, and has become a standard connector for such devices (even more so than the phono plug), however it is far less common elsewhere in the world.

The official standard for SCART is CENELEC document number EN 50049-1. SCART is sometimes referred to as the IEC 933-1 standard.

In America, another name for SCART is EIA Multiport, an EIA interface.

The SCART connector first appeared on television sets in 1977. It became compulsory on all new television sets sold in France starting from January 1980.

Before SCART came, consumer TV sets did not offer a standardized way of inputting signals other than RF antenna ones, and even antenna connectors differed between countries. Assuming other connectors even existed, devices made by different companies could have different and incompatible standards. For example, a domestic VCR could output a composite video signal through a German-originated DIN-style connector, an American-originated RCA connector, an SO239 connector, or a BNC connector.

The SCART system was intended to simplify connecting audio-video equipment (including TVs, VCRs, DVD players and game consoles). To achieve this it gathered all of the analogue signal connections into a single cable with a unique connector that made incorrect connections nearly impossible.

The signals carried by SCART include both composite and RGB (with composite synchronisation) video, stereo audio input/output and digital signalling. The standard was extended at the end of the 1980s to support the new S-Video signals. In addition, a TV can be awakened from standby mode or switched to video mode through a SCART connector.

SCART is bi-directional regarding standard composite video and analog audio. A television set will typically send the antenna audio and video signals to the SCART sockets all the time and watch for returned signals, to display and reproduce them instead. This allows "transparent" set-top boxes, without any tuner, which just "hook" and pre-process the television signals. This feature is used for analog Pay TV like Canal Plus and was in the past used for decoding teletext.

VCR will typically have two SCART sockets, one connecting to the television set ("up", "primary" or "1"), and another one for the set-top box or other devices ("down", "secondary" or "2"). When idle or powered off, the VCR will forward the signals from the television set to the set-top decoder and send the processed result back to the television set. When a scrambled show is recorded, the VCR will drive the set-top box from its own tuner and send the unscrambled signals to the television set for viewing or simple recording control purposes. Alternatively, the VCR could use the signals from the television set, in which case it would be inadvisable to change channels on the television set during the recording.

The "down" socket can also be used to connect other devices, such as DVD players or game consoles. As long as all devices have at least one "up" and "down" socket, this allows for connecting a virtually unlimited number of devices to a single SCART socket on the TV set. While Audio and Video signals can travel both "up" to the TV set and "down" to devices farther away from the TV, this is not true for RGB (and non-standard YPRPB) signals, which can only travel towards the TV set.

As the pins for Audio and (Composite) Video use the same pins on "up" and "down" connectors (and require a crosslinked cable), it is also possible to connect two devices directly to each other without paying attention to the type of the socket.

However, this no longer works when S-Video signals are used. As straight links (RGB Red and Blue up) were re-purposed to carry chrominance information, the S-Video pinouts are different for "up" and "down" SCART connectors. Further, they are often not fully implemented.

SCART also enables a device to command the television set to very quickly switch between signals, in order to create overlays in the image. In order to implement captioning or subtitles, a SCART set-top box does not have to process and send back a complete new video signal, which would require full decoding and re-encoding of the color information, a signal-degrading and costly process, especially given the presence of different standards in Europe. The box can instead ask the television set to stop displaying the normal signal and display a signal it generates internally for selected image areas, with pixel-level granularity. This can also be driven by the use of a "transparent" color in a teletext page.

SCART allows a connected device to bring it in and out of standby mode or to switch it to the AV channel. A VCR or other playback device will optimally power on when a cassette is inserted, power on the television set (or switch it to video mode) and then start playing immediately if the cassette's write protection tab is absent. When turned off, the VCR will ask the television set to power off as well, which the set will do if it had been powered on by the VCR's request and if it remained in video mode all along. Only some TV sets will do this—most only implement automatic switching to and from the SCART input.

The same signal can be used by a satellite receiver or set top box to signal a VCR that it is supposed to start and stop recording ("pin 8 recording"). This configuation usually requires that the VCR be farther from the TV set than the source, so the signal usually travels "down".

