count simultaneous RTP sessions from live capture/saved pcap with Lua

Currently, I'm looking for a Lua script that would count active RTP sessions on a live tshark capture or on saved pcap files.

Right now, the only way I found is to count RTP packets per second with tshark -qz io,stat and divide by 50 to get actual number of VOIP conversations. However, this requires way too many steps to be realistic on a regular basis other than to troubleshoot specific time ranges.

I was thinking about creating a table/list with SSRC id, where the line count would indicate number of active sessions. Not sure this is the best way though.

Thanks!