Tag : Storage

Archive

Long-term storage of information. Pictures, sound and metadata stored in digital form can be archived and recovered without loss or distortion. The storage medium must be both reliable and stable and, as large quantities of information need to be stored, low cost is of major importance. Currently many are using magnetic tape. However there is also ongoing use of optical disks including DVD and Blu-Ray Disc formats and further developments are emerging.

Today, the increasingly IP and Ethernet-connected environments involving many video formats, including digital film, mean that data recorders make good sense. Archiving systems built around the current LTO-5 and LTO-6 data recorders are increasingly proving to be efficient and effective for media applications. The formats include backward compatibility to the previous LTO type. And with the tape cartridges offering 1.5 and 2.5 TB for LTO-5 and LTO-6 respectively, there is useful capacity.

Removable CD-size optical discs potentially offer quick access and denser storage as well as long-term reliability. The Archival Disc system, expected in 2015 from Sony and Panasonic, offers 300 GB with a roadmap to 1TB storage per disc.

For archiving stills and graphics there is far less need for of strong compression as the volume of data will typically be much smaller than that for video. CDs and DVDs are convenient and robust, giving near instant access to all stored pictures.

Traditionally, material is archived after its initial use – at the end of the process. More recently some archiving has moved to the beginning, or even before, the production process. An example is news where, in some cases, new material is archived as events happen. Later subsequent editing, etc., accesses this.

With the worldwide expansion of television channels everywhere, including online and mobile services, archives are increasingly used to help fulfill the huge demand for programming.

See also: AAF, Data recorders, LTO, Optical disks

Blu-ray Disc (BD)

This optical disk, designed for HD, can hold 25 GB on a single-layer CD-sized (12cm) disk using 405 nanometer blue-violet lasers. Dual layer disks hold up to 50 GB. Also available are triple layer (100 GB) and quadruple layer (128 GB) disks, which may accommodate 4K UHD video. The companies that established the basic specifications were: Hitachi Ltd., LG Electronics Inc., Matsushita Electric Industrial Co. Ltd., Pioneer Corporation, Royal Philips Electronics, Samsung Electronics Co. Ltd., Sharp Corporation, Sony Corporation, and Thomson Multimedia.

Players must be able to decode MPEG-2, H.264/AVC (MPEG-4 part 10) and SMPTE VC-1 coded material. MPEG-2 offers backward compatibility for DVDs while the other two more modern codecs are at least 50 percent more efficient, using less disk space or producing higher quality results. Audio codecs supported are Linear PCM, Dolby Digital, Dolby Digital Plus, Dolby TrueHD, DTS Digital Surround, DTS-HD.

The baseline data rate is 36 Mb/s – giving over one-and-a-half hours recording of HD material on a single layer, or about 13 hours of SD. For Blu-ray Disc movies (BD-ROM) the maximum transfer rate is 54 Mb/s for audio and video, with a maximum of 40 Mb/s for video. Random access allows easy video editing and simultaneous record and playback.

Ultra HD Blu-ray is the 4K Blu-ray format, expected for delivery Christmas 2015. Handling 4K UHD video at up to 60 f/s, the specification includes HEVC (H.265) video compression, a wider color gamut (than HD) as well as High Dynamic Range (HDR) and 10-bit video sampling. Disc capacities are set at 66 GB (dual layer) and 100 GB (triple layer). The system will also be able to play legacy standards including Blu-ray, DVD and CD. The final specification is expected in mid-2015.

See also: DVD, HD DVD, Optical disks, Professional Disc

Website: www.blu-raydisc.com

Cloud

For years computer network engineers have occasionally drawn a cloud in their diagrams – implying a distant reach of the network; usually somewhere where more storage can be accessed. Today, with reasonably high speed internet widely available, that fluffy thing has achieved front-of-stage importance with a rapid expansion of cloud computing service providers offering both storage and processing in their cloud. Or you can even have your own private cloud if you want.

