Function segment_available_until 

pub fn segment_available_until(
    ast_us: i128,
    period_start_us: i128,
    mpd_start_us: i128,
    mpd_duration_us: i128,
    tsb_us: Option<i128>,
) -> Option<i128>

Availability end of a Media Segment; None without a time-shift buffer depth (the segment never leaves the window).