Today many security managers and business professionals are switching to digital options for their CCTV. While this represents a slightly larger investment, it also largely increases flexibility, quality and efficiency through a variety of different options and functions. One of these options is the ability to select which format to compress videos in.
On your computer you may have downloaded a variety of videos; if you look at each of these by right clicking on them and selecting ‘properties’, you will notice that some of them are different file types. These will vary from .WMV to .MPEG to .AVI and each has different properties. What this refers to is the videos’ ‘compression type’. If you consider the size (in terms of kilobites or megabites) that an image size takes up, you can imagine why it’s important that these images are somehow ‘cut down’ in order to save space when potentially millions of them are strung together to create a video. This happens at the level of the code (the language that the computer or video device reads), but can be visible in the videos’ appearances as washed out colours, lower resolutions, blurry edges or fuzzy motion. The aim here is to find a satisfactory balance between viewing quality and file size – so that you can store as much information onto a hard drive or disk as possible without sacrificing too much detail.
When recording with a DVR (digital video recorder), this works in much the same way and the videos must be compressed when they’re saved. Only in cases of CCTV, compression type is far more crucial as you’re not only dealing with larger quantities of footage (sometimes hours’ and hours’ worth) but also with delicate situations that require the highest possible frame-rates and resolutions if you are to correctly identify problems. For these reasons, when purchasing a DVR it’s highly important that you find out what compression types it supports (sometimes referred to simply as ‘video formats’) and what the different titles represent.
The two main types of compression format for digital CCTV are ‘H.264 format’ and ‘MPEG’ (AKA Motion JPEG, and by which is usually meant MPEG2). The key thing to note here however, is that H.264 format is also known as MPEG4, meaning that it is in fact an updated version of the alternate format. H.264 video compression format therefore drastically reduces both the bandwidth and storage requirements of the files by keeping them small while keeping the image quality high. Usually however this results in a lower ‘bit rate’ for the video which means that fewer ‘bits’ of information are available per second, but the method of encoding ensures that these lost ‘bits’ are unnecessary (high frequencies for example). With an average set up with four cameras at thirty frames per second and a resolution of 320 x 240 (with motion sensors), you can expect MPEG4 compression to provide 80 hours worth of footage at 20-25 gigabites.
However unlike MP2, MP4 has no government enforced standard and as such does not have universal interchange across codecs of various designs. This means that MP2 is more flexible and adaptable as well as having a higher bit rate giving it its own unique advantages. Fortunately however, today most cameras support both formats and even where they do not file conversion is often available.
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