s in the slice layer and above: Variables and functions relating to picture order count are derived in clause 8.2.1. (only needed to be invoked for one slice of a picture) Variables and functions relating to the macroblock to slice group map are derived in clause 8.2.2. (only needed to be invoked for one slice of a picture) The method of combining the various slice data partitions when slice data partitioning is used is described in clause 8.2.3. Rec. ITU-T H.264 (01/2012) When the frame_num of the current picture is not equal to PrevRefFrameNum and is not equal to PrevRefFrameNum + 1 % MaxFrameNum, the decoding process for gaps in frame num is performed according to clause 8.2.5.2 prior to the decoding of any slices of the current picture. At the beginning of the decoding process for each P, SP, or B slice, the decoding process for reference picture lists construction specified in clause 8.2.4 is invoked for derivation of reference picture list 0 (RefPicList0), and when decoding a B slice, reference picture list 1 (RefPicList1). When the current picture is a reference picture and after all slices of the current picture have been decoded, the decoded reference picture marking process in clause 8.2.5 specifies how the current picture is used in the decoding process of inter prediction in later decoded pictures. 3. The processes in clauses 8.3, 8.4, 8.5, 8.6, and 8.7 specify decoding processes using syntax elements in the macroblock layer and above. The intra prediction process for I and SI macroblocks, except for I PCM macroblocks as specified in clause 8.3, has intra prediction samples as its output. For I PCM macroblocks clause 8.3 directly specifies a picture construction process. The output are constructed samples prior to the deblocking filter process. The inter prediction process for P and B macroblocks is specified in clause 8.4 with inter prediction samples being the output. The transform coefficient decoding process and picture construction process prior to deblocking filter process are specified in claus