Safe area The area of picture into which it is considered safe to place material, graphics, text or action, so that it will be viewable when received at home. Initially this was necessary with 4:3 aspect ratio screens as they were always overscanned to avoid showing the black that surrounds the active picture. Typically 5% in from the edges was considered safe. More recently the whole Safe Area issue has become far more complicated as there are both 4:3 and 16:9 displays, as well as 4:3, 16:9 and sometimes 14:9 (a compromised version of 16:9 that is more acceptable to those viewing on, generally analog, 4:3 screens) aspect ratios for program output. The transition to HD, always 16:9, ensures safe areas will need careful attention for many years yet. See also: Aspect ratio (of pictures)
SAIT-2 Super Advanced Intelligent Tape format that uses a 12.7mm (half-inch) wide tape and a helical scan format. It is designed for the general data storage market and is also used for the archive and transfer of file-based media data. SAIT-2 tape has a native capacity of 1 TB and a transfer rate of 60 MB/s, offering lossless compressed storage of 2.6 TB and transfer of 144 MB/s. There is a roadmap for SAIT-3 and SAIT-4 that speculatively predicts doubling of performance for each generation, projected for completion by 2010.
Sampling standard A standard for sampling analog waveforms to convert them into digital data. The official sampling standard for 625/50 and 525/60 television is ITU-R BT.601. ITU-R BT.709 and SMPTE 274M specify sampling for HD formats. They are generally written as the number of pixels per line x number of lines per frame/vertical refresh rate (in Hz) progressive or interlaced (P or I). For example: 1920 x 1080/50I. Sometimes the pixel count of the lines is omitted (but understood), making the example 1080/50I.
SAN Storage Area Networks are a well-established method of providing shared video storage and can offer platform-independent storage that may be accessed from, say, both Windows and Linux workstations. They allow applications direct access to shared storage by cutting out the usual client- server 'middle men' to provide improved workflow and better work sharing on a common store. See also: FAN, Fibre Channel, NAS Website: www.snia.org
SATA Serial ATA (Advanced Technology Attachment) is designed to transfer data between disks drives (hard and optical) and computer hardware and is the successor of ATA. SATA adapters and devices communicate over a high- speed serial link originally specified in SATA I at 1.5 Gb/s, now SATA II at 3 Gb/s and SATA III at 6 Gb/s is planned. The serial interface means the connector is smaller (than ATA) and can run faster - as fast parallel data starts to suffer from skewing - serial does not. SATA does not just serialize ATA. SATA II adds native command queuing, originally a feature of SCSI, that allows handling multiple pending transactions rather than just one at a time. This allows the disk to organize the transactions for faster operation. Website: www.sata-io.org
Scaling Analog video signals have to be scaled prior to digitizing in an ADC so that the full amplitude of the signal makes best use of the available levels, or numbers, in the digital system. The ITU-R BT.601 digital coding standard specifies, when using 10 bits, black to be set at level 64 and white at 940. The same range of values is ascribed should RGB be used. Computer applications tend to operate with a different scaling with black set to level 0 and white at 1023. For color they usually use RGB from 0-1023. However, most still keep to 8-bit accuracy so the scale runs from 0-255. Clearly, going between computers and TV requires processing to change color space and scaling. See also: Into digits (Tutorial 1)
Schema A collection of tables and constraints that describe the structure of a database. It provides a level of security as no one else can interpret the stored database without the schema; it is just a collection of figures. It organizes the database to allow scalability for expansion and defines efficient operation to suit a particular application.
Scrub (audio) Replay of audio tracks at a speed and pitch corresponding to jog speed - as heard with analog audio tape 'scrubbing' backwards and forwards past an audio replay head. This feature, which is natural for analog fixed- head recorders, may be provided on a digital system recording on disks to help set up cues.
