provided by: 
REPLACING EXISTING CAMERAS DECISION
Q: Can we use existing surveillance cameras in a digital system?
A: Surveillance cameras used in a digital system must be of a reasonably high quality. A poor camera that does not have a strong S/N (Signal to Noise) ratio will result in poor video and will require a much larger amount of disk space to store video. The noise in the video signal is often not recognized as noise. Thus the system works very hard to record all of the noise. This results in the system's hard disk filling up with very large files.
EVALUATING COMPRESSION
Q: What are the different kinds of video compression? Why should one format be used over another?
A: Effective video compression is the key enabling factor in the emergence of digital video surveillance as a replacement for traditional CCTV systems based on analog VCRs. When evaluating different types of compression it is important to consider not only the effectiveness of the compression, but also on what system the video is going to be played.
If the compression format is a well known type, it is both likely to be supported by mainstream viewers (such as Microsoft's Windows Media Player) and can be archived for use in the distant future. Proprietary compression algorithms often offer superior performance but come at a price of compatibility. Many proprietary solutions offer a conversion tool. However, this tool often takes a significant amount of time to run.
The most common video compression formats used in video surveillance are: M-JPEG and MPEG-4. Over time these will be supplanted by new standards: AVC (Advanced Video Coding), MPEG 4 part 10 and H.264. These compression rates will enable new video applications in products ranging from cell phones, PDAs or video-iPods for security, all the way to high definition television broadcast.
Finally, there are many DVRs that take an alternative approach to storing and compressing video. These DVRs store a series of JPEG images individually and replay them on demand. An advantage of this approach is that it is possible to play back the video in almost any web browser. It is more than likely that some clever JavaScript routines are used to present the JPEG images in sequence to the user. The specific advantage is that there is no need to download a browser plugin or any other code into your customers' computers to view the video. The disadvantage is that usually the frame rate is quite low (i.e. greater than 1 second).
RESOLVE TO RESOLUTION SIGNIFICANCE
Q: How important is resolution?
A: In a word, VERY. The better the resolution, the more likely an object or person will be identified after an event occurs. Unfortunately, the higher the resolution, the more disk space and bandwidth is needed to support the increased amount of data. Many security cameras support higher resolutions and when combined with a DVR or NVR these systems can offer impressive results.
TODD RADERMACHER is co-founder of Presidio Technology, San Francisco, CA. Presidio provides a managed Internet based video surveillance service.
author: By Todd Radermacher