Asynchronous Serial Interface (ASI) is a streaming data format which often carries an MPEG Transport Stream (MPEG-TS). The throughput of the interface is 216Mbps and utilises a BNC connector, to which a co-axial cable with 75 ohm impedance is attached. ASI interfaces are commonly found on broadcast quality equipment where there is a need to pass an entire multiple program transport stream (MPTS) to another device.
A Conditional Access Module (CAM) is a PCMCIA card that can decrypt DVB content that has been encrypted. The CAM will support at least one encryption system (eg. Mediaguard) and will have a limitation on the number of services that can be decrypted simultaneously. Aston CAMs are available for Mediaguard, Irdeto, Viaccess and Conax systems and the consumer version can decrypt two channels simultaneously whereas the professional version can decrypt up to twelve. The viewing card or smartcard from the content provider is inserted into the CAM and holds the keys for the services that it is permitted to decrypt.
RGB is a component video format in which the red, green and blue components are transmitted separately. However, the term “component video” is more usually used to refer to the analogue formats YUV or YPbPr. The Y component is the luminance (brightness) and also carries the sync pulses. The other two components represent the colour information as two colour difference channels; blue minus luminance (U or Pb) and red minus luminance (V or Pr). This is a way of encoding RGB signal information and the RGB information is reconstituted in the display device. YUV, YPbPr or ‘component’ connections can be found on many devices, both consumer and professional. On consumer devices the interface is typically three RCA (phono) sockets that are colour coded green (Y), blue (U or Pb) and red (V or Pr) whereas professional devices are more likely to have three BNC connectors. Sometimes YCbCr is shown next to analogue component connections instead of YPbPr, but this is technically incorrect as YCbCr actually refers to digital component signals (used internally within equipment). YUV and YPbPr analogue component signals can be used for both SD and HD video and these connections are commonly found on displays for analogue HD video, whilst HDMI is the commonly used connection for digital HD video.
Composite video is an analogue video format in which the luminance (brightness), chrominance (colour information) and sync are combined onto a single cable. The interface is typically a yellow colour coded RCA (phono) socket although this format can also be carried over SCART. Composite is the most common video interface and as such has interoperability benefits but is poorer in quality than S-Video, RGB or Component. Composite video is sometimes labelled or referred to as CVBS. Composite video is SD and can be in PAL, SECAM or NTSC format.
Digital Video Broadcast – Satellite (DVB-S) is a standard for broadcasting digital satellite television. The video, audio and data that comprise several channels are multiplexed into a single multiple program transport stream (MPTS) which is then transmitted on a satellite transponder. DVB-S uses QPSK modulation whereas DVB-S2 uses 8PSK modulation, increasing the bandwidth that can be used. DVB-S2 tends to be used where the content is HD as the extra bandwidth is useful for the high bitrate HD content and both HD and DVB-S2 typically require a change in reception hardware making it convenient to implement both at the same time. A DVB-S2 tuner can receive DVB-S content and so DVB-S2 will supersede DVB-S.
Digital Video Broadcast – Terrestrial (DVB-T) is a standard for broadcasting digital terrestrial television. The video, audio and data that comprise several channels are multiplexed into a single multiple program transport stream (MPTS) which is then transmitted on a UHF radio frequency using COFDM modulation.
An Electronic Program Guide (EPG) is an on-screen listing of channels and the programming that is being broadcast on those channels currently and in the near future.
A Graphical User Interface (GUI) uses images and visual indicators to interact with users as opposed to textual commands. Non expert users find GUIs easier to use and more aesthetically pleasing.
High Definition (HD)
High Definition (HD) refers to the resolution of the images that make up the video content. 1280 x 720p, 1920 x 1080i and 1920 x 1080p are all high definition resolutions, so called because the images contain more detail or ‘definition’ than the smaller standard definition resolutions. The letters indicate whether the video is interlaced (i) or progressive (p)
High Definition Multimedia Interface (HDMI) is an AV interface for transmitting uncompressed digital data. It is an alternative to consumer analogue standards such as composite, S-Video, RGBS, RGBHV/VGA and component video. If the content is digital, using an HDMI connection eliminates the need to convert it to an analogue format in order to pass it to a TV and therefore quality is retained. The HDMI connection can support SD or HD video as well as up to 8 channels of audio and CEC control. HDMI is electrically compatible with DVI-D. Content can be encrypted using HDCP on an HDMI connection to control reception of the content.
Internet Protocol Television, or IPTV, refers to television that is distributed over an IP network—the same kind of network people use to surf the internet and exchange emails.
There are various typs of IPTV. Building IPTV technology enables an organisation’s IP network to carry much more than just television. With IPTV, it's easy to distribute terrestrial and satellite television and radio, videos/DVDs, digital videos on-demand (VoDs), digital signage, information boards, and web content throughout a facility. All of this multimedia content can be viewed on standard and high definition TVs and various kinds of AV display equipment, as well as PCs on every desktop.
RGBS (also RGsB, RGBHV)
RGB is an additive colour model in which a colour is achieved by mixing quantities of Red, Green and Blue (primary colours). When referring to RGB as a video format, it is an analogue format in which the three discrete colour components are sent on three separate cables. RGB requires sync and this is where several types of RGB vary. RGBHV uses five conductors/cables, three for the colour components and two for sync (horizontal sync and vertical sync). This form is used for VGA and DVI-A and therefore is commonly found on PCs and on TVs marked ‘PC input’. RGBS uses four conductors/cables, three for the colour components and one for combined horizontal and vertical sync. Many devices send composite video on the sync as opposed to just the sync pulses. This type of RGB is common on consumer devices (DVD players etc.) and is the type of RGB used over a SCART connection. RGsB has the sync combined onto the same conductor/cable as the green colour component and is often called “Sync on Green”. It therefore only uses three conductors/cables. It is typically found on professional devices using BNC connectors as opposed to consumer devices which tend to be RGBS over SCART or RCA/phono sockets.
RGB is superior in quality to Composite and S-video formats and can technically be referred to as component video, however the term “Component video” is widely accepted to refer to a different format and so is not used for RGB.
S-Video is an analogue video format in which the luminance (brightness) and chrominance (colour information) are carried on separate conductors (within a cable), making it superior in quality to composite video but still inferior to component video as all of the colour information is still combined. The connector is a 4-pin mini-DIN socket, where the pins are luminance (Y), Chrominance (C) and the ground pins for each. S-Video is often labelled or referred to as Y/C and is SD in PAL, SECAM or NTSC formats.
Standard Definition (SD) refers to the resolution of the images that make up the video content. PAL and SECAM systems use a resolution of 720 x 576i whereas NTSC uses 720 x 480i. The ‘i’ indicates that the video is interlaced.
Serial Digital Interface (SDI) is an interface for broadcast quality digital video. The video is uncompressed and may run up to 270Mbps. Up to eight pairs of audio channels may be embedded within the SDI. The physical interface is a BNC connector, to which a co-axial cable with a 75 ohm impedance is attached. SDI interfaces are commonly found on broadcast quality video equipment.
The small form-factor pluggable (SFP) is a plug-in module used to support additional interface types such as Optical SDI input and ST-2022-6 or ST 2110 inputs. It can also be used as an output to provide a loop through function.
A Set-top Box (STB) is a hardware device that converts an external signal into a form that can be passed to a television.