3.4 Error Robustness for Scalable Video and Image Coding

3.4.1 Correlated Frames for Error Robustness

3.4.1.1 Problem Definition and Objectives

Scalable video coding supports efficient coding for both intra-frame and inter-frame [82], [83]. A group of coding pictures (GOP) is described, with a hierarchical structure depicted in Figure 3.39. It is noted that the size of GOP is restricted to a dyadic choice [84], i.e. the power of 2, in order to maintain the scalability feature in a temporal fashion. Each GOP contains a key frame, which is defined at the last picture. The coding option for key frames is determined by the frequency of intra-frame, I_Freq. If the value of I_ Freq is equal to that of GOP size, all the key frames are described as I-frames. Otherwise, P-frame coding is employed for non-intrakey frames. Note that the SVC hierarchical structure does not allow more than one I-frame within a GOP. Thus, non-key pictures are encoded as P-frames or B-frames.

The value of a key frame (presence and quality) for decoding the entire GOP structure is significant. A lost key frame, due to poor channel conditions, results in a dysfunctional decoding outcome for GOP reconstruction. This causes quality degradation, noticeable frame-freezing, and disturbing motion-jerking phenomena [85]. Hence the design of error robustness for the key frames is essential in error-prone transmission to ensure a good quality of service (QoS). The error-concealment strategy supported by the SVC utilizes ...

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