IP Video Design Considerations
Different requirements factor into bandwidth calculation
- By Mike Mathes
- Aug 01, 2011
When considering IP video design, a great
deal of attention is usually given to bandwidth,
processor throughput and storage.
Rightfully so, but many other implications of an IP
video system are often overlooked.
When calculating bandwidth, processor throughput
and storage, each camera, encoding algorithm
and VMS has different requirements. It’s critical to the
overall system that each of these issues is considered.
But what makes an IP video system different from an
analog system other than these obvious issues?
A primary difference versus traditional analog systems
is the variety and flexibility of image resolutions
and frame rates and how these options impact the
overall system design.
Designers often use only resolution and frame
rates to determine the bandwidth and storage requirements
of the system. The implications go much deeper
to the heart of the overall system design. Analog
cameras provide less than 0.5 megapixels of image
resolution. Today’s cameras provide 1, 2, 3 and 5
megapixels as a matter of course, with even higher
In an effort to shortcut the design process,
we often see resolutions and frame rates that are
much higher than necessary. This leads to increased
system cost for servers and storage.
But it’s not just the first cost of the server. A
server consuming 300 watts will cost more than
$1,000 per year in energy just to run and cool it.
Could the system be designed with fewer servers?
With today’s green initiatives taking center stage, it
behooves us to ask these questions and undertake an
So, what are the fundamentals of proper system design?
It starts with understanding the application for
any given scene. Based on the application, first determine
the level of resolution needed. There are three
general principles or levels: detect, classify and identify.
Detection. The system will capture general information.
You’ll be able to see crowds, traffic flow or
an individual object moving in the scene. General
surveillance and detection requires a minimum of 6
pixels per foot.
Classification. If you need to be able to classify an
object within a scene, the minimum pixel count is 20
per foot. At this resolution, you’ll be able to classify
objects as people, animals and vehicles.
Identification. The highest level of resolution.
Forty pixels per foot is considered the minimum to be
able to identify an individual or read a license plate.
Proper analog system design also should incorporate
these principles. Internet Protocol, with its various
resolutions, can provide greater flexibility, helping
to reduce camera count and the associated infrastructure
Once the resolution level is determined, you’ll
need to calculate the total resolution required for a
Measure the width of the subject field at the required
distance. Multiply the width by the pixels per
foot required and you’ll have the number of pixels required
to capture the scene. You can then determine
what resolution the camera or cameras can provide to
achieve the necessary coverage.
Another often-overlooked fundamental of the
design is lens selection. Proper lens selection is critical,
particularly when dealing with high-definition
IP cameras. Lower-quality lenses will not focus to
the resolution of a high-definition sensor. This reduces
the effective pixel count, wasting money that’s
been spent with the intent of achieving a higher
While it’s not the intent here to provide a tutorial
on lens selection, it’s important to understand sensor
size and format, and how that relates to an appropriate
lens for a specific field of view and resolution.
With wider views come the need for greater depth
of field, particularly in scenes where the view isn’t
straight on. A road or path angling away from the
camera presents the subjects at increasing distance
as they move across the field. While this occurs with
analog systems, a 5-megapixel camera can experience
the effect fourfold and requires a more calculated approach
when selecting a lens.
A higher pixel count isn’t always better. By following
the above design principles, the pixel count can be
optimized and lower-cost, lower-pixel count cameras
can be used, keeping the bandwidth and storage requirements
to a minimum. Remember that doubling
the pixel count can double bandwidth and storage but
will only increase resolution by 50 percent.
Another fundamental principle of IP design is
frame rate. The tendency of designers and users is toward
higher frame rates. Many cameras offer a host of
frame rate adjustments right up to full-motion 30 fps.
Because encoding algorithms MPEG and H.264 rely
on scene differences, an increase in frame rate doesn’t
proportionally increase bandwidth or storage. As the
frame rate increases, the difference from one scene to
the next reduces, and therefore less data is in the stream.
There is a price to pay, however. Viewing workstations
still need to fully recreate each frame. Higher frame
rates and encoding such as H.264 put more demands
on the processors in these workstations.
To help determine a desired frame rate, we can
apply some logic. How fast is the subject moving
through the scene? How wide is the scene? How
many images of the subject moving through a scene
do you need? One image of a person may not be
enough for identification, but it could be for a license
plate. Once you know these criteria, you can determine
a minimum frame rate without overtaxing the system.
A final word on cost: many cost comparisons look
at equivalent camera counts. By now you should realize
that’s not an effective comparison. Costs for an IP
system should be compared to an analog system of
equivalent coverage. Often, with fewer cameras and
reduced infrastructure, both the initial costs and ongoing
operation of an IP system will be less than an
Today’s advanced IP technologies require an indepth
understanding of system design. This goes
much deeper than understanding the bits and bytes
of bandwidth, processor throughput and storage.
It is necessary to understand how to apply various
camera resolutions and frame rates to design a quality
Ensure your system designer and integrator have a
solid understanding of these design principles before
finalizing your next project.
This article originally appeared in the August 2011 issue of Security Today.