def convert_millis(track_dur_lst):
    """ Convert milliseconds to 00:00:00 format """
    
    converted_track_times = []
    for track_dur in track_dur_lst:
        seconds = (int(track_dur)/1000)%60
        minutes = int(int(track_dur)/60000)
        hours = int(int(track_dur)/(60000*60))
        converted_time = '%02d:%02d:%02d' % (hours, minutes, seconds)
        converted_track_times.append(converted_time)    
    return converted_track_times