Category Archives: S

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 CRT screens as they were always overscanned to avoid showing the ‘black’ that surrounded the active picture. Typically 5% in from the edges was considered safe. Today most TV screens are flat panels, and the pictures are 16:9. There are controls for zooming or changing the aspect ratio, but usually all the active picture is displayed on the screen.

See also: Aspect ratio (of pictures)

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), e.g. 1920 x 1080/50I. Sometimes the pixel count of the lines is omitted (but understood), making the example 1080/50I.

SAN

Storage Area Network is a well-established method of providing shared video storage and can offer platform-independent storage that may be accessed from, say, Windows, Linux and Mac OS workstations. It allows 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.

SAN

The design recognizes that moving large amounts of data (video) is inconsistent with normal-network general-data traffic. Therefore it forms a separate network to connect data-hungry workstations to a large, fast array of disks. Although any network technology could be used, Fibre Channel predominates with current speeds of up to 14 Gb/s. SANs are scalable but additions may be complex to implement. Currently, expansion is ultimately limited by architecture and management considerations. However, in practice it can be difficult to sustain multiple high bandwidth (e.g. for HD or 4K) streams from a SAN. Quantel’s Genetic Engineering is designed to solve this problem and is capable of playing back multiple 2K and 4K streams simultaneously.

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, then SATA 2 at 3 Gb/s, SATA 3 at 6 Gb/s, and the latest SATA 3.2 offers a transport speed of 16 Gb/s.

The serial interface means the connector is smaller (than ATA) and can run faster, because fast parallel data starts to suffer from skewing with some channels of the parallel connection being faster/slower than others. Serial data cannot skew. SATA does not just serialize ATA. For example, SATA 2 added native command queueing, originally a feature of SCSI, that allows handling multiple pending transactions rather than just one at a time. Also disk drives can organize the transactions and so offer faster operation.

Website: www.sata-io.org

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. The schema 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 started as 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). This could comprise a controller and up to seven disks or devices of different sorts – hard disks, optical disks, tape drives, scanners, etc., and may be shared between several computers.

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, while SATA is used for many hard disks.

The original SCSI specified a cabling standard (50-way) that had to be kept short, a protocol for sending and receiving commands and their format. It is intended as a device-independent interface so the host computer needs no details about the peripherals it controls. SCSI’s continued development has resulted in ever faster data transfer rates. Currently 16GFC (Fibre Channel) has a maximum transfer rate of 1600 MB/s (12.6 Gb/s).

There are many other SCSI interfaces besides Fibre Channel. iSCSI (Internet Small Computer System Interface) can run over any physical transport capable of transporting Internet Protocol (IP). This gets much support as developments in Ethernet outpace those in FC. The performance of this though is network-dependent.

Serial SCSI using SSA (Serial Storage Architecture) FC-AL, IEEE1394, and Serial Attached SCSI (SAS), break away from the parallel cabling to offer data transfers currently up to 1200 MB/s. This is popular with many hard disk drives.

See also: Disk drives

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 the 270 Mb/s standard definition 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. There is also an HD version. Standardized as SMPTE 348M this provides a 1.5 Gb/s data link.

SDTV

Standard Definition Television. Digital television systems that operate using standard definition video formats, i.e. 720 x 480/59.94I or 720 x 576/50I. Both these may carry 4:3 or 16:9 images, and in all cases, the pixels are not square. All HDTV and UHDTV digital standards describe square pixels.

Second Screen

Using a tablet or smart phone to access more background information, or to add comments, about what you are watching on TV is said to be using a ‘second screen’. Some productions offer an app and access to more relevant material to add to the experience – beyond just the passive watching of TV.

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, while the rest of every image is unchanged.

Secure Digital (SD) Card

A non-volatile memory card format that is widely used in portable / hand-held devices, including digital cameras, tablet computers, smart phones, etc. SD cards are specified with speeds described in multiples of the standard CD data speed – 150 kB/s, and capacity.

The original SDSC (Standard Capacity) offer up to 2 GB storage and a bus speed of 25 MB/s. Next up SDHC (High Capacity) provides from 2 GB to 32 GB storage and support for FAT32 file systems (as is used on many PCs). SDXC introduced in 2009 supports capacities beyond 32 GB to 2TB and a maximum data speed of 300 MB/s. For yet more performance there is now Ultra Speed Bus. UHS-I can have a clock speed of 100 MHz, so handling 50 MB/s in 4-bit mode. UHS104 has a 208 MHz clock and can transfer 104 MB/s. UHS-II raises the transfer rates to a possible 156 MB/s (312 MB/s half duplex).