Note that this is not a data center, requiring your computer to have the processing power and programs (apps) to alter and edit your video or audio. Cloud computing can be highly asymmetric – your computer only has to run a browser and upload video to the cloud, in theory all the rest could be done in the cloud – depending on the tools available and how you want to work.

Typically these clouds are accessed via the Internet and offer access to any amount of your uploaded data from any internet connection. There is a very wide range of services available, such as payrolls, tax returns, sales coordination, etc. Some providers offer specific services for the media industry, specializing in video storage, viewing and editing via their cloud. Uploading newly shot footage and editing can be done from anywhere with an internet connection. Once in the cloud, all those allowed to can access the footage by logging onto the website. This has major benefits for location shoots; not least being able to deliver valuable new footage to a safe place without moving. It also helps with studio productions as all required personnel can contribute to the production and post-production, without having to move from their laptop.

Technically cloud services divide into three recognized types:

Software as a Service (SaaS) is popular as it only requires a modest computer on the ground, which basically just has to support a web browser, because all the software and probably quite a bit of storage needed is in the cloud. So, for example, freshly shot video footage could be stored in the cloud. Then it could be, viewed, edited, and reviewed. Another powerful use is planning and organizing production, so everyone is kept up to date.

With Platform as a Service (PaaS) users can run their own applications, provided that it fits with what cloud service operators offer in terms of platforms. When using Infrastructure as a Service (IaaS) you can run whatever programs you like on the cloud’s available hardware

Consolidation

Clearing continuous space on a disk store to allow consistent recording. This generally involves the moving of data on the disks to one area, leaving the remainder free so that recording can proceed track-to-track – without having to make random accesses. The larger the amount of data stored, the longer consolidation may take. Careful consideration must be given to large-capacity multi-user systems, such as video servers, especially when used for transmission or on-air.

The need for consolidation arises because of the store’s inability to continuously record television frames randomly at video rate. This is taken care of by Quantel’s FrameMagic. Recording can take place over small, scattered areas of the store so there is no need for consolidation.

Consolidation

See also: Defragmentation, FrameMagic, True random access

COTS

Commercial off-the-shelf, usually referring to the use of common components from the computer market to create a product, or application. For instance COTS components and say, a Windows platform, can be used to make a channel-in-a-box integrated video playout system that replaces a host of dedicated hardware. Typically, to meet broadcasters’ expectations of reliability and performance, considerable attention to the precise choice of platform (not all computers are the same) along with considerable software development and testing is needed. The use of COTS in television and movie production is now commonplace. High end editing runs on COTS-based platforms, with the big development effort in software, not hardware!

DAM

Digital Asset Management is about managing and controlling the receiving, cataloging, storage, retrieval, distribution, archive and deletion or removal of digital assets. In the media world these assets are typically digital video, audio and images. DAM could help to access materials needed to make a new program. The program is then an asset in itself which can be handled by MAM – media asset management. With thousands of TV channels now broadcasting or narrow casting, TV programs made for one channel may well be useful to others.

DAS

Direct Attached Storage, typically on hard disks, is available only to a single user as opposed to NAS that can be available to everyone on the network. Typically this uses SCSI, SAS or Fibre Channel protocol and provides add-on storage for servers that maintain high data rate and fast access.

Data carousel

This is a file system that rotates and delivers its content into a network at a defined point in a cycle, for example, teletext pages. It is a method to make a large amount of information or data files available within a reasonably short time following a request. The data is inserted into the digital broadcast transport stream.

See also: IP over DVB

Data recorders

Machines designed to record and replay data. They usually include a high degree of error correction to ensure that the output data is absolutely correct and, due to their recording format, the data is not easily editable. These compare with digital video recorders which will conceal missing or incorrect data by repeating adjacent areas of picture, and which are designed to allow direct access to every frame for editing. Where data recorders are used for recording video there has to be an attendant ‘workstation’ to produce signals for video and audio monitoring, whereas VTRs produce the signals directly. Although many, but not all, data recorders are based on VTRs’ original designs, and vice versa, VTRs are more efficient for handling pictures and sound while data recorders are most appropriate for data. They are useful for archiving and, as they are format-independent, can be used in multi-format environments.

