Digital Video Part 2

7/28/2019 Digital Video Part 2

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JULY 2004www.securitysales.com A1

Part 2 of 4

Presented by Brought to You by


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nyone who has lived at the same location for more than five years can relate

to this statement: Too much stuff and not enough room. This holds true for

video as well.

Welcome to the second chapter in the four-part Digital Video for D.U.M.I.E.S. series (see

page A2 of the March issue for Part 1 of the series, Essentials of Digital Video Compression).

D.U.M.I.E.S. stands for dealers, users, managers, installers, engineers and salespeople.

This installment, brought to you by Honeywell, explains the different methods of stor-

ing digital information and explores emerging authentication techniques.

How to Calculate the File Size of an Image

Even when compressed, a video signal requires a fairly large amount of storage space.

The term relating to the amount of storage is known as the image file size. The file size is

the amount of storage required for one single image of video. File sizes may range from

500 bytes to more than 30 kilobytes (KB) for a single image.

The following information is used to calculate the size of one image of uncompressed video:

Number of horizontal pixels (width)

Number of vertical rows (vertical)

Bit depth (8 bit, 16 bit, etc.)

Image file size = (pixel width X pixel rows X bit depth) / 8* / 1,024**

* - represents an 8-bit byte

** - equals the number of bytes per kilobyte

Accurately capturing clear

digital video images is only

half the battle.Effectively

managing and safeguarding

those images for future

viewing requires selecting

storage media optimallysuited for the application.

Essentials of

DIGITAL

VIDEO

STORAGE

www.securitysales.com JULY 2004A2

Part 2of 4

By Bob Wimmer

Video Security Consultants

[email protected]

AT A GLANCE

Video images require a lot of stor-

age space

Image size = pixel width

X pixel rows X bit depth

/ 8 / 1,024

Primary storage media are digital

audiotape, digital linear tape, digital

versatile disc and hard drive disk

Random arrays of independent

disks guard against lost data

IP-based systems use network at-

tached storage and storage area

networks

A


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As an example, let us calculate the

file size of a 640 X 480 image with a

24-bit depth:

640 X 480 X 24 = 7,372,800/ 8 = 921,600

/ 1024 = 900K

Lets go one step further and deter-

mine the amount of storage for this

example for just 1 second, which con-

sists of 30 images:

1 second of uncompressed video =

900K X 30

Storage required = 27MB /second

This example surely explains the need

for video compression as explored in

Part 1 of this series. With that explained,we can now move on to the many differ-

ent forms of storage incorporated

throughout the industry. (Note: The list-

ing is alphanumerical and does not in-

dicate the authors choice or preference.)

DAT Provides High Capacity

Digital audiotape (DAT) was originally

conceived as a CD-quality audio format.

In 1998, Sony defined the Digital Data

Storage (DDS) standard, transforming

the format into one that could also beused for digital video and data storage.

DAT technology uses a 4mm tape

that incorporates a technique called

helical scan recording(a method of

reading/writing data to tape via a rotat-

ing head/drum assembly). This is the

same form of recording method used

in standard videocassette recorders.

For this reason, it is generally only used

in environments where high capacity is

the primary requirement.

The tape in a helical scan system is

pulled from a two-reel cartridge and

wrapped halfway around a cylindrical

drum containing two read heads andtwo write heads, arranged alternately.

The read heads verify the data written

by the write heads. The cylinder head

is tilted slightly in relation to the tape,

and spins at 2,000 rpm. Short diago-

nal tracks are written across the width

of the tape, about eight-times longer

than the width, and contain about

128KB of data with error correction.

DAT tapes are available in two for-

mats: DDS and DataDAT. The DDS

protocol is the most common, and is

represented by several standards, all

of which are backward compatible.

DAT is often used for archiving or

backing up data with storage capacity

of up to 40GB. However, because of

the wide wrap angle of the tape and

the consequent degree of physical

contact, both the head and the media

are prone to wear and tear.

Linear Tape Is Cost-Effective

Developed by Digital Equipment

Corp. (DEC), digital linear tape (DLT)uses the sa me basic for mat as DAT,

except the tape is 1/2-inch wide and

the DLT drives offer a faster data

transfer rate than other tape drive

achieving rates of 2.5MBps.

