rd_parameters_present_flag,and pic_struct_present_flag for subset sequence parameter set RBSPs is reserved for future use by ITU-T ISO/IEC. When timing_info_present_flag is equal to 1, decoders shall ignore the values of the directly following num_units_in_tick, time_scale, fixed_frame_rate_flag syntax elements. When hal_hrd_parameters_present_flag is equal to 1, decoders shall ignore the value of the syntax elements in the directly following hrd parameters() syntax structure. When vcl_hrd_parameters_present_flagis equal to 1, decoders shall ignore the value of the syntax elements in the directly following rd_parameters() syntax structure. If max_num_ref_frames is included in a sequence parameter set, the semantics specified in clause 7.4.2.1.1 apply. Otherwise (max_num_ref_frames is included in a subset sequence parameter set), the following is specified: max_num_ref_frames specifies the maximum number of short-term and long-term reference frames, complementary reference field pairs, and non-paired reference fields that may be used by the decoding process for inter prediction of any view component in the coded video sequence. max_num_ref_frames also determines the sliding window size of the sliding window operation as specified in clause H.8.3. The value of max_num_ref_frames shall be in the range of 0 to 16, inclusive. H.7.4.2.1.1.1 Scaling list semantics The semantics specified in clause 7.4.2.1.1.1 apply. Rec. ITU-T H.264 (01/2012) H.7.4.2.1.2 Sequence parameter set extension RBSP semantics The semantics specified in clause 7.4.2.1.2 apply. Additionally, the following applies. Sequence parameter set extension RBSPs can only follow sequence parameter set RBSPs in decoding order. Subset sequence parameter set RBSPs shall not be followed by a sequence parameter set extension RBSP. The contents of sequence parameter set extension RBSPs only apply when the base view, which conforms to one or more of the profiles specified in Annex A, of a coded video sequence conforming to one or more profiles specified in Annex H