of an IDR access unit is preceded by a buffering period SEI message within the same access unit, the activation of the associated sequence parameter set (and, for IDR pictures that are not the first picture in the bitstream, the determination that the primary coded picture is an IDR picture) does not occur until the decoding of the first coded slice NAL unit of the primary coded picture. Since the coded slice NAL unit of the primary coded picture follows the picture timing SEI message in NAL unit order, there may be cases in which it is necessary for a decoder to store the RBSP containing the picture timing SEI message until determining the parameters of the sequence parameter that will be active for the primary coded picture, and then perform the parsing of the picture timing SEI message. The presence of the picture timing SEI message in the bitstream is specified as follows: IfCpbDpbDelaysPresentFlag is equal to 1 or pic_struct_present_flag is equal to 1, one picture timing SEI message shall be present in every access unit of the coded video sequence. Otherwise (CpbDpbDelaysPresentFlag is equal to 0 and pic_struct_present_flag is equal to 0), no picture timing SEI messages shall be present in any access unit of the coded video sequence. cpb_removal_delay specifies how many clock ticks (see clause E.2.1) to wait after removal from the CPB of the access unit associated with the most recent buffering period SEI message in a preceding access unit before removing from the buffer the access unit data associated with the picture timing SEI message. This value is also used to calculate an earliest possible time of arrival of access unit data into the CPB for the HSS, as specified in Annex C. The syntax element is a fixed length code having a length in bits given by cpb_removal_delay_length_minus The cpb_removal_delay is the remainder of a modulo 2(cpb_removal_delay_length_minus1+1) counter. NOTE 2 - The value of cpb_removal_delay_length_minus1 that determines the length (in bits) of the syntax element cpb_removal_dela 