In the first case, the widescreen pin allows to indicate the current signal format, which allows widescreen sets to adjust the image width, and widescreen-capable standard sets to compress the image vertically. In the second case, the widescreen SCART signal is never active and the signal source performs the adaptations itself so that the image has always a standard format as a result. In practice, some sources will assume that the television set is always capable of widescreen functionality and hence never perform the adaptations. Some source will not even issue the widescreen signal or maintain it at the same level all the time. Other sources might offer the option of truncating the sides, but not of letterboxing, which requires significantly more processing. Notably, the circuitry of the early widescreen MAC standard decoders (eg. the Visiopass) could not letterbox. The limitations apply mostly to satellite television receivers, while DVD players can always at least letterbox and often zoom.

The use of the data pins was not standardised in the original SCART specification, resulting in the use of several different protocols, both proprietary protocols and semi-proprietary protocols based on standards such as D²B.

Some of the most creative usages appeared in analog satellite receivers. The function of decoding hybrid, time-compressed analog-digital MAC transmissions into RGB and analog audio was akin to making a digital receiver out of an analog one. The D²B pins (10 and 12) were used for communicating with satellite dish positioners and for driving magnetic polarizers, before these became incorporated into LNBs. The daisy-chaining features were used to connect both a Pay TV decoder and a dish positioner/polarizer to a single Decoder socket on the receiver.

CENELEC EN 50157-1 introduced AV.link as a standardised protocol to carry advanced control information between devices. It is a single-wire serial data bus and allows carrying remote control information and to negotiate analogue signal types (e.g. RGB). AV.link is also known as nexTViewLink or under different trade names such as SmartLink, Q-Link, EasyLink, etc. It appears as the Consumer Electronics Control channel in HDMI.

The original SCART specification provided for different cable (cordset) types denoted by a key colour. However, colour coding is rarely used in practice and cables often use different, non-standard configurations.

1 depends on protocol used.

Nearly all DVD players with SCART sockets output RGB video, which offers far superior picture quality to typical composite signals. However, many players do not have RGB output turned on by default but composite video—this often has to be set manually in the player's setup menu or via switches on the back of the player.

The Nintendo GameCube, Nintendo Wii, Sega Dreamcast, Sony PlayStation 2, Sony Playstation 3, Microsoft Xbox and Microsoft Xbox 360 can output RGB, YPbPr, S-Video, or composite video. These consoles, except for the Dreamcast which came standard with an RGB SCART cable, come with the standard composite video connector, but the manufacturers and third parties sell connectors for component video hookup and for RGB SCART hookup. Where the GameCube and Xbox automatically switch to the proper mode, the PlayStation 2 must be told via a selection in the system menu whether it is to use YPbPr or RGB component video. Also, some versions of legacy consoles such as Nintendo's SNES and Nintendo 64 (some, modified NTSC models only) are capable of outputting RGB signals (using the same cable as the GameCube).

Many older home computers (Amstrad CPC, later ZX Spectrum models, Commodore Amiga, Atari ST, BBC Micro and Acorn Archimedes, etc.) output RGB with composite sync suitable for SCART use, but most used varying non-standard DIN plugs. Standard-resolution arcade monitors use RGB signals with a composite sync, which is SCART-compatible.

Maximum SCART cable length is estimated to be about 10 to 15 metres without relay.

Due to the relatively high voltage used in SCART, "hot plugging" (connecting or disconnecting devices while they are on) is not recommended. Although there is no risk of personal injury, there is the possibility of damaging electronics within the devices if the connector is inserted improperly.

Quality differences exist in SCART cables. While a proper SCART cable uses miniature coax cables for the video signals, cheap SCART cables often use plain wires for all signals, resulting in a loss of image quality and greatly reducing the maximum cable length. A common problem is that a TV outputs a composite video signal from its internal tuner, and this is induced or cross-talked onto an incoming video signal due to inadequate or non-existent screening on a cheap SCART cable; the result is ghostly images or shimmering superimposed on the incoming signal. To non-destructively verify if a SCART cable uses coax cables, one can unscrew the strain relief at the SCART connector and fold open the plastic shell.

