def _parse_ts(ts):
    """
    Convert a parsed WebVTT timestamp (a re.Match obtained from _REGEX_TS)
    into an MPEG PES timestamp: a tick counter at 90 kHz resolution.
    """
    return 90 * sum(
        int(part or 0) * mult for part, mult in zip(ts.groups(), (3600_000, 60_000, 1000, 1)))