https://wiki.wireshark.org/Development/LibpcapFileFormat and http://www.cmegroup.com/confluence/display/EPICSANDBOX/MDP+3.0+-+Packet+and+Message+Headers

Decode_pcap_SBE.py

#!/usr/bin/python
from struct import *

with open('cap','rb') as f:
    data = f.read(24)
    globalHeader = unpack('IHHiIII',data)
    print globalHeader
    data = f.read(16)
    while data != "": 
        packetHeader = unpack('IIII', data)

        data = f.read(packetHeader[3])
        if data == "": 
            break
        #Eth 14 bytes, IP 20 bytes, UDP 8 bytes
        sbe = data[42:]
        if len(sbe) > 16: 
            # Seq num, sending time
            sbeHeader = unpack_from('IQ', sbe, 0)
            # message size, block len, template id, schema id, version
            sbeMsg = unpack_from('HHHHH', sbe, 12) 

            if sbeMsg[2] == 32: 
                # transact time, match event indic, MD Entries
                sbeFix = unpack_from('QB', sbe, 22) 
                # px, size, sec id, rpt seq, numof order, price level, update action, entry type
                # block length is 11 so add 10.
                sbeMDEntries = unpack_from('qiiIiBBB', sbe, 32) 
                print sbeMsg, sbeFix, sbeMDEntries
        data = f.read(16)