SCSI The Small Computer Systems Interface is a high data rate, general-purpose parallel interface introduced in 1979 allowing up to eight devices to be connected to one bus (now 16 for Wide SCSI). Since then SCSI has hugely increased in performance but is now used mainly on high- performance workstations and RAIDs on servers while other lower cost interfaces such as USB2 and IEEE1394 connect external devices and SATA is used for hard disks. See also: Disk drives
SD, SDHC See SDTV, Secure Data
SDI See Serial Digital Interface
SDK Software Developers Kit. Typically a software and documentation package to facilitate the development of applications to run on a given operating system or other application. It provides another layer on top of an API, often including shortcuts and pre-built routines to make development easier and final operation faster.
SDTI Serial Digital Transport Interface (SMPTE 305M). Based on SDI, this provides realtime streaming transfers. It does not define the format of the signals carried but brings the possibility to create a number of packetized data formats for broadcast use. There are direct mappings for SDTI to carry Sony SX, HDCAM, DV-DIFF (DVCAM, DVCPRO 25/50, Digital-S) and MPEG TS.
SDTV Standard Definition Television. Digital television systems that operate using standard definition video formats, i.e. 720 x 460/60I or 720 x 567/50I. In both these may carry 4:3 or 16:9 images, and in all cases, the pixels are not square. All HDTV digital standards describe square pixels.
Secondary color correction Primary color correction, or grading, is applied to the whole image. Secondary correction is applied only to selected areas of the image - the area being defined by a pattern generator (e.g. a circle or rectangle), by curved lines or derived from the object itself using chromakey techniques - or any combination of all these. This way, for example, the color of a car in a clip could be changed from say, red to green.
Secure Data A non-volatile memory card format that is widely used in portable devices, including digital cameras, handheld computers, PDAs, GPSs. The latest cards, from 2 GB up, are SDHC (high capacity) Minimum writing speed is shown as Class 2, 4 or 6 offering 2, 4 or 6 MB/s. As development of these devices continues so the applications widen. See also: Flash memory, ING, P2, RAM Website: www.sdcard.org
SED Surface-conduction Electron-emitter Display technology is a mix of old and new, coupling Cathode Ray Tube (CRT) and LCD technologies. SED screens comprise thousands, even millions, of minute electron emitters - hence the CRT connection. The screens are thinner LCD displays and observers think SED technology is superior to current LCD and plasma monitors. Deliveries are slated to start in 2008 but may be delayed, and will concentrate on the bigger-screen end of the market - around 55-inches, initially.
Seek time (a.k.a. Positioning time) The time taken for the read/write heads of a disk drive to be positioned over a required track. Average seek time is the time to reach any track from the center track. Maximum seek/ positioning time is the time to reach any track from any track. A high performance modern hard disk offers around 4 ms average seek time and typically twice that for the maximum. Minimum seek time to adjacent tracks is as low as 0.2 ms for read, 0.4 ms for write. These times are critical to disk performance, especially when operating with the very high data rates associated with video and digital film. See: Disk drives, FrameMagic
Serial Digital Interface (SDI) Serial Digital Interface carries uncompressed digital video, multiple tracks of embedded audio and ancillary data over the ubiquitous 75-ohm coax cable, terminated in a BNC connector. As the demands of television have grown so has SDI. Today there are three types. SDI SMPTE 259M - for SD 4:2:2 digital television, is based on a 270 Mb/s transfer rate. This is a 10-bit, scrambled, polarity-independent interface, with common scrambling for both component ITU-R BT.601 and composite digital video and four groups each of four channels of embedded digital audio. Most broadcast digital equipment includes SDI which greatly simplifies its installation and signal distribution. It can transmit the signal over 200 meters (depending on cable type). HD-SDI Standardized in SMPTE 292M, this for 4:2:2 HD television. The serial bit- stream runs at 1.485 Gb/s to carry up to 10-bit Y,Cr,Cb component video as well as embedded audio and ancillary data. The interface is also specified for fiber for distances up to 2 km. 3G SDI (SMPTE 424M) operates at 2.97 Gb/s, twice the clock rate HD-SDI and is designed to carry high bandwidth HD television such as 1080/50P, 1080/60P, HD RGB, as well as 2K DI images. See also: Dual link, HSDL, Embedded audio
Server editing Video and audio editing that takes place within a server rather than in a workstation. See also: In-server editing
Server (file) A storage system that provides data files to all connected users of a local network. Typically the file server is a computer with large disk storage which is able to record or send files as requested by the other connected (client) computers - the file server often appearing as another disk on their systems. The data files are typically around a few kB in size and are expected to be delivered within moments of request.
