 second_scene_id is the same as the value of scene id of the next picture in output order, this indicates that the encoder considers one of the source scenes for the target pictures and the source scene for the next picture (in output order) to have been the same scene. When the value of second is not equal to the value of scene id or second_scene_id (if present) of the next picture in output order, this indicates that the encoder considers the target pictures and the next picture (in output order) to have been from different source scenes. When the value of scene_id of a picture is equal to the value of scene id of the following picture in output order and the value of scene_transition_type in both of these pictures is less than 4, this indicates that the encoder considers the two pictures to have been from the same source scene. When the values of scene_id, scene_transition_type and second_scene_id(if present) of a picture are equal to the values of scene id, scene_transition_type and (respectively) of the following picture in output order and the value of scene_transition_type is greater than 0, this indicates that the encoder considers the two pictures to have been from the same source gradual scene transition. The value of second_scene_id shall be in the range of 0 to 232 2, inclusive. Values of second_scene_id in the range of 0 to 255, inclusive, and in the range of 512 to 231 - 1, inclusive, may be used as determined by the application. Values of second scene id in the range of 256 to 511, inclusive, and in the range of 231 to 232 - 2, inclusive, are reserved for future use by ITU-T ISO/IEC. Decoders encountering a value of second_scene_id in the range of 256 to 511, inclusive, or in the range of 231 to 232 2, inclusive, shall ignore (remove from the bitstream and discard) it. D.2.11 Sub-sequence information SEI message semantics The sub-sequence information SEI message is used to indicate the position of a picture in data dependency hierarchy that consists of sub-sequence layers and sub-sequences. A sub-s