This wtkrtc sdk api based WebRTC r67 release version, this native sdk api was written by c/c++, and the files & code directories info as below:

• README.md
  This file.

• webrtc_r67_patch
  The patch for webrtc r67, include video capture, render, and SW/HW OpenH264 codec.

• wtkrtc_linux_mac_loopback
  Loopback test this api at Linux/macOS platform.

• wtkrtc_mediaengine
  VoIP Media Engine client library for Android/iOS paltform, include demo APP.

• wtkrtc_server
  VoIP Media Engine server based asterisk.

• wtkrtc_proxy_server
  VoIP Media Engine proxy server intend to do proxy/nat/p2p, for reduce VoIP Media Engine server's load.

• wtkrtc_conf_server
  VoIP Media Engine conference server for Android/iOS app engine client, both SFU and MCU.

More info please refer to every directory's readme files.

FYI: https://blog.csdn.net/bingdele/article/details/89329191