pjsip/pjproject — reverse-engineered prompt

Build me a portable open source VoIP and multimedia communication library like PJSIP. I want a solid C core with simple high level APIs that other apps can use from C, C++, Java, C#, and Python.

It should handle SIP calling, session setup, RTP media, and common network issues like STUN, TURN, ICE, and NAT traversal. Please include the pieces needed for audio and video communication, plus a small sample calling app that can register to a SIP account, make a call, receive a call, and show useful logs.

Make it buildable on Mac, Linux, Windows, Android, and iOS, with clear build instructions and basic tests so I can verify it works. Keep the code organized as a reusable library, not just one demo program. Look up the current PJSIP docs online if you need to match the expected behavior and build flow.