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group of pictures (GOP)

 

A major feature of MPEG-2 encoding is its ability to remove redundancy, not only within a frame, but also among a group of frames. MPEG-2 uses three frame types (I, P, and B) to represent the video.

A group of pictures (GOP) setting defines the pattern of the three frame types used. These three picture types are defined in the following ways.

Intra (I): Also known as the key frame. Every GOP contains one I-frame. The I-frame is the only MPEG-2 frame type which can be fully decompressed without any reference to frames that precede or follow it. It is also the most data-heavy, requiring the most disk space.

Predicted (P): Encoded from a “predicted” picture based on the closest preceding I- or P-frame. P-frames typically require much less disk space than do I-frames because they reference a preceding I- or P-frame in the GOP.

Note: Both I-frames and P-frames are also known as reference frames, because a B-frame may refer to either one or both frame types.

Bi-directional (B): Encoded from an interpolation of succeeding and preceding reference frames, either I-frame or P-frame. B-frames are the most storage-efficient MPEG-2 frame type, requiring the least amount of disk space.

 


 

 

 

 

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