split large ros bag to small bag

rosbag_split.py

#!/usr/bin/env python

import rosbag
import os
from shutil import copyfile
import glob

bags_path = glob.glob('/home/aaa/dataset/*.bag')
for bag_file in bags_path:
    bag = rosbag.Bag(bag_file)
    bag_prefix = bag_file.split('.bag')[0]+'_'
    time_step = 50

    print "Reading bag. Please wait..."
    it = bag.read_messages()
    last_ts = bag.get_start_time()
    index = 1 
    print "Reading done!"

    tag = str(index).zfill(3)
    bag_dir = bag_prefix+tag

    wbag = rosbag.Bag(bag_dir+'.bag', 'w')
    for msg in it:
        ts = msg.timestamp
        ts = ts.to_sec()
        if (ts-last_ts) > time_step:
            wbag.close()
            print 'Bag # '+str(index)+' written.'
            index += 1
            tag = str(index).zfill(3)
            bag_dir = bag_prefix+tag
            print('write: {}'.format(bag_dir+'.bag'))
            wbag = rosbag.Bag(bag_dir+'.bag', 'w')
            last_ts = ts

        wbag.write(msg.topic, msg.message, msg.timestamp)

    wbag.close()