def time_format( t ) :
    """
    Produces the time format expected by the srt format,
    given a parameter t representing a number of seconds.
    """
    hours = int(t/3600)
    minutes = int((t-hours*3600)/60)
    seconds = int(t-hours*3600-minutes*60)
    fraction = int((t%1)*100)
    return str(hours) + ":" + str(minutes) + ":" + str(seconds) + "." + str(fraction)