Sure. The entirety of the original Matrix team used to be a team called “next gen telephony” inside a startup called MX Telecom, which then got acquired by Amdocs and turned into their Unified Communications division, which I ran. The product was a horizontally scalable SIP softswitch built on resiprocate (B2BUA SBC and stateless router components), and then with media processing done using a C++ media graph framework we created called mxmedia. This was similar to gstreamer, but with more flexible threading and using C++ typing extensively to model media formats and propagate them through the media graph. It ended up with roughly the same featureset as today’s gstreamer, but about 10 years earlier - so with muxers, demuxers, packetizers, codecs, resamplers, colourspace transforms, AEC, AGC, rate control, SRTP, ICE, etc. We used it serverside for media gateways for transcoding calls for ISDN, H.323 and IAX; we then ported it clientside when smartphones came around to use it as a webrtc-style softphone SDK.
Unfortunately the IP was all proprietary and owned by the company, and when WebRTC stole our lunch we shifted focus to messaging and building Matrix, and have slowly returned focus to VoIP - hence Element Call.