ified in the active sequence parameter set for the pictures, the two fields of the complementary reference field pair are output together, and both fields of the complementary reference field pair are marked as "not needed for output". The frame buffer that included the picture or complementary reference field pair that was cropped and output is checked, and when any of the following conditions are true, the frame buffer is emptied and the DPB fullness is decremented by 1: The frame buffer contains a non-reference non-paired field. The frame buffer contains a non-reference frame. The frame buffer contains a complementary non-reference field pair with both fields marked as "not needed for output". The frame buffer contains a non-paired reference field marked as "unused for reference". The frame buffer contains a reference frame with both fields marked as "unused for reference". The frame buffer contains a complementary reference field pair with both fields marked as "unused for reference" and "not needed for output". Rec. ITU-T H.264 (01/2012) Annex D Supplemental enhancement information (This annex forms an integral part of this Recommendation | International Standard.) This annex specifies syntax and semantics for SEI message payloads. SEI messages assist in processes related to decoding, display or other purposes. However, SEI messages are not required for constructing the luma or chroma samples by the decoding process. Conforming decoders are not required to process this information for output order conformance to this Recommendation | International Standard (see Annex C for the specification of conformance). Some SEI message information is required to check bitstream conformance and for output timing decoder conformance. In Annex D, specification for presence of SEI messages are also satisfied when those messages (or some subset of them) are conveyed to decoders (or to the HRD) by other means not specified by this Recommendation | International Standard. When present in the bitstream, SEI messages shall obey 