Server (video) A storage system that provides audio and video storage for a network of clients. Those used in professional and broadcast applications are based on hard disk storage. Aside from those used for video on demand (VOD), video servers are applied in three areas of television operation: transmission, post production and news. Compared to general-purpose file servers, video servers must handle far more data, files are larger and must be continuously delivered. There is no general specification for video servers and so the performance between models varies greatly according to storage capacity, number of realtime video channels, protection level (RAID), compression codec and ratio, and speed of access to stored material - the latter having a profound influence. Store sizes are very large, typically from about 500 GB up to a few terabytes. Operation depends on connected devices: edit suites, automation systems, secondary servers, etc. The effectiveness of the server's remote control and video networking is vital to success.
Shannon Limit In 1948, C. E. Shannon's article 'The Mathematical Theory of Communication', established Information Theory which allows determination of the theoretical limit of any channel's information-carrying capacity. Information Theory made possible development of digital systems and without it, much of modern communications, including the Internet, would not exist. Only very recent technology has allowed operation close to the Shannon limit - V.34 33.6 kb/s phone modems are an example.
Signal-to-noise ratio (S/N or SNR) The ratio of noise to the wanted picture/signal information - usually expressed in dB. Noise can be high frequency - making pictures look grainy or adding hiss to sound. Digitally generated images or sounds are theoretically capable of being pure - noise-free - having an infinite signal to noise ratio. But for pictures, their purity may cause contouring artifacts if processed without special attention - a reason for Dynamic Rounding. A rule of thumb to express the realistic signal to noise capability of a digital system is given by the expression: S/N (dB) = 6N + 6 where N is the number of bits. See also: Contouring, Decibel, Dither, Dynamic Rounding, MPEG-2
Simulcasting The term used to describe the simultaneous transmission of a program over more than one channel: for example one analog PAL and another digital HD. Both versions are transmitted frame accurately at the same time to ensure that no viewer is disadvantaged.
Simultaneous true random access Describes access on a video server where each of its realtime video connections can access any sequence of stored frames regardless of the demands of othervideo connections. This implies there is no copying of material to achieve this. Such access makes control of video servers much more straightforward, and allows many independent operations to take place at the same time. See also: True random access
SMPTE Society of Motion Picture and Television Engineers. A United States organization, with international branches, which includes representatives of broadcasters, manufacturers and individuals working in the film and television industry. It has within its structure a number of committees that make recommendations (RP 125 for example) to the ITU-R and to ANSI in the USA. Website: www.smpte.org
SNMP Simple Network Management Protocol is the Internet standard protocol developed to manage nodes (servers, workstations, routers, switches, hubs, etc.) on IP networks. It enables network administrators to manage network performance, find and solve network problems, and plan for network growth. SNMP works by sending Protocol Data Units (PDUs) messages to different parts of a network. Agents, SNMP-compliant devices, store data about themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters.
Soft RAID A RAID system implemented by low level software in the host system instead of a dedicated RAID controller. While saving on hardware, operation consumes some of the host's power.
Square pixels See Aspect ratio - of pixels
SRAM See RAM
SRAM Static RAM memory chips in general behave like dynamic RAM (DRAM) except that static RAMs retain data in a six-transistor cell needing only power to operate (DRAMs require clocks as well). Because of this, current available capacity is lower than DRAM - and costs are higher, but speed is also greater. See also: Flash Memory
SSD See Flash Memory
Standard platform A computer and operating system built for general-purpose use. It cannot be used on its own but must be fitted with any, or many, of the very wide range of specific application software and additional hardware packages available. For example, the same standard platform may be used for accounting, word processing and graphics but each runs from a different software applications package and may need special hardware. The term has become somewhat confusing in that a standard platform canbe anything from a PC to a super computer. Also some applications are mutually exclusive - when the computer's hardware is configured for one it has to be re-configured to run another. It is then arguable whether this is still a standard platform or has it metamorphosed into a dedicated system?