Today, we have the next generation of

technology known as super digital lin-

ear tape (SDLT). With storage up 160GB

(320 compressed) and data transferspeed in the 16MBps range, this form of

storage offers an extremely cost-effec-

tive method for archiving large amounts

of data for extended periods of time.

DVDs Are More Durable Than Tape

A digital versatile disc (DVD) is sim-

ilar to a CD, but has a much larger

data capacity. A standard DVD holds

about seven-times more data than a

CD. Like a CD, the data on a DVD is

encoded in the form of small pits and

bumps in the tracks of the disc.

A DVD consists of several layers of

plastic, totaling about 1.2mm thick.

Each layer is created by injection

molding polycarbonate plastic. This

process forms a disc that has micro-

scopic bumps arranged as a single,

continuous and extremely long spiral

track of data.

For the most part, DVRs incorporat-

ing DVD storage technology use MPEG-

2 compression. At the present time,

double-sided, double-layered DVDsoffer 16 to 18GB of storage per disc.

Head rotation (2,000 rpm)

Write BVerify B

Write A

Tape

Verify A

Data recorded in angled strips across tape

How a Helical Scan System Works

DAT technology uses a 4mm tape that incorporates a technique called helical scanrecording (a method of reading/writing data to tape via a rotating head/drum assembly).This is the same form of recording method used in standard videocassette recorders.

Single-sided, single-layered (~5GB)

Single-sided, double-layered (~9GB)

Double-sided, double-layered (~18GB)

Layered DVD Technologyand Storage Capacities

For the most part, DVRs incorporatingDVD storage technology use MPEG-2compression. At the present time, dou-

ble-sided, double-layered DVDs offer 16to 18GB of storage per disc.


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The advantages of DVDs are that

they are not prone to the wear and

tape noise that sometimes affects DAT

and DLT storage units. However, they

are limited in the amount of storage

available per disc.

Hard Drives Combine Best Aspects

One of the most popular forms of

storage media is the hard disk drive

(HDD). The advantages of HDD com-pared to tape can be explained with a

few basic statements.

First, with a tape, you have to fast-

forward or reverse to get to any partic-

ular point on the tape, which can take

several minutes of time. On a hard

disk, you can move to any point on the

surface of the disk almost instantly.

In a tape storage unit, the head as-

sembly is always in contact with the

actual tape media. Hard drives, on the

other hand, never actually touch the

storage media. This prevents the wear

and tear that normally is common-

place in all tape storage devices.

Finally, information on a hard disk

is stored in extremely small magnetic

packets of information compared to

tapes. The size of these packets is

made possible by the precision of the

platter and the speed of the medium

(~7,200 rpm).

Because of these differences,

todays hard drives are able to store

large amount of information in a verysmall sp ace. According t o J.P. Free-

man Co. of Newtown, Conn., more

and more companies are turning to

disk-based media for backup and re-

covery. In those settings, tape is usedprimarily as an archiving technology,

and the amount of data that needs to

be archived is growing rapidly.

Disk-based solutions are typically bet-

ter suited to backup and, particularly, re-

covery operations, whereas tape is ex-

tremely cost-effective for archiving.

Moreover, an intermediate disk layer can

provide a steadier stream of data to the

tape drive, thus improving performance.

Hard Drive Operation ExplainedAll disk drives operate on magnetic

principles and are based on the basic

physics principle that states as elec-

tric current flows through a conduc-

tor, a magnetic field is generated

around that conductor. This magnetic

field then influences the magnetic

material in the field.

A hard disk uses round, flat disks

called platters, coated on both sides

with a special media material designed

to store information in the form of mag-netic patterns. The platters are mounted

and stacked onto a spindle. The platters

rotate at a high speed (3,200 to 7,200

rpm), driven by a special spindle motor.

Special electromagnetic read/write

devices called heads are mounted

onto sliders and used to either record

information onto the disk or read in-

formation from it. The sliders are

mounted onto arms, all of which are

mechanically connected into a single

assembly and positioned over the sur-face of the disk by the actuator. A logic

board controls the activity of the other

components and communicates with

the rest of the digital recorder.

IDE Cheaper, But SCSI Better

Integrated drive electronics (IDE)

are the most common types of incor-

porated drives used by DVR manufac-

turers. These types of drives put most

of the electronics on the drive itself.

The encoding and decoding and thecontrol signals are done on the circuit

board under the drive. The adapter

card just relays the signals from the

drive to the digital recorder.

