bugfix: rtpengine needs to transcode when different codecs are used on A and B legs

lib/utils/strip-ancillary-codecs.js

@@ -0,0 +1,30 @@
+const sdpTransform = require('sdp-transform');
+
+const stripCodecs = (logger, remoteSdp, localSdp) => {
+  try {
+    const sdp = sdpTransform.parse(remoteSdp);
+    const local = sdpTransform.parse(localSdp);
+    const m = local.media
+      .find((m) => 'audio' === m.type);
+    const pt = m.rtp[0].payload;
+
+    /* manipulate on the audio section */
+    const audio = sdp.media.find((m) => 'audio' === m.type);
+
+    /* discard all of the codecs except the first in our 200 OK, and telephony-events */
+    const ptSaves = audio.rtp
+      .filter((r) => r.codec === 'telephone-event' || r.payload === pt)
+      .map((r) => r.payload);
+    const rtp = audio.rtp.filter((r) => ptSaves.includes(r.payload));
+
+    /* reattach the new rtp sections and  stripped payload list */
+    audio.rtp = rtp;
+    audio.payloads = rtp.map((r) => r.payload).join(' ');
+    return sdpTransform.write(sdp);
+  } catch (err) {
+    logger.error({err, remoteSdp, localSdp}, 'strip-ancillary-codecs error');
+  }
+};
+
+module.exports = stripCodecs;
+