 Sub-sequence characteristics SEI message semantics The sub-sequence characteristics SEI message indicates the characteristics of a sub-sequence. It also indicates inter prediction dependencies between sub-sequences. This message shall be contained in the first access unit in decoding order of the sub-sequence to which the sub-sequence characteristics SEI message applies. This sub-sequence is herein called the target sub-sequence. sub_seq_layer_num identifies the sub-sequence layer number of the target sub-sequence. sub_seq_layer_num shall be in the range of 0 to 255, inclusive. sub_seq_id identifies the target sub-sequence. sub_seq_id shall be in the range of 0 to 65535, inclusive. duration_flag equal to 0 indicates that the duration of the target sub-sequence is not specified. sub_seq_duration specifies the duration of the target sub-sequence in clock ticks of a 90-kHz clock. average_rate_flag equal to 0 indicates that the average bit rate and the average frame rate of the target sub-sequence are unspecified. accurate_statistics_flag indicates how reliable the values of average_bit_rate and average_frame_rate are. accurate_statistics_flag equal to 1, indicates that the average_bit_rate and the average_frame_rate are rounded from statistically correct values. accurate_statistics_flag equal to 0 indicates that the average_bit_rate and the average_frame_rate are estimates and may deviate from the statistically correct values. average_bit_rate indicates the average bit rate in (1000 bits)/second of the target sub-sequence. All NAL units of the target sub-sequence are taken into account in the calculation. The average bit rate is derived according to the access unit removal time specified in clause C.1.2. In the following, nB is the number of bits in all NAL units in the sub-sequence. t1 is the removal time (in seconds) of the first access unit of the sub-sequence (in decoding order), and t2 is the removal time (in seconds) of the last access unit of the sub-sequence (in decoding order). When accurate_statistics_fla