Capture encrypted VoIP calls with Wireshark ?

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Is there a way to send you the .pcap file, may be to PM or email? These files usually contain too much specific data to post them on a public forum unedited. I doubt TextNow uses their own protocol since this app allows to call any other softphones, ATAs, mobiles and landlines.

Thanks for the feedback. I think you're right regarding the cloud infrastructure and protocol exchange gateway. Does that mean Wireshark looses some ground in capturing and analyzing modern VoIP traffic? In that regard, what package would you suggest to capture and listen to this traffic? Also, any VoIP Recording package you know allows to capture a single call randomly directed by Windows via several NICs at different call stages, even if not encrypted like this?

Well, the very idea of encryption is that witty folks using Wireshark (or anything else for that matter) would not be able to record the calls and listen to them.

So if you can get the TLS sessions' secrets from your browser, you can decrypt your own TLS sessions (unless DH key negotiation was used), but without that data - game over. If the app is self-sufficient, i.e. doesn't run in browser window, you'll not be able to decipher even your own calls.

Which brings me to an idea that the codec used might have actually been Opus but the RTP may have been an SRTP in fact - the two are indistinguishable as the only difference is the payload, so only the signalling information could tell whether SRTP was used or not.