Find function webRtcPlayerObj.onWebRtcOffer in app.js file, add removeExtmapAllowMixed(offer); in the beginning of IF. Then add function removeExtmapAllowMixed(desc) to remove a=extmap-allow-mixed

UE4 Pixel Strimming fix Chrome bug.js

	webRtcPlayerObj.onWebRtcOffer = function (offer) {
		if (ws && ws.readyState === WS_OPEN_STATE) {
			removeExtmapAllowMixed(offer);
			let offerStr = JSON.stringify(offer);
			console.log(`-> SS: offer:\n${offerStr}`);
			ws.send(offerStr);
		}
	};

	function removeExtmapAllowMixed(desc) {
		/* remove a=extmap-allow-mixed for webrtc.org 1 < M71 */
		if (!window.RTCPeerConnection) {
			return;
		}

		if(desc.sdp.indexOf('\na=extmap-allow-mixed') !== -1){
			const sdp = desc.sdp.split('\n').filter((line) => {
				return line.trim() !== 'a=extmap-allow-mixed';
			}).join('\n');
			desc.sdp = sdp;
			return sdp;
		}
	};