D-Link DCS-1100 - mydlink-enabled Wired Network Camera Uživatelský manuál stáhnout pdf (Strana 24)

Video Compression

 Uncompressed or raw video data consumes very large amount of data

storage and requires high bandwidth to transmit.

 Video compression is a technique to reduce or remove some quantity of

video data with acceptable quality so that the digital video can be stored or

sent in an efficient size.

 There are many compression technologies available in the market which

may be proprietary or following industry standard. Most network vendors

use standard compression technique to ensure compatibility and

interoperability.

IP Surveillance Essential

• Compression

Video Codec

 Video Codec (encoder/decoder) is a pair of algorithms used for

compressing and/or decompressing digital video.

 Different algorithms can be implemented in the same hardware or software

which will allow multiple formats to coexist. Different algorithms however

may not be compatible with each other, and video compressed with one

algorithm usually cannot be decompressed using a different algorithm.

 Some of the commonly used video codec include:

• MPEG-1 : used for Video CDs

• MPEG-2 : used for DVD, SVCD and most digital video broadcasting and cable

distribution system

• MPEG-4 : used for Internet, broadcast and storage media

• WMV: Microsoft’s family of video codec designs

IP Surveillance Essential

• Compression

Motion JPEG

 Motion JPEG is a digital video sequence format that consist of a series of

individual JPEG image. A series of image frames is considered as a motion

video if 16 image frames or more are shown in one second. 30 (NTSC) or

25 (PAL) frames per second will be recognized as full motion video.

 Each image frame in the video sequence should have the same quality

depending on the compression level. The higher the compression level, the

lower the image quality and file size.

IP Surveillance Essential

• Compression

Frame 1 Frame 2

Frame 3

MPEG-4

 MPEG-4 is one of the licensed standard developed by MPEG (Moving Picture

Experts Group), a committee formed by ISO to set standard for audio and video

compression.

 One of the main advantage of MPEG-4 is that MPEG-4 offers high quality image with

minimum file size thus MPEG-4 is suitable for low bandwidth application that requires

high quality images.

 MPEG-4 uses an algorithm that compares a frame with its reference frame and only

pixels that are different from the reference frame are coded.

IP Surveillance Essential

• Compression

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