 PCM. Rec. ITU-T H.264 (01/2012) 9.3.1.1 Initialisation process for context variables Outputs of this process are the initialised CABAC context variables indexed by ctxIdx. Tables 9-12 to 9-33 contain the values of the variables n and m used in the initialisation of context variables that are assigned to all syntax elements in clauses 7.3.4 and 7.3.5 except for the end-of-slice flag. For each context variable, the two variables pStateIdx and valMPS are initialised. NOTE 1 - The variable pStateIdx corresponds to a probability state index and the variable valMPS corresponds to the value of the most probable symbol as further described in clause 9.3.3.2. The two values assigned to pStateIdx and valMPS for the initialisation are derived from SliceQPy, which is derived in Equation 7-29. Given the two table entries (m,n), the initialisation is specified by the following pseudo-code process: preCtxState=Clip3(1,126,((m*Clip3(0,51,SliceQPy))>>4 = +n) if( preCtxState <= 63 ) { pStateIdx = 63 - preCtxState valMPS = 0 (9-5) } else { pStateIdx = preCtxState - 64 valMPS = 1 In Table 9-11, the ctxIdx for which initialisation is needed for each of the slice types are listed. Also listed is the table number that includes the values of m and n needed for the initialisation. For P, SP and B slice type, the initialisation depends also on the value of the cabac_init_idc syntax element. Note that the syntax element names do not affect the initialisation process. Rec. ITU-T H.264 (01/2012) Table 9-11 - Association of ctxIdx and syntax elements for each slice type in the initialisation process Slice type Syntax element Table P, SP Table 9-13 mb_skip_flag 11..13 24..26 Table 9-14 slice_data() mb_field_decoding_flag Table 9-18 70..72 70..72 70..72 70..72 Table 9-12 mb_type Table 9-13 0..10 3..10 14..20 27..35 Table 9-14 transform_size_8x8_flag Table 9-16 399..401 399..401 399..401 macroblock_layer() coded_block_pattern(luma) Table 9-18 73..76 73..76 73..76 73..76 coded_block_pattern(chro Table 9-18 77..84 77..84 77..84 77..84 mb_qp_delta