Compression Methods for Video Security

In the world of Video Security the biggest headaches for designers and administrators of the system is the ability to manage the data storage. Data storage is dependant on how big of a storage device you built into the recorder, Digital Video Recorder (DVR) or Network Video Recorder (NVR). There are many different ways to utilize the space you have available through the configuration which we will discuss in the next topic, but this topic is mainly going to concentrate on the how the compression of the video is done to not take up all the resources of the storage that is available.

Compression is basically to take the video and compress or “shrink” it down from its raw form to media such as a Hard Disk Drive (HDD). There are several different forms of compression used in the security industry and those are MJPEG, MPEG4, and H.264. These compression forms allow administrators to keep video for a given period of time without comprising its video integrity. As mentioned earlier there are other avenues for manipulating the configuration to give you more bang for your buck from the HDD, but this is the biggest player.

MJPEG stand for Motion Joint Picture Experts Group, which was originally developed for multimedia PC applications, has also been incorporated into the video security environment. It is an interlaced form which uses every frame as a picture and requires a lot more HDD storage as each image or frame captured can be very large. An example would be for a given period of 5 minutes of video the storage required for that 5 minute period could be anywhere from 150-200MB of video. Now, this is a very large chunk to take from the hard drive available for such a short period of time, but can provide explicit information if need to provide to the authorities. MJPEG is the only form of evidence admissible in the court of law in its raw form. The drawback to providing irrefutable evidence is the ability to have funding for such an enormous storage requirement if lets say you needed 30 days of recording. This is where our next compression method comes in MPEG-4.

MPEG-4 stands for Motion Picture Experts Group and was intended to serve the Audio Video World including broadcast television. We have all come across MPEG4 video whether it be watching TV, on YouTube, or recording home movies. This technology also is prevalent in the security arena by which it compresses the video to through audio and video coding. The concept behind MPEG4 is that not all the video or frames is actually recorded. It consists of I frames and P frames which have gaps in between to have a software program fill in the pieces of the previous and next frames with the apparent video on each of those before and after frames. This is an excellent way to conserve HDD space, but is not admissible in the courts in its raw form. The reason why it is not admissible in the courts is because if the missing gaps. When information is missing and was filled in by software there could have been manipulation of that video. The way to over come this is by having authenticating key sequences or watermarking the video through proprietary means by the manufacturer of the recorder which it was recorded on. This way there is a check and balance on the authentication of that video and would be played on specific player software to prove its authenticity.

The final compression method is H.264 which is just another name for MPEG4- Part 10 and takes the compression of video surveillance storing to another level. This method is still being reviewed, but has been released and many have started to adopt it into their recorders. The method is the same using the frames and filling the information, but the complex algorithms it uses makes storing the video for longer period of time on the same HDD size. The admissibility remains the same in the court of law and would need to follow the same standards as MPEG4 where as you would have to have a player to play the video. This will prove that it is authenticate video.

From a designing and storage perspective compression plays a huge role in the video surveillance field. It could mean the difference in having 2 days of video compared to 30 days. I am sure that there will be other methods to come in the near future and as they do I will be sure to keep you in the loop.

My next topic will be on How to configure a DVR!

See you soon.

Kal