a bitstream or alike may refer to decoding the referred out-of-band data (which may be obtained from out-of-band transmission, signaling, or storage) that is associated with the bitstream or the coded unit, respectively. [0092] A SEI NAL unit may contain one or more SEI messages, which are not required for the decoding of output pictures but may assist in related processes, such as picture output timing, rendering, error detection, error concealment, and resource reservation. Several SEI messages are specified in HEVC, and the user data SEI messages enable organizations and companies to specify SEI messages for their own use. HEVC contains the syntax and semantics for the specified SEI messages but no process for handling the messages in the recipient is defined. Consequently, encoders are required to follow the HEVC standard when they create SEI messages, and decoders conforming to the HEVC standard are not required to process SEI messages for output order conformance. One of the reasons to include the syntax and semantics of SEI messages in HEVC is to allow different system specifications to interpret the supplemental information identically and hence interoperate. It is intended that system specifications can require the use of particular SEI messages both in the encoding end and in the decoding end, and additionally the process for handling particular SEI messages in the recipient can be specified. [0093] In HEVC, there are two types of SEI NAL units, namely the suffix SEI NAL unit and the prefix SEI NAL unit, having a different nal unit type value from each other. The SEI message(s) contained in a suffix SEI NAL unit are associated with the VCL NAL unit preceding, in decoding order, the suffix SEI NAL unit. The SEI message(s) contained in a prefix SEI NAL unit are associated with the VCL NAL unit following, in decoding order, the prefix SEI NAL unit. [0094] A coded picture is a coded representation of a picture. A bitstream may be defined as a sequence of bits, in the form of a NAL unit stream or a byte stream, that forms the representation of coded pictures and associated data forming one or more coded video sequences. A first bitstream may be followed by a second bitstream in the same logical channel, such as in the same file or in the same connection of a communication protocol. An elementary stream (in the context of video coding) may be defined as a sequence of one or more bitstreams. The end of the first bitstream may be indicated by a specific NAL unit, which may be referred to as the end of bitstream (EOB) NAL unit and which is the last NAL unit of the bitstream. [0095] A coded video sequence may be defined as such a sequence of coded pictures in decoding order that is independently decodable and is followed by another coded video sequence or the end of the bitstream or an end of sequence NAL unit.