if enabled, prefer to use h264 (if it exists in the offer)

modules/xmpp/SDPUtil.js

     getMedia: function (sdp, type) {
         return sdp.media.find(m => m.type === type);
     },
+    /**
+     * Sets the given codecName as the preferred codec by
+     *  moving it to the beginning of the payload types
+     *  list (modifies the given mline in place)
+     * @param {object} videoMLine the video mline object from
+     *  an sdp as parsed by transform.parse
+     * @param {string} the name of the preferred codec
+     */
+    preferVideoCodec: function(videoMLine, codecName) {
+        let payloadType = null;
+        videoMLine.rtp.forEach(rtp => {
+            if (rtp.codec === codecName) {
+                payloadType = rtp.payload;
+            }
+        });
+        if (payloadType) {
+            let payloadTypes = videoMLine.payloads.split(" ").map(p => parseInt(p));
+            const payloadIndex = payloadTypes.indexOf(payloadType);
+            payloadTypes.splice(payloadIndex, 1);
+            payloadTypes.unshift(payloadType);
+            videoMLine.payloads = payloadTypes.join(" ");
+        }
+    },
 };
 
 module.exports = SDPUtil;

modules/xmpp/TraceablePeerConnection.js

     description = this.simulcast.mungeRemoteDescription(description);
     this.trace('setRemoteDescription::postTransform (simulcast)', dumpSDP(description));
 
+    if (this.session.room.options.preferH264) {
+        const parsedSdp = transform.parse(description.sdp);
+        const videoMLine = parsedSdp.media.find(m => m.type === "video");
+        SDPUtil.preferVideoCodec(videoMLine, "h264");
+        description.sdp = transform.write(parsedSdp);
+    }
+
     // if we're running on FF, transform to Plan A first.
     if (RTCBrowserType.usesUnifiedPlan()) {
         description.sdp = this.rtxModifier.stripRtx(description.sdp);