However, with the need for faster

processing speeds than IDE drives

can deliver, some manufacturers, es-

pecially in high-end DVR systems,

have switched to what is known as a

small computer systems interface

(SCSI) drive assembly.

SCSI is a much more advanced inter-face than IDE and has several advan-

tages. SCSI drives are independent; their

bus is completely separate from the

usual PCI or ISA found in IDE designed

digital recorders. They also do not rely

on the basic input output system (BIOS)

to communicate with the system, in-

stead using a special adapter card.


Hard Drive Assembly

Disk-based solutions are typically bet-ter suited to backup and, particularly,

recovery operations, whereas tape isextremely cost-effective for archiving.

Disk 1 Disk 1

Write Mirror

Compressed Video Output

Disk Mirroring Illustrated

Disk mirroring is a tech-

nique in which data iswritten to two duplicate

disks simultaneously.With this method, if onedisk fails the system can

automatically switchover to the other drivewithout causing any loss

of recorded or retrievedvideo information.

Controller

Platters

Actuatorw/Read/WriteHeads


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You can connect as many as seven

SCSI devices to the adapter, without

the computers knowledge. The

adapter keeps track of the data flowacross the SCSI bus. Each device gets

its own SCSI address. Each device can

talk with the other SCSI devices across

the bus, all independent from the

computer, which, in a nutshell, means

SCSI drives increase the operating

speed and performance of a comput-

ing device.

Which one is the right for you?

IDE drives are less costly, and have

a slower transfer rate and less flexibil-

ity (unable to expand above fourdrives in a system) than SCSI drives.

SCSI drives, on the other hand, offer

faster transfer speeds and greater sys-

tem flexibility. However, all this comes

with an increase in equipment costs.

The bottom line is if you want it cheap

and simple with good performance, use

IDE drives. If you want maximum per-

formance and flexibility and have the

money to pay for it, then use SCSI.

RAIDs Prevent Data LossAnyone who has worked with com-

puters (and we all know DVRs are ba-

sically computing systems) is well

aware that hard drives can fail. With

this failure comes a loss of all stored

information among a sea of electron-

ics, magnetic fields and metal parts.

With that in mind, how can stored

information be protected? The an-

swer is what is known as the redun-

dant array of independent (once called

inexpensive) disks (RAID).

There are five commonly used

RAID configurations each provid-

ing disk fault-tolerance and offering

different trade-offs in features and

performance. In addition to these five

redundant array architectures, it has

become popular to refer to a nonre-

dundant array of disk drives as RAID-

0. However, since it is not redundant,

it does not truly fit the RAID acronym.

RAIDs incorporate mirroring tech-

niques of data, data striping, or a

combination of both. The level orRAID configuration usually depends

on the application and degree of fault

required for that application.

Mirroring is a technique in which

data is written to two duplicate diskssimultaneously. With this method, if

one disk fails the system can automat-

ically switch over to the other drive

without causing any loss of recorded

or retrieved video information.

Stripingis a method of combiningmultiple drives into a single logical

storage unit. Striping involves parti-

+ + +

Com-

eo

pres-

Info-

sed

rma-

Vid-

tion

Disk 1 Disk 2 Disk 3 Disk 4

Compressed video information

Comparison of RAID-0, -2 and -3 Configurations

Disk 1 Disk 2 ECC ECC


Disk 1 Disk 2 Disk 3 Parity


RAID-0:Striped disk array

RAID-2:Hammering code

RAID-3:Striped with parity drive

Here we see three of the five common random array of independent disk (RAID) levels. In

RAID-0 (top), data is broken down into blocks and each block is written to a separatedisk drive, resulting in higher data throughput. In RAID-2 (middle), each piece of datahas a hamming error correction code (ECC) word recorded on the ECC disks. When read-

ing, the ECC verifies correct data or corrects single disk errors. In RAID-3 (bottom) the

data block is subdivided (striped) and written on the data disks. Stripe parity is gen-erated during writing, recorded on the parity disk and checked on reads.


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tioning each drives storage area into

stripes, which are then interleaved so

the combined video storage consists of

alternate stripes from each disk in thearray. The more drives in the array, the

more the average access time for the

array approaches the worst-case sin-

gle-drive access time. Synchronized

spindles assure every drive in the array

reaches its data at the same time.

