nstraints if it were activated by reference in an otherwise-conforming bitstream. During operation of the decoding process (see clause 8), the values of parameters of the active picture parameter set and the active sequence parameter set shall be considered in effect. For interpretation of SEI messages, the values of the parameters of the picture parameter set and sequence parameter set that are active for the operation of the decoding process for the VCL NAL units of the primary coded picture in the same access unit shall be considered in effect unless otherwise specified in the SEI message semantics. 7.4.1.2.2 Order of access units and association to coded video sequences A bitstream conforming to this Recommendation International Standard consists of one or more coded video sequences. A coded video sequence consists of one or more access units. For coded video sequences that conform to one or more of the profiles specified in Annex A and are decoded using the decoding process specified in clauses 2-9, the order of NAL units and coded pictures and their association to access units is described in clause 7.4.1.2.3. The first access unit of each coded video sequence is an IDR access unit. All subsequent access units in the coded video sequence are non-IDR access units. It is a requirement of bitstream conformance that, when two consecutive access units in decoding order within a coded video sequence both contain non-reference pictures, the value of picture order count for each coded field or field of a coded frame in the first such access unit shall be less than or equal to the value of picture order count for each coded field or field of a coded frame in the second such access unit. It is a requirement of bitstream conformance that, when present, an access unit following an access unit that contains an end of sequence NAL unit shall be an IDR access unit. It is a requirement of bitstream conformance that, when an SEI NAL unit contains data that pertain to more than one access unit (for example, when the SEI NAL 