From 3f2744f0325d30717dbf9131cf7adf19880e39b8 Mon Sep 17 00:00:00 2001
From: Hoan Luu Huu <110280845+xquanluu@users.noreply.github.com>
Date: Thu, 3 Apr 2025 18:58:39 +0700
Subject: [PATCH] fixed replaceEndpoint offer single codec that callee does not
 support (#1131)

---
 lib/session/call-session.js | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/lib/session/call-session.js b/lib/session/call-session.js
index 3292f2d5..8a16689f 100644
--- a/lib/session/call-session.js
+++ b/lib/session/call-session.js
@@ -2354,10 +2354,32 @@ Duration=${duration} `
     // Destroy previous ep if it's still running.
     if (this.ep?.connected) this.ep.destroy();
 
-    this.ep = await this.ms.createEndpoint({remoteSdp: this.dlg.remote.sdp});
+    /* Codec negotiation issue explanation:
+     *
+     * Problem scenario:
+     * 1. Initial negotiation:
+     *    - FreeSWITCH → SBC: offers multiple codecs (PCMU, PCMA, G722)
+     *    - SBC → Callee: passes all codecs (PCMU, PCMA, G722)
+     *    - Callee → SBC: responds with PCMA (its supported codec)
+     *    - SBC → FreeSWITCH: responds with PCMU (after transcoding)
+     *
+     * 2. After endpoint replacement:
+     *    - If we only offer PCMU in the new endpoint
+     *    - FreeSWITCH → SBC: offers only PCMU
+     *    - SBC → Callee: offers only PCMU
+     *    - Call fails: Callee rejects since it only supports PCMA
+     *
+     * Solution:
+     * Always have FreeSWITCH offer multiple codecs to the SBC, don't pass remote sdp here to ensure
+     * the SBC can reoffer the same codecs that the callee originally accepted.
+     * This prevents call failures during media renegotiation.
+     */
+
+    this.ep = await this.ms.createEndpoint();
     this._configMsEndpoint();
 
-    await this.dlg.modify(this.ep.local.sdp);
+    const sdp = await this.dlg.modify(this.ep.local.sdp);
+    await this.ep.modify(sdp);
     this.logger.debug('CallSession:replaceEndpoint completed');
     return this.ep;
   }