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2.2 MPEG stream

(1) What is MPEG

MPEG is an international standard for video compression and compresses video to 1.5Mbit / sec. Image data is compressed to approximately 1/50 and audio data is compressed to approximately 1/10, and can be recorded on a standard speed CD.

(2) Picture type

The following three types of pictures are composed of video compression methods.

Table 2.2 Picture types 
 Picture type 
 Description 
 I picture 
 (Intra-coded Picture) 
 An image that can be decoded only from its own information. Although compression efficiency is poor, random access is also possible if this image is inserted at regular intervals. 
 P picture 
 (Predictive-coded Picture) 
 Other pictures already decoded as predicted images < 
 Images that use cha (I, P). 
 B picture 
 (Bidirectionally 
 predictive-coded picture) 
 Predicted picture Images to use 
 I, P). The compression efficiency is the best.


Figure 2.1 Predictive relationship between pictures

(3) GOP

GOP (Group Of Picture) is composed of one or more I pictures and zero or more non-I pictures. GOP is a basic editing unit and can be played independently.

∙ In order to decode a B picture, the I picture or P picture that is the predicted picture must be decoded first. Therefore, the order in which pictures are input to the decoder and the actual display order are changed.

Figure 2.2 Order on CD-ROM and playback image order

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