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Translating the Language of Compression

  
  
  
  

By Kevin Klemmer, Pivot3

Video CompressionThe IP surveillance market grew immensely over the past decade with many new players emerging and traditional CCTV manufacturers expanding into networked technologies. With the avalanche of new companies and technologies cascading over the industry, there is no wonder there is confusion surrounding the proper configuration of networked-based security technologies, and what is necessary for a successful and reliable deployment.

Resolution, compression, frame rate, retention time and motion in the field-of-view are some of the main factors to consider. While most of these factors are pretty straightforward, compression is the most confusing and daunting to address. What is MJPEG, MPEG4, H.264 or J2K? Lossy or lossless?

Video compression is complex but described simply, it removes redundant data from the field-of-view to make video file sizes as small as possible so users can store more data. There are two primary types of compression: Lossless and lossy compression.

How can you choose which compression is best for a particular application? It ultimately comes down to cost. The first factor is insurance, which refers to whether data can be used for evidentiary purposes. If a user requires the original video data for legal reasons then lossless compression is what is needed. If not, lossy compression is an ideal fit.

Lossless data compression is an algorithm that enables the exact original data to be reconstructed from the compressed data. An example of lossless compression is JPEG2000, although there are some versions of JPEG2000 that are lossy compression standards as well.

Lossy data compression actually discards some of the data during encoding to deliver a much smaller file size. This is very useful from a storage perspective, but can be an issue when recreating the video stream. Most of the commonly used compression algorithms are lossy and do a fine job of recreating the data for general purpose surveillance needs. Examples include MPEG4 and H.264.

The second cost factor is the storage and servers required. There is a substantial trade off in terms of storage costs associated with different compression types. Lossless compression requires more storage than lossy compression. A VGA (640 x 480 pixels) video stream for a single camera at 10 frames per second for a single day of retention, uncompressed, requires more than 700GB of storage. The same configuration with MJPEG requires approximately 75GB; MPEG4 equates to 10GB; and H.264 needs 4GB.

The cost per gigabyte has decreased significantly over time and can be less than $1 per GB for the average end user. This is due to innovations in software-based RAID protection and use of commodity hardware to accomplish what previously required proprietary hardware and fixed RAID controllers. The flexibility offered to end users with next generation storage servers is significant, and is helping to provide exceptional data and software protection at a fraction of the price.



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