Currently the highest capacity on the market is a SDXC from SanDisk, offering 512 GB. This was introduced at the IBC 2014 trade show where many of the visitors and exhibitors are constantly seeking higher capacities and speeds to handle ever larger TV formats and higher frame rates.

Markings on the cards indicate their performance. A ‘C’ refers to a speed Class. The number in the big C is the minimum sustained transfer speed in MB/s; typically 2, 4, 6, 8, and 10 are used. Above that you will see a ‘U’ on the card. A ‘I’ in the U is for 10 MB/s UHS-I, and III for 30 MB/s.

SD cards have transformed video storage in both amateur and professional video cameras. Panasonic was an early adopter with its professional camcorders using P2 cards. Each card includes SD chips, a micro computer and RAID controller. There are no moving parts. There is no noise. It takes only tiny power and it is compact and robust – and a long way from tape and disk-based recording. P2 cards can read at 8x real-time for quick transfers to editing equipment. They can be used as edit stores in themselves.

See also: Flash memory, ING, P2, RAM

Website: aframe.com/blog, www.sdcard.org

SED

Surface-conduction Electron-emitter Display technology was gaining attention in the mid 2000’s. It is a mix of old and new, coupling Cathode Ray Tube (CRT) and LCD technologies. SED screens comprise millions of minute electron emitters – hence the CRT connection. The screens are thin and many thought the technology would take over a large part of the screen market. But it faded in 2009. All SED and done!

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. Many long seek times can degrade performance when using a fragmented disk, so slowing the access to data.

Solid State Drives also have seek times, and their performance can degrade with fragmentation. However SSD technology has very much lower seek times, and generally provides very speedy performance.

See: Disk drives, FrameMagic

Sequence Detection

This is the act of finding film frame boundaries. For “perfect” pSF or 2:3 sequences, this will produce a regular pattern of frames; for “non-perfect” sequences the pattern will not be regular and might have discontinuities at edit points for example.

Serial Digital Interface (SDI)

Serial Digital Interface carries uncompressed video, multiple tracks of embedded audio and ancillary data usually over the ubiquitous 75-ohm coax cable, terminated in a BNC connector. As the demands of television have grown so SDI has risen to the challenge to continue providing a reliable plug-and-play connection. Today there are many types to fit with the demands for bigger and faster video formats.

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 video equipment includes SDI which greatly simplifies its installation and signal distribution. It can transmit the signal up to 350 meters (depending on cable quality and connected equipment, specifically distribution amplifiers and routers).

HD-SDI is standardized in SMPTE 292M is 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.

6G-SDI (not yet standardized) operates at 5.94 Gb/s and can carry 4K at up to 30P.

12G-SDI (not yet standardized) operates at 11.88 Gb/s can carry 4K at up to 60P frame rate.

The higher bit rates can work over shorter lengths of coax and Fibre Optic versions can be used for the larger/faster frame-rate formats over longer distances.

See also: Dual link, Embedded audio, UHDTV, SDTV, SMPTE

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 operations: 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 large, typically from about 500 GB up to a many 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.

Signal-to-noise ratio (S/N or SNR)

The ratio of the wanted signal (image, sound…) information to noise, usually expressed in dB. Noise can be high frequency, making pictures look grainy or adding a 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 they are processed without enough care; 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. Hence an 8-bit system has 54 dB S/N and a 10-bit system 66 dB. This would be the noise level of continuous LSB dither and would only be produced over the whole picture by digitizing a flat field (i.e. the same gray over the whole picture) set at a level to lie midway between two LSBs. If it were set exactly on a digital level, there would be no noise. Other test methods give a variety of results, mostly producing higher S/N figures.

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 SD, one HD, a third on the Internet as well as services to mobile devices. All versions are transmitted at the same time but due to coding times and system latency they are unlikely to be synchronous.

Simultaneous true random access

Describes access on a video server where each of its realtime video connections clients access any sequence of stored frames regardless of the demands of other video connections. This implies there is no copying of material to achieve this. Such access makes operation and control of video servers much more straightforward, and allows many independent operations to take place at the same time even when using the same video.

See also: FrameMagic, True random access

Single-frequency Network (SFN)

A group of transmitters all working on the same frequency within range of each other. Usually these will interfere causing serious problems with reception. However with DVB-T2 transmission, and the TV channels all running on the same locked frequencies over all transmitters, any interference is constructive, adding to the quality of the received signal. SFN’s are very efficient with radio frequency spectrum use as, for example, all transmissions of a group of TV channels around a country can use the same channel frequency throughout a network. Also the constructive interference makes it easier to get good reception, sometimes even with a modest antenna.

