bintime_addx
bintime_addx(&bt, pps->capth->th_scale * (acount - pps->capth->th_offset_count));
bintime_addx(&bt, pps->capth->th_scale * dcount);
bintime_addx(&bt, scale * tcount);
bintime_addx(bt, th->th_scale * tc_delta(th));
bintime_addx(&th->th_offset, th->th_scale * delta);