Standards (television) A digital television standard defines the picture format (pixels per line and active lines), vertical refresh rate and whether the vertical scan is interlaced or progressive. For example, European SD digital television is 720 x 576/50I, and an HD standard is 1920 x 1080/30P. See also: Format (television)
Standards conversion Changing the standard of existing television material that may involve two processes (four if going from and to analog coded systems such as PAL and NTSC). The two main processes are format conversion to change the spatial (horizontal and vertical) sizes of the pictures and changing the vertical scan rate - the number of pictures per second. For broadcast applications this needs to be completed retaining the maximum possible fidelity of the input content. The re-sizing process involves the relatively straightforward task of spatial interpolation - spreading the information from the original pixel array over a different pixel structure. Note that the crude method of dropping or repeating lines/pixels will give very poor results and the detail of the interpolation process used is important for best results. The second process is more complex as, changing the number of frames or fields per second (temporal conversion) means creating new ones or removing some - preferably without upsetting any movement shown in the pictures, so simply repeating or dropping fields or frames will not do. For this the movement within the pictures has to be analyzed so that 'in-between' pictures can be synthesized. This is a very specialized area and there are highly developed techniques used on the best modern standards converters that do this very well, but never perfectly. See also: Format (conversion), Frame-rate conversion
Statistical multiplexing (a.k.a. Stat Mux) This increases the overall efficiency of a multi-channel digital television transmission multiplex by varying the bit-rate of each of its channels to take only that share of the total multiplex bit-rate it needs at any one time. The share apportioned to each channel is predicted statistically with reference to its current and recent-past demands. For example, football - generally with much action and detail (grass and crowds) - would use a higher data rate than a chat show with close-ups and far less movement. The data streams for each program are monitored and their bit rates varied accordingly to fit the bit rate of the whole multiplex. See also: Variable bit rate
Status M and Status A See: Densitometer
StEM Standard Evaluation Material was created by the ASC (American Society of Cinematographers) and DCI in 2004 to assess the quality of possible digital cinema compression systems and formats against the best that film can offer. It is about 25 minutes of material from multiple film formats.
Stereoscopic Window (Stereoscopic) The amount of stereo image available to the viewer is dictated by the frame surrounding a stereoscopic image, e.g. the size of TV or projection screen. This boundary is called the Stereo Window. Depending on their parallax objects will appear either in front, at or behind this window. IMAX has the largest window.
Stereoscopy The process of making and presenting images using 'left eye' and 'right eye' cameras. The resulting 'left eye' and 'right eye' stereo images allow audiences to perceive depth into and out of the screen. Although the technique can add greatly to the viewing experience and is often referred to as '3D', viewers cannot look around objects - as would be the case with real 3D. In stereoscopy, presenting objects from the left and right eyes' point of view in the same way that our eyes would look at them in the real world creates the depth effect. If the left and right eye images of an object are coincident at the screen, then it appears to be at the distance of the screen. If the left and right images on the screen are crossed over, with the right image on the left and the left image on the right, then the object appears to be in front of the screen as our eyes converge on the images. If the left and right images are not crossed over but closer together than the distance between our eyes (interocular distance generally taken as 63.5 mm for the average adult), then the object appears to be behind the screen as our eyes converge less. To show an object at infinity left and right images are shown spaced by the interocular distance. The advent of digital media replacements for film has sparked the development in new shooting technologies that can be capable of making live 3D TV. But generally post production is needed to correct unwanted differences between left and right cameras and to finesse the point of view and perspective. Now 3D cinema can be experienced at almost any digital cinema - not just at the big venues. A viewing system is required that can sequence the images into the correct eyes, such as Real D, Dolby or McNaughton. These require wearing glasses that are passive polarized (Real D), passive frequency based (Dolby) or active switched (McNaughton). Live shooting and easy exhibition means that live events can be shown on cinema screens - giving audiences a new experience and theatres a potential new revenue stream. For television, 3D screens have been developed but are now only just being mass-produced, partly due to the lack of 3D material! NHK Technical Services (NTS) has produced sets that use filters on the front of the screen and so can be watched without glasses. See also: 3D
Stop A ratio of amount of light where one stop represents a x2 change - doubling or halving of the amount of light. The operating range of film and electronic light sensors, such as CCDs and CMOS, are quoted in stops. Typically, a camera's shutter speed and the lens's aperture setting restrict the light arriving at the sensors/film so the mid brightness of the required scene corresponds to the middle of the sensor's or film's sensitivity range. Stops are simply the expression of a ratio, not absolute values. As they represent doubling or halving of light, they are actually powers of 2. So 1 stop = x 2   2 stops = x 4   3 stops = x 8   4 stops = x 16 etc.
