Prediction Coding - Advanced Video Coding Systems - page 74

Fig. 4.17 Hierarchical B coding structure of GOP in size 4 ( a )andsize8( b )

reference pictures. Figure 4.17 shows hierarchical B structure with GOP size of 4 and
8. More coding structure are provided in Fig. 4.18 , including the hierarchical P, and
hierarchical P/B picture coding, which is more generalized hierarchical reference
coding structure.
To support the flexible coding structure, a flexible reference picture reference
scheme-based on RCS is adopted in AVS2. Through the information in RCS, the
encoder can arbitrarily configure the reference picture set for current coding picture.
RCS consists of reference picture information of current coding picture including
the coding order index (COI), playing order index (POI), quantization parameter
(QP) offset, the number of reference pictures, delta COI between current picture and
reference picture, number of pictures that need to be removed from buffer and delta
COI between pictures from buffer and current picture.
The COI is used to represent the coding order of current picture and reference
pictures. And playing order index (POI) is used to represent the playing order of
current picture and reference pictures. QP offset is used to set the QP of current
coding picture. And the number of reference pictures and the delta COI between
current picture and reference picture are used to set up reference picture set for
current picture. Meanwhile, the number of pictures that need to be removed from
buffer and delta COI between pictures from buffer and current picture are used to
manage DPB. At the encoder side the syntax element coi is used to transmit the COI
of current picture. And coi is defined as

coi = COI%256 . (4.45)