Compare sdp to determine if transcoding is being used. (#1444)

* compare sdp for transcoding

* refactor sdp check for leading codec

* fix reference to epOther

* minor changes

* minor

* fix #1447

* fix security issue

* use convenience getter appIsUsingWebsockets in CallSession

---------

Co-authored-by: Dave Horton <daveh@beachdognet.com>

lib/utils/sdp-utils.js

@@ -55,11 +55,28 @@ const extractSdpMedia = (sdp) => {
   }
 };
 
+const getLeadingCodec = (sdp) => {
+  if (!sdp) {
+    return null;
+  }
+
+  const parsed = sdpTransform.parse(sdp);
+  const audio = parsed.media?.find((m) => m.type === 'audio');
+
+  if (!audio) {
+    return null;
+  }
+
+  return audio.rtp?.[0]?.codec || null;
+};
+
+
 module.exports = {
   isOnhold,
   mergeSdpMedia,
   extractSdpMedia,
   isOpusFirst,
   makeOpusFirst,
-  removeVideoSdp
+  removeVideoSdp,
+  getLeadingCodec
 };