Using higher-quality cables such as those with ribbon cords that have properly shielded coax cables inside might help in reducing a 'ghosting' effect, but it doesn't always completely eliminate it due to various factors. A more permanent method is to remove pin 19 from the SCART plug that is put into the TV. Pin 19 is Video Out, and removing it prevents a signal from being broadcast by the TV into the cable in the first place, so it cannot cross-talk with the incoming signal. Cheaper SCART plugs can sometimes have the pins pushed inside the connector housing so as to remove it in a non-destructive manner (and thus allowing for its replacement in the future should the need arise by simply unscrewing the housing and pushing the pin back through its hole), though sometimes the pins are fixed in place on the inside by glue or rubber and can only be removed by forcefully twisting them off entirely. Generally though, for a standalone TV there is no need for video output on the TV end of the SCART plug, so in the majority of cases removing it completely should not be a problem. Whichever way it is done, however, once it is the SCART is rendered incapable of transmitting a video signal from that end of the cable, so it would be wise to mark it as such for future reference.

Gold-plated SCART connectors, which do not corrode and deliver a cleaner signal, might be preferable, although they always cost more than nickel ones. However, gold-plated connectors only give better performance when both plug and socket are gold plated. Gold and nickel are galvanically very different metals, and although inserting a gold-plated plug into a nickel plated socket may make a small difference at first, any atmospheric moisture that is present near the connector will cause an electrolytic reaction between the dissimilar metals. This will result in the nickel-plated connector corroding much more rapidly than it would if both connectors were nickel-plated. Dissimilar metals can also create a diode effect and lead to non linearities causing signal distortion. For good long-term connection quality it is always better to use matching connector materials.

Two pins provide switching signals.

Pin 8, the switch signal pin, carries a low frequency (less than 50 Hz) signal from the source that indicates the type of video present.

Pin 16, the blanking signal pin, carries a signal from the source that indicates that the signal is either RGB or composite.

The original specification defined pin 16 as a high frequency (up to 3 MHz) signal that blanked the composite video. The RGB inputs were always active and the signal 'punches holes' in the composite video. This could be used to overlay subtitles from an external Teletext decoder.

There is no switching signal to indicate S-Video. Some TVs can auto-detect the presence of the S-Video signal but more commonly the S-Video input needs to be manually selected.

The cables for connecting equipment together have a male plug at each end. Some of the wires such as ground, data, switching and RGB connect to the identical pin number at each end. Others such as audio and video are swapped so that an output signal at one end of the cable connects to an input signal at the other end. The complete list of wires that are swapped is: pins 1 and 2, pins 3 and 6, pins 17 and 18, pins 19 and 20.

SCART leads are available to buy in a wide range of stores in Europe and in specialized stores in North America.

In America, SCART cables and ports are also called EIA Multiport connectors/connections.

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RCA connector

The back of an RCA AM radio from the 1940s with RCA connector for adding a turntable. Tag around connector reads "An inexpensive RCA Victor record player will make a fine Victrola of this radio. Plug here."

An RCA jack, also referred to as a phono connector or Cinch connector, is a type of electrical connector that is commonly used in the audio/video market. The name "RCA" derives from the Radio Corporation of America, which introduced the design by the early 1940s to allow mono phonograph players to be connected to amplifiers.

For many other applications it began to replace the older jack plugs used in the audio world when component high fidelity started becoming popular in the 1950s.

The corresponding plug is called an RCA plug or a phono plug. The latter is often confused with a phone plug which refers to a jack plug or TRS connector.

In the most normal usage, cables have a standard plug on each end, consisting of a central male connector, surrounded by a ring. The ring is often segmented for flexibility. Devices mount the jack, consisting of a central hole with a ring of metal around it. The ring is slightly smaller in diameter and longer than the ring on the plug, allowing the plug's ring to fit tightly over it. The jack has a small area between the outer and inner rings which is filled with an insulator, typically plastic (very early versions, or those made for use as RF connectors used ceramic).

