digital video part 2
TRANSCRIPT
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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
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Part 2of 4
By Bob Wimmer
Video Security Consultants
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.
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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
Compressed video information
Disk 1 Disk 2 Disk 3 Parity
Compressed video information
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
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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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With its advanced compression algorithms, fast
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Fusion RemoteView Software
Fusion DVR
Reader Service Card No. 103