As mentioned, RAID-0 is not redun-

dant, hence does not truly fit the RAID

acronym. In Level 0, data is broken

down into blocks and each block is

written to a separate disk drive, result-

ing in higher data throughput. Since noredundant information is stored, per-

formance is very good but the failure of

any disk in the array results in data loss.

RAID-1 provides redundancy by

writing all data to two or more drives.

The performance of a Level-1 array

tends to be faster on reads and slower

on writes compared to a single drive,

but if either drive fails, no data is lost.

The main disadvantage is that the cost

per megabyte of storage is higher

since one drive is used to store a du-plicate of the data. This level is com-

monly referred to as mirroring.

In RAID-2, each bit of data is written

to a data disk drive. Each piece of data

has a hamming error correction code

(ECC)word recorded on the ECC disks.

When reading, the ECC verifies correct

data or corrects single disk errors.

This form of RAID is intended for

use with drives that do not have built-

in error detection. All SCSI drives sup-

port built-in error detection, so this

level is of little use when using them.

In RAID-3, the data block is subdi-

vided (striped) and written on the

data disks. Stripe parity is generated

during writing, recorded on the parity

disk and checked on reads. Byte-level

striping requires hardware support

for efficient use.

RAID-4 stripes data at a block level

across several drives, with parity stored

on one drive. The parity information

allows recovery from the failure of any

single drive. The performance of aLevel-4 array is very good for reads (the

same as Level 0). Writes, however, re-

quire parity data be updated each

time. This slows small random writes,

in particular, though large writes or se-

quential writes are fairly fast.

Because only one drive in the array

stores redundant data, the cost per

megabyte of a Level-4 array can be

fairly low.

RAID-5, which stripes both data

and parity information across three or

more drives, is the most popular RAID

level. It is similar to RAID-4 except that

it exchanges the dedicated parity drive

for a distributed parity algorithm,

writing data and parity blocks across

all the drives in the array.

Fault tolerance is maintained by

ensuring that the parity information

for any given block of data is placed

on a drive separate from those used tostore the data itself.

Managing Networked Storage

So far, the methods covered for stor-

ing video information have involved

the storage unit as an integral part of

the recording device. The only external

equipment required (in some cases) is

an additional storage backup device.

However, the growth of IP-based

cameras and recording equipment has

increased the need to provide initial

storage, storage backup and storage

management for vast amounts of video

information is now becoming an issue.

The methods by which the infor-

mation is stored remain the same

(DAT, HDD, RAID, SCSI, etc.); howev-

er, the way the information is man-

aged is changing.

Network attached storage (NAS) is a

data configuration or medium using

storage devices that connect directlyto a network. These devices are IP


Storage Storage Storage Storage

Storage

LAN

NAS

Device

Network Attached Storage vs. Storage Area Network

Fibre ChannelSAN

Storage Storage Storage Storage

Storage

LAN

NAS

Device

NAS

SAN

Network attached storage (NAS) is a data configuration or medium using storage devicesthat connect directly to a network. These devices are IP-addressable and be accessed byoperators via a server that acts as a gateway to the video information. A storage area net-work (SAN) represents a way to separate the server and storage into two independently

managed systems, thereby simplifying the complexity of the overall IT infrastructure.


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addressable and be accessed by oper-

ators via a server that acts as a gate-

way to the video information.

The advantage of NAS is the storagecan be centralized, easily expanded

and managed. Additional NAS boxes

can be plugged into the network to

handle an increased number of sys-

tem operators as well as the need for

increased storage.

NAS deals with storage at the file

level, and is utilized for general pur-

pose file sharing. However, it does not

address the problem of backup.

Astorage area network (SAN) repre-

sents a way to separate the server andstorage into two independently man-

aged systems, thereby simplifying the

complexity of the overall IT infrastruc-

ture. SANs use special switches as a

mechanism to connect the devices.

These switches make it possible for de-

vices to communicate with each other

on a separate network, which offers

less crowding of a standard network.

According to Framingham, Mass.-

headquartered research company In-

ternational Data Corp. (IDC), SANswill account for 70 percent of all net-

work storage by the end of this year.

NAS provides a quick and easy way

to add general-purpose, shareable

storage space to users and groups,

while SAN separates the ser ver and

storage into two systems, making the

overall network infrastructure simpler.

