Video compression methods are used in network CCTV surveillance systems to improve the efficiency of transmission and reduce the need for more expensive storage. Most manufacturers use standard compression techniques to ensure compatibility and interoperability.
There are three standards of video compression: Motion JPEG, MPEG-4, and H.264. The latter is the latest standard and is considered to be the most efficient and most widely adopted. Each option has different qualities so it is important to understand the technology to select the best method for a specific application.
Motion JPEG (MJPEG) compresses each of the video frames in a sequence separately using the JPEG format. In doing so, it guarantees the same quality for each image so that the compression ratio of MJPEG is relatively low compared to interframe compression standards (such as MPEG4 and H.264). Since there is no dependency between the frames, a Motion JPEG video is robust and can afford to lose frames during transmission without affecting the rest of the video.
MPEG-4 is a licensed standard, so users pay a fee for each monitoring station. MPEG-4 supports low-bandwidth applications and high-quality images. As it is an interframe video that compresses only the differences between frames in a video sequence, it results in a better compression ratio than MJPEG. This means there are no limitations in frame rate and almost unlimited bandwidth. The advantage for MPEG-4 files compared with Motion JPEG files is the reduced bandwidth and storage requirements, which in turn, generates cost savings. The downside of MPEG-4, as a more complex compression system, is greater latency before video can be viewed. It also needs to be a higher specification (and therefore cost) to decode the MPEG4 video.
H.264 is the latest MPEG standard for video encoding and it is expected to be the main video compression standard in the future. H.264 can maintain image quality, reduce the size of a digital file by as much as 80% (vs Motion JPEG) and as much as 50% when compared with the MPEG-4 standard. This means much less network bandwidth is used and lower storage space is required. The downside of H.264 is that other hardware in the systems, such as cameras and monitoring stations, need to be higher performance machines, but this now has less of an effect with advances in PC/Server technology.
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