Smart TV

A television set that includes an internet connection, some computing power and a UI to access the ‘Smart’ functions – including internet browsing. Popular uses include accessing ‘catch-up TV’ services such as Comcast’s Xfinity and the BBC’s iPlayer. Smart TVs now make up nearly 50 percent of the set population in the USA. However, the use of the internet beyond the catchup services is reported to be in decline, with the UI cited as a major cause.

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. Within its structure it has a number of committees that make recommendations (RP 125 for example) to the ITU-R and to ANSI in the USA.

Here are just a few of the many standards and recommendations issued by SMPTE:

259M SDI for 4:2:2 and 3fsc
272M AES/EBU audio and aux data into video ancillary space
292M HD-SDI
294M TV format, 720 x 483 at 59.94P Hz
305M SDTI Serial Data Transport Interface
424M 3 Gb/s signal/data serial interface

Website: www.smpte.org

Snell

Apt name for a world leader in broadcast technology with more than 40 years’ experience in providing digital technology to the media and broadcast industry. Today the Snell product range encompasses a comprehensive range of software and hardware solutions for the creation, management and distribution of content to today’s multi-screen world of tablets, televisions, mobiles and PCs. Snell is a Quantel company.

www.snellgroup.com

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.

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 available specific application software and additional hardware packages. 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 can be 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 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 while 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 far 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

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)

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

StEM

In 2004 the Standard Evaluation Material was created by the ASC (American Society of Cinematographers) and DCI to assess the quality of possible digital cinema picture compression systems and formats against the best that film can offer. It is about 25 minutes of material from multiple film formats. At that time the most widely used compression system for video was MPEG-2 and some said the StEM film was an ‘MPEG breaker’ with smoky scenes and movement that would challenge that compression system. The next year DCI recommended JPEG 2000, an entirely different compression system to the established DCT-based JPEG.

Stencil®

A keying signal used in graphics systems – such as the Quantel Paintbox that is built into all the company’s editing systems. It can be drawn, derived from picture information, or both. It can be used to define the area of an object, obscure part or all of an object, making it transparent or partially transparent, and used to control the application of paint… and more.

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. Stereo television and film can create a 3D illusion, but it not real 3D.

Stereoscopy

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.

HD video and DCI digital movies sparked development in new shooting technologies that can make 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. Exhibition become far easier with digital cinema were one projector can sequence left and right images replayed from one player. This removes the nightmare of aligning and keeping two projectors, and running two films in sync and registration; even then weave, scratches and sparkles can lower the quality of presentation. Now most cinemas are 3D-capable and have a viewing system to sequence the left and right images into 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 theaters a potential new revenue stream.

For television, 3D screens and viewing systems have been developed but usually require viewers to wear 3D glasses (active or passive depending on the system) to sequence the left and right images to the correct eyes. Probably the greatest domestic application has been for use in the virtual world of computer games.

See also: 3D

Websites: Dolby www.dolby.com/professional/motion_picture/solutions_d3ddc.html

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.

F stops are the simple calculation taking focal length and aperture into account. This does not fully solve the problem of how much light gets to the sensor/film when lenses are not 100% clear. The T stop takes the transmissive quality of the lens into account. The transmissive quality is affected by the glass used to make the lens and any additional anti-reflective and conditioning coatings applied to the lens elements.

For example:

Use the formula:-  T-stop = F-stop/transmission_fraction. Where transmission ranges from 0 (opaque) to 1 (perfectly clear)

For a perfect lens the calculation is T = F/1 ->  T == F

For a lens with 80% transmission (0.8) then T = F/0.8

So for an F stop setting of 4 the real measure of light getting to the sensor is equivalent to 4/0.8 = 5.0

Note that the depth of field will still be calculated from the F stop setting – only the exposure is set using the T stop.

Storage capacity (for video and movies)

This is just arithmetic. You can work all these figures out yourself 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; ‘one gig’ trips off the tongue far more easily than ‘one thousand million’ and sounds much less intimidating.

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, 106 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. There is a wide choice of services and screens. In the most restricted cases some wireless and mobile applications are supported with a variety of small screens, shapes and resolutions ranging from VGA (480×640) and some 3 or 4G phones with up to 320×240, or 176×144 pixels and frame rates down to 15Hz. Many modern smart phones boast 1920 x 1080 HD screens.