Note that cine lenses are often marked in f-stops (white) and T-stops (red). The former is a geometric relationship between focal length and aperture and does not take into account how much light is lost within a lens. T-stops do and represent the real working values. So, on a lens that loses a full stop in transmission (i.e. a 50-percent loss), f/8 would result in the same exposure as T11. F and T values are usually close on prime lenses but zoom lenses show a greater difference.
Storage capacity (for video and film) This is just arithmetic. You can work all these figures out but it's really useful having some of the key numbers already to hand. Using the ITU-R BT.601 4:2:2 digital coding standard for SD, each picture occupies a large amount of storage space - especially when related to computer storage devices such as DRAM and disks. So much so that the numbers can become confusing unless a few benchmark statistics are remembered. Fortunately the units of mega, giga and tera make it easy to express the vast numbers involved. Storage capacities for SD video can all be worked out directly from the 601 standard. Bearing in mind that sync words and blanking can be re-generated and added at the output, only the active picture area need be stored on disks. In line with the modern trend of many disk drive manufacturers, kilobyte, megabyte and gigabyte are taken here to represent 103, and 109 respectively. Every line of a 625/50 or 525/60 TV picture has 720 luminance (Y) samples and 360 each of two chrominance samples (Cr and Cb), making a total of 1,440 samples per line.
625/50 format There are 576 active lines per picture creating 1440 x 576 = 829,440 pixels per picture. Sampled at 8 bits per pixel (10 bits can also be used) a picture is made up of 6,635,520 bits or 829,440 8-bit bytes - generally written as 830 kB. With 25 pictures a second there are 830 x 25 = 20,750 kbytes or 21 Mbytes per second.
525/60 format There are 480 active lines and so 1,440 x 480 = 691,200 pixels per picture. With each pixel sampled at 8-bit resolution this format creates 5,529,600 bits, or 691.2 kbytes per frame. At 30 frames per second this creates a total of 21,039 kbytes, or 20.7 Mbytes per second. Note that both 625 and 525 line systems require approximately the same amount of storage for a given time - 21 Mbytes for every second. To store one hour takes 76 Gbytes. Looked at another way each gigabyte (GB) of storage will hold 47 seconds of non-compressed video. 10-bit sampling uses 25% more storage. If compression is used, and assuming the sampling structure remains the same, simply divide the numbers by the compression ratio. For example, with 5:1 compression 1 GB will hold 47 x 5 = 235 seconds, and 1 hour takes 76/5 = 18 GB (approx). The storage requirement for VBR compression cannot be precisely calculated but there is usually some target average compression ratio or data rate figure quoted.
Mobile/Wireless/Web All media are limited by the bandwidth available in the transmission/ delivery channel. The most restricted cases are found in wireless and mobile applications where there are a variety of screen sizes, shapes and resolutions ranging from VGA PDAs (480x640) and some 3G phones with up to 320x240, or 176x144 pixels and frame rates down to 15Hz.
HD There are many video formats for HD but the 1080 x 1920 format is popular. Using 4:2:2 sampling, each line has 1920 Y samples and 960 each of Cr and Cb = 3840 samples per line. So each picture has 3840 x 1080 = 4.147 M samples. For 10-bit sampling each picture has the equivalent data of 5.18 M (8-bit) bytes. Assuming 30 pictures (60 fields) per second these produce 155 M bytes/s - 7.4 times that of SD. An hour of storage now needs to accommodate 560 GB.