See also: LTO

DFS

Distributed File System. Used to build a hierarchical view of multiple file servers and shared files on a network. Instead of having to think of a specific machine name for each set of files, users only need to remember one name as the key to a list of shared files on multiple servers. DFS can route a client to the closest available file server and can also be installed on a cluster for even better performance and reliability. Medium-to-large sized organizations are most likely to benefit from using DFS while smaller ones should be fine with ordinary file servers.

Digital Asset Management (DAM)

Content is worthless if you cannot find it. If you can find it easily and have rights to use or sell it, it has value. The content will vary in size from a whole movie, to a few frames of news footage. Digital Asset Management (a.k.a. media asset management or digital asset warehousing) is about the storage and use of both digital content and its metadata. The latter comprises descriptions of the content, such as text and thumbnail images, stored in a database for easy searching and management. The metadata is linked to the content files, images or video to allow retrieval.

Digital disk recorder (DDR)

Computer disk systems that record digital video and generally intended as drop-in replacements for VTRs or as video caches to provide extra digital video sources for far less cost than a DVTR. They have the advantages of not requiring pre-rolls or spooling but they are not necessarily able to randomly access all video frames in realtime. DDRs can also offer the higher data rates needed for uncompressed recordings at an economic price, for SD as well as HD and 2K/4K (film) resolutions.

See also: Linear, True random access

DVD

Digital Versatile Disk (aka digital video disk) – invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995 as a high-density development of the compact disk. It is the same size as a CD, 12 cm diameter, but stores upwards of 4.38 GB of actual data (seven times CD capacity) on a single-sided, single-layer disk. DVDs can also be double-sided or dual-layer – storing even more data.

The capacities commonly available are:

DVD-5              Single-side, single-layer         4.7 GB
DVD-9              Single-side, dual-layer           8.5 – 8.7 GB
DVD-10            Double-sided, single-layer     9.4 GB
DVD-18            Double-sided, dual-layer       17.08 GB

DVD-5 and DVD-9 are widely used. However the double-sided disks are quite rare, partly because they are more difficult to make and they cannot carry a label.

There are various types of DVD including:

DVD-R – recordable DVDs with a data capacity of 4.38 GB are popular and low priced.

DVD+R – dual layer recordable DVDs with a total capacity of two DVD-Rs.

DVD-RAM – re-recordable DVD, re-use up to around 100,000 times. Capacity of 4.38 GB (single-sided). Some camcorders have use these – they offer instant access to shot material and record loop features – useful when waiting to record an event, like a goal, to happen. At home it can provide a removable media alternative. A particular feature is that it can record and replay at the same time.

DVD-Video – combines the DVD with MPEG-2 video compression, with multichannel audio, subtitles and copy protection capability.

To maximize quality and playing time DVD-Video uses variable bit rate (VBR) MPEG-2 coding where the bit rate varies with the demands of the material. Typically a 525/60 TV format, 24 f/s movie would use an average bit rate of 3.5 Mb/s, but for sections with a great deal of movement it could peak at 8 or 9 Mb/s. Only 24 f/s are coded onto the disk, the 3:2 pull-down conversion to 30 f/s taking place in the player. This allows a 120-minute 24 f/s movie to fit on a DVD-5. To store video (not film) with 50 or 60 discrete fields per second, the bit rate tends to average around 6 or 7 Mb/s, but again depends on the running time, original material and desired picture quality.

CBHD China Blue High-Definition or China High Definition DVD is a variant of HD DVD which is only used within China.

Multi-channel audio DVD-Video supports PCM, MPEG and Dolby Digital audio, for anything from mono, stereo, Dolby Surround to 5.1 channels. Digital Theatre Sound (DTS) and Sony Dynamic Digital Sound (SDDS) are options. Up to eight separate audio streams can be supported, allowing multiple languages, audio description, director’s commentary, etc. For example, a release may have 5.1 Dolby Digital English, two-channel Dolby Digital Spanish with Dolby Surround, and mono French.

