[Mp4-tech] Question regarding initialisation of context variable when performing CABAC decoding

[Lin David]

Greetings,
(Sorry if the similar question had been raised before)
I would be grateful if someone could shed lights to me regarding the
"initialisation of context variables" (in Figure 9-1 and section 9.3.1.1
Initialisation process for context variables) when performing CABAC
decoding. 
Assuming that I'm doing the syntax element, mb_skip_flag, decode under
B-slice, so I would have the ctxIdx vale ranges between 24-26 (according
to Table 9-11) for initialisation (I could be wrong here). 
Then I need to refer to Table 9-14 and based on the value of
cabac_init_idc (0/1/2) to select the m and n values for doing the
process defined in section 9.3.1.1. 
Since there are three possibilities here for ctxIdx value (between
24-26), could anyone hint me which one I should use for initialisation
(ctxIdx = 24, 25, or 26)? Or any value between 24-26 for ctxIdx would be
fine when retrieving the m and n values. 
Thank you in advance.
Best Regards,
David Lin
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