While digital video surveillance systems offer an embarrassment of riches compared to their analogue ancestors, they still require thoughtful design and deployment to ensure maximum cost-effectiveness. Among the various criteria that impact surveillance digital video recorder (SDVR) system value, storage capacity can be particularly significant and easily misunderstood.
- Higher image resolution
- More active cameras
- Longer archival periods
- Intelligent video recognition
Abundant storage capacity is a fundamental enabler of such capabilities, and it is here that some video surveillance deployments can go amiss. In an effort to minimise costs, some SDVR systems may utilise multiple low-cost, low-capacity hard disk drives (HDDs) to meet their storage requirements. On its surface, this approach appears to be a viable option to reduce storage expenses.
In conventional computing environments, hard drive capacity is typically viewed only in quantitative terms; how much data can the storage system hold? But in the context of SDVR solutions, drive capacity plays a key role in determining both the quantity and quality of data that the system can store.
Because 24×7 video streams are the very lifeblood of SDVR systems, to deliver superior performance and efficiency in a given security environment, these systems must have sufficient storage capacity to address three fundamental video parameters:
Quantity—the number and time duration of the video streams
Quality - the image quality of the video streams, expressed in terms of frame resolution (for example, 1280×1024 pixels) and frames per second (fps)
Archiving—the length of time the video streams will be stored
Video Balancing Act
Once the specific balance of video data quantity, quality and archiving required for a given security application is determined, its easy to estimate the amount of storage capacity an SDVR system must include. Simply go to one of the video surveillance storage matrix tables to select the table row that lists the frame resolution and fps needed for each 24×7 video stream, then read across to find the nearest desired archival period (shown in days) and the corresponding drive capacity required for each individual stream.
Note: Table 1 reflects MPEG-4 compression, while Table 2 reflects the H.264 encoding; results will vary depending on video compression formats and specific video recording applications used.
The tables show the enormous variation in the hard drives recording capacity based on a 24×7 video streams resolution and frames per second.
With so many security applications entailing dozens of cameras and 24×7 video streams, it soon becomes apparent that a typical SDVR systems storage requirements can easily reach hundreds of gigabytes. In the following three examples, the varying video profiles of different security environments (and the storage capacities they require) are compared.
Example A: Extended Archiving
There are many businesses (point-of-sale and retail, restaurants, banks, and so forth) where high-resolution, full-motion 24×7 video streams are simply overkill. Typically employing a modest number of fixed cameras to record customer activity, SDVR solutions in these environments are able to employ lower image resolution and fewer frames per second while still delivering sufficient video detail for subsequent review as needed.
When the quality of an SDVR systems 24×7 video streams can be relatively low, the benefits of greater HDD capacity come from enabling longer archival storage. Archive periods can be economically extended from a select number of days to months, or even years; indeed, continuous video signal at 10fps/352×240 resolution can be streamed onto a 4TB drive for 1064 days with MPEG-4 compression and an astounding 1656 days with H.264 encoding (refer to Table 1 and Table 2).
Example B: Enhanced Quality
Environments with more stringent security requirements (for example, schools, public buildings and airports) rely on 24×7 video streams with higher resolution and more frames per second to better identify suspicious persons and activity. Coupled with broader camera deployment, the enhanced video quality of such streams gives security personnel a more detailed, comprehensive view of the areas under surveillance.
Not surprisingly, the higher resolution and frame rates of such 24×7 video streams can significantly increase the capacity requirements of the SDVR system. As shown in Table 1, just one continuous video stream at 20fps/704×480 image resolution can fill a 1TB drive in only 42 days with MPEG-4 compression. Table 2 shows how H.264 encoding extends video storage in this scenario to 66 days. Multiply that by the dozens of 24×7 video streams that such SDVR systems typically employ, and the need for massive storage capacity quickly becomes clear.
Example C: Intelligent Video
Designed for maximum-security surveillance environments, intelligent video takes full advantage of the exceptional detail found in high-resolution, full-motion (30fps) 24×7 video streams to recognise visual patterns. The best-known use of this technology is facial recognition; intelligent software analyses the faces of persons in stored surveillance footage, comparing their features to those of known suspects/criminals on file. When a match is found, the application automatically notifies security personnel for follow-up investigation.
These high-resolution, full-motion 24×7 video streams deliver superlative visual quality, but do so at a price; they consume vast quantities of storage capacity. The tables show the voracious nature of such streams. Using MPEG-4 compression, a single continuous stream at 30fps/1280×1024 resolution fully exhausts the capacity of a 4TB drive in just 32 days, while H.264 encoding delivers approximately 56 days of the same quality video.
Boasting an unprecedented blend of visual detail and storage capacity, digital video recorder systems are spearheading a new era of surveillance effectiveness and flexibility. Purpose built surveillance drives are key enablers of this revolution, storing enormous quantities of video data at remarkably low cost per GB. The result is surveillance systems that can seamlessly accommodate the unique image quality and extended archival needs of modern security environments.