Usando python adorável de maneira preguiçosa:
# apt-get install python-pypcap
>>> import pcap
>>> p = pcap.pcap(name="hs22v-boot.pcap")
>>> packets = [x for x in p]
>>> duration = packets[-1][0] - packets[0][0]
>>> totalbytes = sum([len(x[1]) for x in packets])
>>> numpackets = len(packets)
>>> duration, totalbytes, numpackets
(113.37264108657837, 193812281, 227491)