HD
There are many video formats for HD but the 1920 x 1080 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.

UHD
Ultra High Definition has two sizes of picture – 4K and 8K. 4K is 2160 x 3840 twice the length and breadth of 1080 HD. If using 4:2:2 10-bit sampling then each picture is 16.588 M samples, equivalent data of 20.735 MB. At 30 f/s that amounts to 622.05 MB/s, .2.24TB/h.

8K at 4320 x 7680 is twice the size, and four times the area of 4K. One frame is 66.355 Msamples, or 82.94 MB. At 30 f/s this produces 2.488 GB/s, making an hour nearly 9 TB of data.

2K and 4K DCI
2K is a format used in digital movie production that uses 4:4:4 10-bit sampling and RGB colorspace 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. It is a 2×2 version of 2K, making x4 the number of pixels.

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 in digital cinemas is 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.

Format (H x V)Sampling (MB)Image size Mb/sOne Frame (GB) Data rate  One Hour
320/15P4:1:1 8-bit320 x 2400.1214.46.5 (3G phone)
525/60I4:2:2 8-bit720 x 4800.6916676
625/50I4:2:2 8-bit 720 x 5760.8316676
720/60P4:2:2 10-bit1280 x 7202.31104500
1080/60I4:2:2 10-bit1920 x 10805.21248560
1080/25P4:4:4 10-bit1920 x 10807.81560700 (RGB)
1080/60P4:4:4 10-bit1920 x 10807.837441680 (RGB)
2K/24P4:4:4 12-bit2048 x 1080101913860 (DCI cinema)
2K/24P4:4:4 10-bit2048 x 15361223041036 (cine production)
4K/60P4:2:2 10-bit3840 x 2160 20.749762240 (4K UHD)
4K/24P4:4:4 12-bit4096 x 216039.876503442 (DCI cinema)
4K/24P4:4:4 10-bit4096 x 30724892164144 (cine production)
8K/60P4:2:2 10-bit 7680 x 432082.9199048960 (8K UHD)

See also: ByteInto digits (Tutorial 1), ITU-R BT.601, ITU-R BT.709, SMPTE 272M

Streaming (video and/or audio)

Refers to supplying a constant realtime media service. Although broadcast TV has done this from the beginning, and SDI streams data, the term is more usually associated with delivery by networks, usually the Internet where it accounts for a large majority of the traffic. 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/hearing, to compensate for any short interruptions of delivery. For the Internet, media is compressed and generally offers acceptable results for audio and 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 continuously delivered.

Many popular sites, such as YouTube and the BBC iPlayer, offer both SD and HD services. A few are working with 4K UHD. Most TV and radio stations offer live streaming services.

See also: IPTV, 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 one 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 or position, 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 object resolved, to a far finer accuracy than the that of whole pixels, otherwise the move will appear jerky or wrong.

Sub-pixel-animation
Moving an image with sub-pixel accuracy requires picture interpolation as its detail, that was originally placed on lines and pixels, now has to appear to be where none may have existed, e.g. between lines. The original picture has to be effectively rendered onto an intermediate pixel/line position. The example of moving a picture down a whole line is achieved relatively easily by re-addressing the lines of the output. But to move it by half a line requires both an address change and interpolation of the picture to take information from the adjacent lines and calculate new pixel values. Good DVEs and standards converters work to a grid many times finer than the line/pixel structure.

See also: Pixel, Tracking

Super Hi-Vision (SHV)

Also known as 8K UHD, pioneered by the Japanese broadcaster NHK this is a very large format television system with a pictures size of 7680 x 4320 pixels. It is proposed to run at frame rates from 23.98 to 120 Hz and start broadcasting by 2020. SHV can also support a 22.2 sound system with 22 speakers and two woofers.

See also: ITU-R BT.2020, UHD

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 (diagonal) of a silicon chip. The design maintains a uniform, ultra-thin liquid crystal cell gap without any spacers in the image area, contributing to contrast performance, claimed as 4000:1. Its Vertically Aligned Nematic (VAN) liquid crystal changes state fast enabling speeds up to 200 f/s while minimizing image smear. HDTV-sized SXRD chips have been used in Sony consumer products, including a front projector and rear projection televisions up to 70 inches.

See also: Projectors (digital)

Synchronization

Temporal conversion without the use of interpolation. If input and output field or frame rates are not identical then field or frame drops or repeats must occur.

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