A User's Guide to Digital Video Surveillance

Compression Technology Challenges


One of the problems of the older MPEG formats is their inability to properly record fast moving objects. When objects are moving quickly DVR's with older “simple” Codecs have a tendency to record blurred or distorted images, including mosaic patterns as you may observe sometimes on digital television broadcasts using similar technology.

compare Mpeg4 vs H.264

While a scene or image is being processed, the next scene follows in sequence. As a result, there is latency, even if in milliseconds, due to time required to compress and decompress the images. Accordingly, when it can’t keep up there are voids.

In order to efficiently negotiate a transition from one frame to the next; the codec needs a way to identify and predict what is happening in the coming scene. “Simple” codecs do not have the best of abilities to compensate or predict; resulting in potentially blurred or blocky images. So beware. When evaluating a DVR solution for video quality, it’s not the images with minimal motion that are of as much concern as the ones containing rapid motion. In older compression technologies, to minimize the “blockiness”, the bitrate is boosted to a high level. This introduces the other concerns previously discussed of necessary resources to drive the escalated bitrate.

Can it still record 30 frames per second, without dropping frames and can it perform across multiple channels simultaneously? Is it going to overheat? Is it going to crash? 

Also, by boosting the bitrate, which means larger file sizes, the storage requirements become massive. In the end, there is no fix for fast moving images using older codecs, the best that can be hoped for is a reduced amount of mosaic images with large storage requirements.

Part of the problem is older compression technologies were never designed for security or the new digital era. The first concern was simply how to compress video from a tape to a CD or DVD. So the variables and environment were somewhat controlled.

 

 
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