Chap.3 Video and Audio Compression
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Compression technologies have a major impact on image quality, bandwidth usage, storage space and system
loading. A high compression ratio can significantly reduce file size, and thus cut down bandwidth usage and
storage space. However, a high compression ratio may cause a trade-off between bandwidth and image quality.
3.1 Video Compression
MJPEG, MPEG-4 and H.264 are three major video compression technologies used by the IP surveillance industry.
Each technology has a different compression ratio and is intended for different applications and purposes.
3.1.1 MJPEG
MJPEG (Motion JPEG), announced by JPEG (Joint Photographic Experts Group) in 1992 and approved by ISO in
1994, is a multimedia format that compresses each video frame separately as a JPEG image. The technology is
widely used in DSCs (Digital Still Camera) and other consumer electronics.
Technology
MJPEG compresses the entire image of each frame as a key frame, which is encoded and decoded independently
without referring to the previous or sequential frames. This results in more redundancy in image size.
Figure 3.1 shows each frame is encoded separately by MJPEG, including the motions (the man’s movement) and
the still background (the car).
Chap.3
Figure 3.1 MJPEG encodes each frame entirely
Video and Audio Compression
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