from scapy.all import * 

capture = rdpcap(sys.argv[1]) 

for packet in capture: 
   if packet.haslayer(UDP) and packet.haslayer(IP) and packet.haslayer(Raw): 
      if packet.getlayer(Raw).load == sys.argv[2]: 
         start = packet.time 
      if packet.getlayer(Raw).load == sys.argv[3]: 
         end = packet.time 
         print (end - start)*1000