 set differs from that of the previously-active sequence parameter set, the variable lastFieldBottom is set equal to "not determined". After the output of each picture, the value of lastFieldBottom is checked and set as follows, using the values of field_pic_flag, bottom_field_flag, pic_struct, TopFieldOrderCnt and BottomFieldOrderCnt (when applicable) for the picture that was output. If field_pic_flag is equal to 1, it is a requirement of bitstream conformance that the value of lastFieldBottom shall not be equal to bottom_field_flag. The value of lastFieldBottom is then set equal to bottom_field_flag. Otherwise (field_pic_flag is equal to 0), the following applies: If pic_struct is present and is equal to 3 or 5, it is a requirement of bitstream conformance that the value of lastFieldBottom shall not be equal to 0. The value of lastFieldBottom is then set equal to 1 - ( ( pic_struct -1)>>2). Otherwise, if pic struct is present and is equal to 4 or 6, it is a requirement of bitstream conformance that the value of lastFieldBottom shall not be equal to 1. The value of lastFieldBottom is then set equal to ((pic_struct-1)>>2). Rec. ITU-T H.264 (01/2012) Otherwise, if TopFieldOrderCnt is less than BottomFieldOrderCnt, it is a requirement of bitstream conformance that the value of lastFieldBottom shall not be equal to 0. The value of lastFieldBottom is then set equal to 1. Otherwise, if TopFieldOrderCnt is greater than BottomFieldOrderCnt, it is a requirement of bitstream conformance that the value of lastFieldBottom shall not be equal to 1. The value of lastFieldBottom is then set equal to 0. Otherwise (TopFieldOrderCnt is equal to BottomFieldOrderCnt and pic_struct is not present or is not in the range of 3 to 6, inclusive), lastFieldBottom may have any value, and its value is not changed. NumClockTS is determined by pic_struct as specified in Table D-1. There are up to NumClockTS sets of clock timestamp information for a picture, as specified by clock_timestamp_flag[ i ] for each set. The sets of clock timestamp inf