 to 0 in the previous picture in decoding order having the same values of sub_seq_id and sub_seq_layer_num as the current picture, the value of last_pic_flag is equal to 1 in the previous picture in decoding order having the same values of ub_seq_id and sub_seq_layer_num as the current picture. Otherwise, the current picture belongs to the same sub-sequence as the previous picture in decoding order having the same values of sub_seq_id sub_seq_layer_num as the current picture. sub_seq_frame_num_flag equal to 0 specifies that sub_seq_frame_num is not present. sub_seq_frame_num_flage equal to 1 specifies that s ub_seq_frame_num is present. sub_seq_frame_num shall be equal to 0 for the first reference picture of the sub-sequence and for any non-reference picture preceding the first reference picture of the sub-sequence in decoding order. sub_seq_frame_num is further constrained as follows: Rec. ITU-T H.264 (01/2012) If the current picture is not the second field of a complementary field pair, sub_seq_frame_num shall be incremented by 1, in modulo MaxFrameNum operation, relative to the previous reference picture, in decoding order, that belongs to the sub-sequence. Otherwise (the current picture is the second field of a complementary field pair), the value of sub_seq_frame_num shall be the same as the value of sub_seq_frame_num for the first field of the complementary field pair. sub_seq_frame_num shall be in the range of 0 to MaxFrameNum - 1, inclusive. When the current picture is an IDR picture, it shall start a new sub-sequence in sub-sequence layer 0. Thus, the sub_seq_layer_num shall be 0, the sub_seq_id shall be different from the previous sub-sequence in sub-sequence layer 0, first_ref_pic_flag shall be 1, and leading_non_ref_pic_flagshall be equal to 0. When the sub-sequence information SEI message is present for both coded fields of a complementary field pair, the values of sub_seq_layer_num, sub_seq_id, leading_non_ref_pic_flag and sub_seq_frame_num, when present, shall be the same for both of these pictures