Function segment_available_from_ticks 

pub fn segment_available_from_ticks(
    ast_us: i128,
    period_start_us: i128,
    start_ticks: i128,
    duration_ticks: i128,
    timescale: u64,
    ato_us: i128,
) -> i128

segment_available_from for a segment given in ticks: the end of the segment (MPDstart + MPDduration) is converted once, so rounding never accumulates.