Region coding Disks can be region-coded and so only play in a particular region (as defined in the player), a set of regions or be ‘code-free’.

The region numbers are:

  1. Canada, US, US Territories
  2. Japan, Europe, South Africa, Middle East (including Egypt)
  3. Southeast Asia, East Asia (including Hong Kong)
  4. Australia, New Zealand, Pacific Islands, Central America, South America, Caribbean
  5. Former Soviet Union, Indian Subcontinent, Africa (also North Korea, Mongolia)
  6. China

See also: HD DVD, Blu-ray Disc, Dolby Digital, Dolby Surround, MPEG-2, MPEG-4

DVTR

Digital Video Tape Recorder. Sony showed the first DVTR for commercial use in 1986, working to the ITU-R BT.601 component digital video standard and the associated D1 standard for DVTRs. It used 19 mm cassettes recording 34, 78 or (using thinner tape) 94 minutes of uncompressed video. Due to its relatively high cost, its use was somewhat limited to high-budget projects. Other formats, D2 and D3 that recorded digitized composite PAL and NTSC, offered lower cost solutions at the cost of price ‘coded’ quality.

Thomson’s VooDoo Media Recorder (designated as D6) was the last uncompressed digital videotape recording system.

All subsequent DVTRs record compressed component video. Provided there is no re-coding or transcoding, DVTRs do not suffer ‘generation loss’ due to re-recordings as tape noise, moiré, etc., and dropouts are mostly invisible due to sophisticated correction and concealment techniques. However tape is subject to wear and tear and the resulting errors and dropouts necessitate complex error concealment circuitry. In extreme cases multiple passes can introduce cumulative texturing or other artifacts.

Today, videotape is rarely used as hard disks and solid-state memory are widely used in acquisition, post production and program distribution. However much video archiving makes use of computer tape formats.

See also: Betacam SX, D5, D9, DV, DVCPRO, HDCAM, LTO

FAN

File Area Networks are a shared storage concept that stores shared files in multiple locations. However the user is not aware of where the files are located; they are simply accessed as if they were local or single site storage. The IT industry is actively pursuing this concept in order to provide organizations with strategically central data sources that are geographically agnostic, which can lead to considerable resource savings.

FANs also have potentially broad applications in post production and broadcast. It is not impossible to imagine a post house with a ‘front door’ in the city where clients can come and watch their job progress, driven by a creative at in his country retreat – perhaps with the storage itself in a third location. Broadcasters with multiple sites (perhaps local stations or subsidiaries) are also looking at FANs with great interest.

Website: http://en.wikipedia.org/wiki/File_Area_Network

Flash Memory

Non-volatile solid-state memory that offers fast write and read times, but not as fast as DRAM, and can withstand considerable shock (G-force). Generally known as CF (compact flash), it is popular storage on portable / hand-held devices including professional and consumer video and stills cameras. Also when packaged in a memory card or a ‘pen drive’ case, it is enormously durable, withstanding intense pressure, extremes of temperature and even water immersion.

There are many technologies applied to make CF cards and its development continues apace with increasing capacities: 2005 – 1GB, 2GB; 2006 – 4GB, 64GB, and later 128GB and 256GB (2010). Transfer rates are quoted in different ways. With the ‘x’ rating, multiples of the standard Compact Disk data transfer rate of 150kB/s (= x1) are shown. So a x600 memory card offers up to 90 MB/s – fast enough to record only slightly compressed HD. ‘Class’ is another rating, so Class 6 indicates a (minimum) transfer rate of 6 MB/s. UHS (Ultra High Speed – ) is a third speed rating system with UHS-1 supporting up to 104 MB/s.

