Contact us Links
Below are the details of the various types of video signal

Digital

The Serial Digital Interface (SDI), standardized in ITU-R BT.656 and SMPTE 259M, is a digital video interface used for broadcast-grade video. A related standard, known as High Definition Serial Digital Interface (HD-SDI), is standardized in SMPTE 292M; this provides a nominal data rate of 1.485 Gbit/s. An emerging interface, commonly known in the industry as dual link and consisting essentially of a pair of SMPTE 292M links, is standardized in SMPTE 372M; this provides a nominal 2.970 Gbit/s interface used in applications (such as digital cinema) that require greater fidelity and resolution than standard HDTV can provide. A more recent interface, consisting of a single 2.97 Gbit/s serial link, is standardized in SMPTE 424M,
These standards are used for transmission of uncompressed, unencrypted digital television signals (optionally including audio) within television facilities; they can also be used for packetized data. They are designed for operation over short distances; due to their high bitrates they are inappropriate for long-distance transmission. SDI and HD-SDI are currently only available in professional video equipment; various licensing agreements, restricting the use of unencrypted digital interfaces to professional equipment, prohibit their use in consumer equipment. (There are various mod kits for existing DVD players and other devices, which allow a user to add a serial digital interface to these devices).

SDI is the best way to transmit digital video data. The Serial Digital Interface (SDI) standard is used by professional broadcast studios and video production centers (SMPTE259M standard interface). There is no hassle with silly encryption schemes, video/audio sync problems or incompatible standards. It is a straightforward unidirectional protocol over one coaxial wire. It is therefore preferable to other standards like firewire or DVI. Another advantage of SDI is that the decompressed digital video data is transmitted directly from a digital source, such as your DVD player or satellite receiver, into the scaler of your choice (such as the DVDO iScan HD with SDI input module). Your video signal remains unprocessed and in the digital domain, avoiding quality degrading digital-to-analog and analog-to-digital conversion steps, and thereby retaining the best possible picture clarity.

HDMI (High-Definition Multimedia Interface) is the first and only industry-supported, uncompressed, alldigital audio/video interface. By delivering crystal-clear, all-digital audio and video via a single cable, HDMI dramatically simplifies cabling and helps provide consumers with the highest-quality home theater experience. HDMI provides an interface between any audio/video source, such as a set-top box, DVD player, or A/V receiver and an audio and/or video monitor, such as a digital television (DTV), over a single cable. HDMI supports standard, enhanced, or high-definition video, plus multi-channel digital audio on a single cable. It transmits all ATSC HDTV standards and supports 8-channel, 192kHz, uncompressed digital audio and all currently-available compressed formats (such as Dolby Digital and DTS), HDMI 1.3 adds additional support for new lossless digital audio formats Dolby TrueHD and DTS-HD with bandwidth to spare to accommodate future enhancements and requirements. HDMI is the de facto standard digital interface for HD and the consumer electronics market: More than 400 companies have become adopters, and more than 60 million devices featuring HDMI are expected to ship in 2006 (conservative estimate by In-Stat). Convergence – HDMI is the interface for convergence of PC and consumer electronics devices: HDMI enables PCs to deliver premium media content including high definition movies and multi-channel audio formats. HDMI is the only interface enabling connections to both HDTVs and digital PC monitors implementing the DVI and HDMI standards. Evolving standard – HDMI is continually evolving to meet the needs of the market. : Products implementing new versions of the HDMI specification will continue to be fully backward compatible with earlier HDMI products.

Analogue Video

RGB stands for Red Green and Blue, these are the 3 colours are the primary colours of light so it is no suprise that it is also used to display a TV picture. Using RGB the picture is sent as three separate colours corresponding to the three colours used in a TV to display the picture. A high resolution RGB picture can have a bandwidth of over 10MHz and this is without doubt the best way to send analogue picture information to a TV or display the best alternative is digital (SDI or HDMI). Component video Component video is comprised of a Y signal (this is the luminance being a mixture of red, green and blue), and two colour difference signals, referred to as either V & U or Cr & Cb respectively. Both require a sync signal to generate the required timing inside the TV so that a viewable picture can be built up. When using a DVD player it may be better to use Y Cr Cb output , as they generate these straight from the digital signals. There are more than a few options for sending the sync signal with RGB. The norm is for 75R terminated signals and 0.7V peak with higher voltage producing a brighter image. If you need to get RGB to more than one display simultaneously then a distribution amplifier with a bandwidth of 50MHz is suitable
A composite video signal is where all the colours and luminance information along with the necessary timing signals are all squeezed (or encoded) into one combined signal. Inevitably there is some loss and compromise involved with this process. This manifests itself as a lack of detail in the picture and a general blurring compared with the original RGB signals. In the UK the system of encoding used is PAL with NTSC used in the states. It is PAL encoding that is responsible for the moiré patterning sometimes seen on newsreaders suits or check shirts etc. Composite video is the yellow single phono connection on your VCR or TV and is the usual method used in a scart connection. Composite video uses a 75R cable for connection. A composite signal is decoded in your TV set to recover the original RGB signals and timing information. Typical bandwidth of a composite video signal is only a couple of MHz. In the UK the Luminance or brightness information is derived from the RGB signal and then the colour is added to this at a frequency of 4.43MHz. This inevitably limits the available bandwidth to considerably less than 4.43MHz. A similar system is used in the USA but the colour here is at 3.58MHz. See the section on converting NTSC to PAL for more detail but it is the different colour frequencies that gives rise to the problem of black and white picture when an NTSC video is played on some compatible VCR's
Component video comprises three separate signals. One of these conveys the luminance information, and the other two convey information of the colour content of a picture. Like RGB is can produce an extremely high quality picture. The Y or luminance signal contains the main picture information and a combined 0.3V sync the other 2 signals contain the colour difference information. If you remove the sync from the equation then there is a relatively simple mathematical relationship between component video and RGB. The different flavours of component video simply differ slightly in the relative amounts of each signal. As most digital sources use the Y Cr Cb format this is the one most commonly found on consumer equipment and the one supported by the Keene Electronics Compnent2RGB convertor. The Y, Cr, Cb system is the CCIR 601 standard adopted for most digital video applications. The traditional YUV is more often found on analogue professional equipment. Rather perversely the Y Cr Cb system adopted for digital video encoding is sometimes referred to as CAV or Consumer Analogue Video. There is some confusion over the exact meaning of YCrCb and YPrPb. This seems to have come about because one school of thought (English) refers to YCrCb as an analogue signal and YPrPb as its digital equivalent. Another school of thought (This time American) suggests that YCrCb is interlaced and YPrPb is progressive. (As we are a British company we favour the British version!). When buying component video equipment it is very important to make sure you get the right flavour of component for the equipment you are using. If you for example want to connect to a plasma display then nearly all of these use Y Pr Pb and connecting with YUV will produce a heavily tinted picture. YUV = Y B-Y R-Y
Y C or S video or SVHS is one step up from composite video. It is found more often these days and definitely does produce a higher quality of picture than composite. The black and white or Luminance (Y) portion of the signal is sent separately form the colour or chroma (C) portion. This does avoid the nasty moiré patterning and give improved detail when compared with composite video. S video typically uses a four pin mini din connector but can be frequently found on scart connectors. Because the same pin (15) on the scart plug is for the colour as both input and output the socket cannot be bi-directional and must be configured as either an input or output. Adaptors are available to convert from S video to composite and visa versa but these do not restore the lost picture detail.