2K and 4K 2K is a format used in digital film production that uses 4:4:4 10-bit sampling and RGB color space with an image size of 2048 x 1536, and has 24 frames per second. This makes one frame 11.80 MB, and an hour of storage 1.04TB. Note that applied to digital cinema exhibition, the 2K pixel size is 2048 x 1080, and the color space is X'Y'Z' and uses 12-bit 4:4:4 sampling, as defined by the DCI. The 4K image size is increasingly being used for digital movies. It is a x2 version of 2K, making x4 the pixel area. Here are some popular TV and digital film formats showing the volume of their uncompressed data. Compression of up to 100:1 is applied to MPEG-2 TV transmissions - over 100:1 may be used with more advanced codecs such as MPEG-4 and VC-1. DCI have given a maximum data rate for replay rate for digital cinemas of 250 Mb/s. Here JPEG 2000 compression is used and there is no inter-frame compression; this works out at a compression of about 6.4:1 for 2K and 25.5:1 for 4K. See also: Byte, ITU-R BT.601, ITU-R BT.709, SMPTE 272M
Streaming (video and/or audio) Refers to supplying a constant service, often realtime, of a medium. Although broadcast TV has done this from the beginning and SDI streams data, the term is one more usually associated with delivery by networks, including the Internet. The transmission comprises a stream of data packets which can be viewed/heard as they arrive though are often buffered, stored slightly in advance of viewing, to compensate for any short interruptions of delivery. For the Internet, media is usually highly compressed to offer acceptable results with 28 kb/s for audio and upwards of 64 kb/s for video. There are three predominant video streaming solutions: RealNetworks with RealVideo, RealAudio and RealPlayer, Microsoft Windows Media and Apple Quicktime - each with their particular advantages. As Internet transfers are not deterministic, pictures and sound may not always be constantly delivered. See also: File transfer, Isochronous
Structured Query Language (SQL) A popular language for computer database management. It is very widely used in client/server networks for PCs to access central databases and can be used with a variety of database management packages. It is data-independent and device-independent so users are not concerned with how the data is accessed. As increasing volumes of stored media content are accessible over networks, SQL is able to play a vital role in finding any required items.
Sub-pixel A spatial resolution smaller than that described by a pixel. Although digital images are composed of a matrix of pixels it can be very useful to resolve image detail to smaller than pixel size, i.e. sub-pixel. For example, the data for generating a smooth curve on the screen needs to be created to a finer accuracy than the pixel grid itself - otherwise the curve will look jagged. Again, when tracking an object in a scene, executing a DVE move, or calculating how a macroblock in MPEG-4 AVC coding moves from one picture to another, the size and position of the manipulated picture or element must be calculated, and the picture resolved, to a far finer accuracy than the that of whole pixels - otherwise the move will appear jerky or wrong. See also: Pixel, Tracking
Switch (network) Connecting network users via a switch means that each can be sending or receiving data at the same time with the full wire-speed of the network available. This is made possible by the aggregate capacity of the switch. So, for example, an eight-port Gigabit Ethernet switch will have an aggregate capacity of 8 Gb/s. This means many simultaneous high-speed transactions taking place without interruption from other users. The Internet is connected by thousands of very high speed network switches. See also: CSMA/CD, Hub
SXRD Silicon X-tal (crystal) Reflective Display, a reflective liquid crystal micro- display from Sony used in the first commercially available 4K-sized projectors. The display chip has 4096 x 2160 pixels on one-and-a-half inches of silicon. See also: Projectors (digital)
Synchronous (data transfer) This carries separate timing information (clock data) for keeping send and receive operations in step. The data bits are sent at a fixed rate so transfer times are guaranteed but transfers use more resources (than asynchronous) as they cannot be shared. Applications include native television connections, live video streaming and SDI. Operation depends on initial negotiation at send and receive ends but transfer is relatively fast. See: Asynchronous, Isochronous, SDI