As with many other connectors, the RCA has been adopted for other uses than originally intended, including as a power connector, an RF connector, and as a connector for loudspeaker cables. Its use as a connector for composite video signals is extremely common, but provides poor impedance matching. RCA connectors and cable are also commonly used to carry S/PDIF-formatted digital audio, with plugs colored orange to differentiate them from other typical connections.

Connections are made by pushing the cable's plug into the female jack on the device. The signal-carrying pin protrudes from the plug, and often comes into contact with the socket before the grounded rings meet, resulting in loud hum or buzz if the audio components are powered while making connections. Continuous noise can occur if the plug partially falls out of the jack, breaking ground connection but not the signal. Some variants of the plug, especially cheaper versions, also give very poor grip and contact between the ground sheaths due to their lack of flexibility.

They are often color-coded, yellow for composite video, red for the right channel, and white or black for the left channel of stereo audio. This trio (or pair) of jacks can be found on the back of almost all audio and video equipment. At least one set is usually found on the front panel of modern TV sets, to facilitate connection of camcorders (through 3.5mm Jack to 3 RCA, also called Mini RCA plug), digital cameras, and video gaming consoles. Although nearly all audio-visual connectors, including audio, composite and component video, and S/PDIF audio can use identical 75 Ω cables, sales of special-purpose cables for each use have proliferated. Varying cable quality means that a cheap line-level audio cable might not successfully transfer component video or digital audio signals due to impedance mismatch and poor shielding quality (causing signal-to-noise ratio to be too low). Cables should meet the S/PDIF specification as defined by the international standard IEC 60958-3 for assured performance.

One problem with the RCA jack system is that each signal requires its own plug. Even the simple case of attaching a cassette deck may need four of them, two for stereo input, two for stereo output. In any common setup this quickly leads to a mess of cables, which is made worse if one considers more complex signals like component video (a total of three for video and two for analog audio or one for digital coaxial audio).

There have been numerous attempts to introduce combined audio/video connectors for direct signals, but in the analog realm none of these have ever become universal, except in Europe where the SCART connector is very successful. For a time the 5-pin DIN plug was popular for bi-directional stereo connection between A/V equipment, but it has been entirely displaced on modern consumer devices. Though RF modulators inherently transmit combined A/V signals in video applications, they depend on broadcast television systems and RF connectors which are not universal worldwide; RF signals are also generally inferior to direct signals due to protocol conversion and the RF limitations of the three major analog TV systems (NTSC, PAL and SECAM).

Nearly all modern TV sets, VCRs, and DVD players sold in Europe have SCART connectors, though sometimes supplemented by RCA and/or RF connectors and there are also SCART-RCA adaptors. Outside Europe, separate RCA connectors are the norm, supplemented by RF connectors for backward compatibility and simplicity; though mini-DIN connectors are sometimes used for S-Video connections, composite video, component video, and analog audio (mono or stereo) all use RCA connectors unless RF is used. In the digital realm, however, combined A/V connectors are gaining ground; HDMI is commonly being used today, and DisplayPort is a potential competitor to HDMI.

For audio signals, an RCA connection is called unbalanced, and a true balanced connection is generally preferred in certain applications because it allows for the use of long cables while reducing susceptibility to external noise.

The word phono in phono connector is an abbreviation of the word phonograph, because this connector was originally created to allow the connection of a phonograph turntable to a radio receiver, utilizing the radio as an amplifier. This setup was present in most radios manufactured in the 1930s onward by the Radio Corporation of America (RCA), who later marketed a special turntable for 45 RPM records (see photo).

Plugs and sockets on consumer equipment are conventionally color-coded to aid correct connections. The standard colors for the various signals are shown below.

In stereo audio applications there are combinations of either Black+Red or White+Red RCA connectors; in both cases, Red denotes Right. White or Purple may also be replaced by Black.

While these are the standard colours found on commercially made products, same-coloured cables may also be used. For example, a red cable may be used instead of a yellow one, as there is no other significant difference between them.

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Source : Wikipedia