In the professional market manufacturers tend to offer memory cards that bundle several CF chips to provide a particular high performance to match the needs of their products – typically high-end cameras and computers. Currently these offer in the order of up to a few TB storage. In 2010 Sandisk, Sony, and Nikon proposed developing a new 500 MB/s memory card with over 2TB capacity.

Flash memory is increasingly used to replace computer hard drives – with solid-state drives (SSD) – providing much higher speed of data transfers. Current offerings are up to 1 TB with faster read and write rates than disks, low power consumption and high robustness, these have many advantages. Cost prohibits a large-scale defection from the traditional rotating mass PC storage device – at the moment.

Hard disk drives

Hard disk drives (HDD) comprise an assembly stacking up to 12 (typically 5 or 7) rigid platters coated with magnetic oxide, each capable of storing data on both sides. Each recording surface has an associated read/write head, and any one may be activated at a given instant. Disk drives give rapid access to vast amounts of data, and are highly reliable as they have only two moving parts – the swinging head assembly and the spinning disk. They can be written and read millions of times. The use of disks to store audio, video and images has changed many aspects of digital production editing and transmission.

For high capacity, disks pack data very tightly indeed. Areal density, the amount of data stored per unit area of the disk surface, is one measure of their technology. Currently available high capacity drives from manufacturer Seagate achieve nearly 1 Tb/square inch in a 6 TB drive. Several new technologies are ready to boost the performance of future drives. These include filling the drive with Helium gas offering lower friction, so allowing more platters to be used in the same standard sized 3.5-inch case. Perpendicular magnetic recording (PMR – laying tracks under one another) is established technology. Upcoming techniques include shingled magnetic recording (SMR) and heat-assisted magnetic recording (HAMR). These create new spaces for yet greater capacities and performance of disk drives.

The rate of increase in capacity seems to have slowed in recent years which may mean that the currently used technology (PMR) is nearing its practical limit. For this performance the heads float only a few molecules off the disk surface, so that even minute imperfections in the surface can cause heating of the head assembly. As a result, high capacity disk drives have to be handled with great care, especially when running. Vibration could easily send heads off-track or crashing into the disk surface – possibly with terminal consequences.

Where will hard disk drives be in 10 years’ time? In 2000, when 50 GB was ‘high capacity’, the Digital Fact Book successfully predicted the arrival of 2TB drives in 2010. Now a new 10-year prediction is made. The long term historic HDD storage development doubles the capacity every two years (increasing 41%/year). In some years it has reached 60%, but the DFB believes progress is getting tougher and expects progress to be nearer 41%/year. Anyway, who wants a 660 TB HDD – perhaps someone working with 8K UHD at 120 f/s?

HDD capacity chart

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

See also: Areal Density, RAID, SCSI

Website: www.seagate.com

HD DVD

Designed as the successor to the standard DVD optical disk and principally supported by Toshiba, HD DVD could store about three times as much data as its predecessor; 15 GB single layer, 30 GB dual layer. Often called 3x DVD as it has three times the bandwidth (1x@36Mb/s and 2x@72Mb/s) and storage, it was discontinued in 2008, leaving just Sony’s Blu-ray Disc in the market.

See also: DVD, Optical disks

Website: www.dvdforum.org

HSM

Hierarchical Storage Management is a scheme responsible for the movement of files between archive and the other storage systems that make up hierarchical storage architecture. Typically there may be three layers of storage, online, near-line and offline, that make up the hierarchy that HSM manages. Managing these layers helps to run the archive and have the required speed of access to all stored material.

Latency (of data)

The delay between requesting and accessing data. For disk drives it refers to the delay due to disk rotation only, even though this is only one of several factors that determines time to access data from disks. The faster a disk spins the sooner it will be at the position where the required data is under the replay head. As disk diameters have decreased so rotational (spindle) speeds have tended to increase but there is still much variation. Modern 2.5-inch drives typically have spindle speeds of between 7,200 and 15,000 RPM, so one revolution is completed in 8 to 4 ms respectively. This is represented in the disk specification as average latency of 4 or 2 ms.