With all of this digitally stored in-

formation, more and more people are

wonder ing how it can be protec ted

from being altered in any way (seesidebar below). Anyone who has used

digital cameras and image software

can appreciate this potential vulnera-

bility. It does not require much train-

ing for anyone to have the capability

to alter an image.

Every photo software program offers

features from removing red-eye to plac-

ing your photo anywhere in the world.

This is a great tool for the photographic

society; however, it can cause a great

many problems in the security field.History has shown that recorded

video information on standard VHS tape

has been accepted by the court system

as evidence. The alignment of the mag-

netic particle on the tape as well as the

video signal equalization pulses embed-

ded in the tape make it impossible to

alter the tape without being noticed.

The next installment of the Digital

Video for D.U.M.I.E.S. series will dis-

cuss the parts and pieces of DVRs and

their ever-increasing features. Lookfor it in the SSIs special September

2004 ASIS Show Issue.

Robert (Bob) Wimmer is president of Video SecurityConsultants and has more than 33 years of experi-ence in CCTV. He has been a training consultant forseveral of the industrys leading CCTV manufactur-ers and other organizations.He has also written nu-merous articles on CCTV applications and advanc-ing equipment technology.

To date, there have been no challenges of the digital videoevidence that has been submitted and accepted in

U.S. courts. However, this does not mean DVR manufac-

turers have forgotten or eliminated image authentication for

their equipment.

In order to satisfy the Daubert Criteria a legal ruling that

states a judge must decide whether scientific evidence is relevant

and reliable digital video authentication technology must

demonstrate it conforms to recognized standards, and that error

rates have been deemed acceptable by the scientific community.

Since there are currently no standards for digital video authenti-

cation, FIPS-140-2 (Federal Information Processing Standard) certi-

fication for the signature software has been (in some circles) iden-

tified as a foundation for building the necessary acceptance.

Efforts have also been made to define high-level guidelines by

organizations such as the Law Enforcement and Emergency Ser-

vices Video Association (LEVA), Scientific Working Group on Digi-

tal Evidence (SWGDE) and Scientific Working Group on Imaging

Technology (SWGIT).

Many of the manufacturers are incorporating these recommen-

dations as well as suggestions from countries that have been sub-

jected to court approvals.

The main comment is that the image for evidence shall be

original.That means special post-enhancement image programs

could not be incorporated when using a video clip as evidence

in a court of law.The other statements made included terms

such as write once, read many (WORM), check sum and digitalwatermarking:

WORM a form of optical disk authentication technology

that allows data to be written onto a disk just once. After that, the

data is permanent and can only be read.There is no standard for

WORM disks,which means they can only be read by the same type

of drive that wrote them.This may hamper their acceptance in the

DVR industry.WORM is also called CD-R.

Check sum a method that analyzes the building blocks of a

video image its pixels or picture elements.Once digitized,each pixel

will be represented by a numeric value. After each row of pixels a

count is made of the total value and this number is encoded and stored.

Upon authentication, the numeric value is compared and if the

values are different, it indicates that the image is no longer original.

Some use a total of all pixel values, while some store each row of

the recorded image.

Digital watermarking a method in which information

such as date/time or other verifications are inserted into a digital

image file that identifies the files authenticity.The name comes

from the faintly visible watermarks imprinted on stationery that

identify the manufacturer of the stationery.

The actual bits representing the watermark must be scattered

throughout the file in such a way that they cannot be identified and

manipulated.The digital watermark must be robust enough so that

it can withstand normal changes to the file, such as reductions

from lossy compression algorithms.

Authenticating Digital Video Images


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For more information on these and other Honeywell Video Systems

products, please call our Sales Support Center at 1.800.796.CCTV. www.honeywellvideo.com

Fusion SampleRecording Chart

8 to 32 camera units

Capture rates up to 480 ips

Live viewing up to 480 ips

Multiplexed analog output

Remote accessibility/notification

Text insertion interface

Display maps of facilities

Smart Search

Index Search

Easy installation and operation

Fusion is more than a standard DVR Series. It is an

intelligent, world-class digital management system

combining multiplexing, motion detection, audio, text

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extremely versatile, upgradeable unit.

With its advanced compression algorithms, fast

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next generation of DVR technology.

Fusion RemoteView Software

Fusion DVR

Reader Service Card No. 103

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Digital Video Part 2