llowing additional constraints shall be obeyed: Each NAL unit with nal_unit_type equal to 1 or 5 shall be immediately preceded by a prefix NAL unit. In bitstreams conforming to this Recommendation | International Standard, each prefix NAL unit shall be immediately followed by a NAL unit with nal_unit_type equal to 1 or 5. G.7.4.1.2.4 Detection of the first VCL NAL unit of a primary coded picture This clause specifies constraints on VCL NAL unit syntax that are sufficient to enable the detection of the first VCL NAL unit of each primary coded picture. The first VCL NAL unit of the primary coded picture of the current access unit, in decoding order, shall be different from the last VCL NAL unit of the primary coded picture of the previous access unit, in decoding order, in one or more of the following ways: dependency id of the first VCL NAL unit of the primary coded picture of the current access unit is less than dependency_id of the last VCL NAL unit of the primary coded picture of the previous access unit dependency_i of the first VCL NAL unit of the primary coded picture of the current access unit is equal to dependency_id of the last VCL NAL unit of the primary coded picture of the previous access unit and any of the following conditions are true quality id of the first VCL NAL unit of the primary coded picture of the current access unit is less than quality of the last VCL NAL unit of the primary coded picture of the previous access unit quality id of the first VCL NAL unit of the primary coded picture of the current access unit and the last VCL NAL unit of the primary coded picture of the previous access unit is equal to 0, and any of the conditions specified in clause 7.4.1.2.4 is fulfilled G.7.4.1.2.5 Order of VCL NAL units and association to coded pictures Each VCL NAL unit is part of a coded picture. Let dId be the value of dependency id and let qId be the value of quality_i id of any particular VCL NAL unit. The order of the VCL NAL units within a coded picture is constrained as follows: For all VCL NAL