For solid-state ‘drives’ (SSD) the latency is much less resulting in faster access to data, particularly if the data is scattered around the store; here, SSD can be over 100 times faster than HDD, but just a few times faster for large unscattered data files.

LTO-5, LTO-6

Linear Tape-Open. An open magnetic tape data storage technology started in the late 1990s. The standard form factor is called ‘Ultrium’ and uses linear, not helical , recording. In 2000 an LTO-1 Ulitrium cartridge could store 100 GB. There is a development plan guided by the Linear Tape-Open (LTO) Program Technology Provider Companies HP, IBM and Quantum. In 2012 it reached LTO-6, offering 2.5 GB storage per cartridge, with a maximum data speed of 160 MB/s. There is also a lossless 2.5:1 LTO-DC data compression scheme available (not suitable for video). In the video industry LTO is used for video archive and transfer.

LTO-7 is immanent, offering 6.4 TB native capacity before using the 2.5:1 compression, and 315 MB/s maximum date speed. The LTO development plan continues, stretching to LTO-10.

See also: SAIT-2

Website: www.quantum.com

MAM

Media Asset Management is used in modern broadcast and post production that increasingly depends on file-based operation rather than the use of tape. MAM can track and manage all aspects of the use and repurposing of media assets so it is clear which assets have been used where. This can help both in technical operations such as adjusting an edit, as well as commercial requirements such as billing.

NAS

Network Attached Storage is a file server with an operating system that supports the popular file sharing protocols, such as CIFS (Windows) and NFS (Unix). It is accessed as a client on a network such as Ethernet. This is relatively low cost and easy to set up but it is limited by the constraints of the network. If the network is very busy, then access to the NAS will be slower. An alternative form of shared storage can be set up with a SAN that creates its own separate network.

See also: SAN

Optical disks

Disks that use optical techniques for recording and replay of material without the read/write heads touching the disk. These offer large storage capacities on ‘CD sized’ 5.25-inch (12 cm) polycarbonate disks with technologies including CD, DVD and Blu-ray Disc. These offer capacities of 700 MB for CD, 4.37- 15.90 GB for DVD and 25-128 GB for Blu-ray Disc. The CD format was designed for audio; DVD was designed for SD video and Blu-ray Disc for HD video. All have another life in data storage. They are all available in ROM and read/write forms. The next development is expected to be a disk able to store a 4K UHD movie, which will also be useful for storing large quantities of data.

See also: Blu-ray Disc, DVD, Professional Disc, XDCAM

PAM

Production Asset Management could be considered as a subset of MAM It is intended to co-ordinate the work of all stages involved with post production, and so ensure it runs efficiently and meets planned deadlines and budgets. It can enhance collaboration and manage down to a detailed level for edit suites and media storage, and manage those contributing other elements, such as special effects. Management of items such as the original video, audio, EDLs, proxies, versioning, content protection, backup, can be included. But PAM is not tightly defined and some say that it ends when the media file is ‘flattened’, with all the effects, corrections, cuts, mixes, etc, are applied and resolved to produce one layer of video and the finished tracks of audio.

Professional Disc (PFD)

Sony’s name for their Blue Laser disk technology used in XDCAM products and for data recording. This has many similarities to the Blu-ray disk, with CD/DVD dimensions it is housed in a cartridge, weighs 90g and offers 23.3 GB storage on one-side and a data rate of 9 MB/s (72 Mb/s). It can support 70 minutes of 50 Mb/s MPEG IMX and faster-than-realtime transfers. Good for around 10,000 re-record cycles it is more compact, faster and more versatile than tape.

Further development has produced a dual-layer model with 50 GB, then a triple with 100 GB and a quad version with 128 GB, providing up to four hours of recording.

See also: Optical disks

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

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

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

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.

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

WORM

Write Once/Read Many – describes storage devices on which data, once written, cannot be erased or re-written. This applies to some optical disks that are removable, making them useful for archiving. CD-R and DVD-R are examples.

See also: Optical disks