Concerns WebRTC.The remote video didn't playing when peers are not in the same network -

i'm building webrtc chatting web site using java websocket. works fine when users in same network(like using same wifi).but fails work when users aren't in same network environment. what's confusing remote video has src="blob.....".but video refuses play. stun server use stun:stun.l.google.com:19302. can problem related being in china? thank lot reading. project uploaded in site. https://csckaigi.chinanorth.cloudapp.chinacloudapi.cn/kaigi

edit 1: realized site chinese site,so may need vpn access. website presented japanese,so explain how use this. first click つくる button create room , next enter name in chatting room . second user should enter room number(which copied first user,or click room list below.if there's no list,then click link refresh),then enter user's name.finally users suppose linked , see each other.

stun servers not sufficient. need turn server (and no, there no 'free' ones) things work everywhere, around 16% of sessions require this.

see https://testrtc.com/webrtc-api-trace/ in paragraph "example #1 – webrtc app works locally not on different network!"