Digital video encoding in surveillance systems
The encoding or, more simply, the compression of the digital video signal is of great importance in video surveillance. To understand why, let’s go back to recent history.
The digital method of video recording was used for the first time in the 80s of the last century. Then it was a clean, uncompressed video that required a lot of memory to store and use. It is clear that at that time there were no devices to record such volumes of information, and then the first codecs were invented, specifically designed to compress the form.
Since then, compression and encoding have been used when recording any video information. Otherwise downloading, processing, editing, playing and storing video files will take a great deal of time and huge stores of data. Coding eliminates all of these problems.
The encoding process itself is quite simple. When special codecs are used, the video data stream is continuously analyzed by them and unnecessary / unimportant chunks of data are simply cut off, helping to significantly reduce video file size.
Today, there are two types of video compression: frame-by-frame (intra-frame) and inter-frame encoding.
Frame-by-frame compression treats each frame of the video as a separate still image, like a photograph. This technology allows good quality videos to be obtained, but at the same time the file size is slightly reduced so that with this encoding all the frames are saved, even if there are no changes in the frame. That is, for example, out of ten or hundreds of identical frames, all are saved, although only one is sufficient.
Compression between frames works on the opposite principle: when a signal is processed, the entire video image is analyzed, but only key changes are saved, for example the movement of an object, while the background and surrounding environment of the object remain the same. This allows you to significantly reduce the size of the video file compared to frame-by-frame compression.
However, even the most advanced video compression algorithms degrade the quality of the original image. It is true that today codecs have appeared that compress video in such a way that there is practically no loss of quality.
In this case, compression takes into account: video resolution, file size, method of transferring and downloading a video file, predominance of static or dynamic scenes, color, contrast, etc. The quality and size of the resulting video file depend on the codec used.
But that’s not all, because the file obtained when recording video from surveillance cameras must not only be compressed and encoded, it must, if necessary, be decompressed and decoded, and for this it is better to use the same codec as for the compression.
Currently, there are several important compression standards used in video surveillance. Consider them in more detail.
Compression standard M-JPEG (Motion JPEG)
It is a license-free encoding standard created and widely used in the 1990s. It uses intra-frame compression technology. The digital video sequence obtained with this codec is a full weight JPEG image matrix. Although this codec allows the use of a number of tools that reduce file size, today it is rarely used due to the low quality of the resulting image, as well as the minimum video compression ratio.
MPEG-4 compression standard
Licensed coding standard that uses object-oriented compression (between frames), that is, when the movement of each object in the frame is tracked separately and based on these movements, the video signal is recorded. The main advantage of this codec is the wide range of compression ratio settings that can be selected for any data transfer rate. This format is universal and is used to view sweat videos in real time. However, this standard is already out of date.
H.264 and H.264 + compression standards
Newer licensed encoding standards that significantly reduce the size of a digital video file. These codecs make minimal changes to video image quality and are designed to record video signals for a long time, as they require little network bandwidth and hard drive space.
The H.264 codec is one of the best tools for working in video surveillance systems, especially when shooting at high frame rates and high resolutions.
