Discerning ptime (packetization time) for a given pcap


I would like some help on the subject of an automated way of discerning the average packetization time (ptime) of a VoIP call’s packet capture.

The reason I am not depending on the value in the SDP is because some PBXs that I work with, send their packets not in accordance to the value agreed in the 200 OK SDP. This causes quality issues that I’d rather not have.

I intend to have a script that goes through my pcap files and alerts me if the ptime is not what was agreed upon.

Let me know if I have to make myself clearer - any command line tools, or any method, that I can use to automate the process would be very appreciated.