Bandwidth versus video quality; it’s the oldest battle in IP video system design. Calculating a system’s bandwidth load is a vital task, but it doesn’t have to be a daunting one. Answering the right questions is critical.
Question 1: What’s the video system use classification?
Three primary classifications of IP video surveillance systems that directly affect bandwidth are observation, recognition and forensic review. What is the end-user hoping to accomplish with each camera in the system?
If the customer is installing/using an IP system for the first time, it’s the integrator’s responsibility to present a realistic depiction for 1.) what classification is required from each camera and 2.) what is possible with today’s technology within their budget.
Question 2: What are the basic video quality needs?
Once use classification is chosen for each camera, this will determine how you configure the three basic settings that balance bandwidth and user expectations:
- Frame rate
When the user must review video data forensically, they will most likely benefit from the greatest amount of resolution. Observation, on the other hand, requires a lower resolution but with a higher frame (re-fresh) rate.
The more resolution and frame rate required for each camera, the more video data that traverses the network. This is where compression comes into play.
Video compression reduces and removes redundant video data so that a digital video file can be efficiently sent over a network. Video quality, however, can be affected depending on the compression technique and percentage—which is why you want to use the most efficient techniques available. H.264, for example, can reduce the size of a digital video file by more than 80 percent without compromising image quality compared to Motion JPEG and as much as 50 percent more than MPEG-4.
Determining adequate compression levels will rely on a test-and-see exercise to ensure the customer is happy with the video quality versus the corresponding bandwidth levels.
Remember, if the end-user has a minimum spec for frame rate and resolution, the only adjustment you can make is compression. If it approaches the point where image quality is less than desirable, you’ll need to consider upgrading the network hardware.
Question 3: What’s the scene complexity?
Scene complexity is comprised of the activity and visual environment in the camera’s field of view and it affects overall bandwidth on a camera-by-camera basis.
A camera aimed at a white wall will have far less image complexity than one overlooking a tree line on a fall New England day. This is why camera vendors try to select colorless and boring rugs for their tradeshow booths—since a patterned, colorful rug could spike bandwidth levels and make for a poor demo.
Next, work with the end-user to estimate how much activity they anticipate in each camera’s field of view. A camera at the front door will have much more activity than one overlooking the loading dock.
Most manufacturers offer interactive system design tools to calculate bandwidth for each camera based on the video quality levels selected (frame rate, compression, resolution, etc.) compared against different scene scenarios (intersection vs. schoolyard vs. lobby, etc.).
Question 4: Which cameras multi-stream?
The first three questions cover how the settings and performance parameters affect bandwidth levels for a camera’s stream. However, today’s IP cameras employ multi-stream capabilities. How many streams do you plan to use and where is each one going?
A basic use of multi-stream is to have one stream sent for live viewing while a second stream of the same scene is sent for storage. These streams are configured differently on a per-needs basis (i.e. the live view is typically lower resolution, while the storage stream is HDTV-quality for forensic video). This creates two separate streams on the network coming from one camera and must be taken into account for calculations.