--- main/rtp_engine.c	(Asterisk 13.6.0)
+++ main/rtp_engine.c	(working copy)
@@ -652,7 +652,7 @@
 	}
 
 	ast_rwlock_rdlock(&static_RTP_PT_lock);
-	new_type = ao2_bump(static_RTP_PT[payload]);
+	new_type = static_RTP_PT[payload];
 	ast_rwlock_unlock(&static_RTP_PT_lock);
 	if (!new_type) {
 		ast_debug(1, "Don't have a default tx payload type %d format for m type on %p\n",
@@ -663,6 +663,29 @@
 	ast_debug(1, "Setting tx payload type %d based on m type on %p\n",
 		payload, codecs);
 
+	if (new_type->format) {
+		struct ast_format *new_format = ast_format_parse_sdp_fmtp(new_type->format, "");
+
+		if (new_type->format != new_format) {
+			struct ast_rtp_payload_type *tmp_type = ast_rtp_engine_alloc_payload_type();
+
+			if (!tmp_type) {
+				ao2_ref(new_format, -1);
+				return;
+			}
+			tmp_type->asterisk_format = new_type->asterisk_format;
+			tmp_type->rtp_code = new_type->rtp_code;
+			tmp_type->payload = payload;
+			tmp_type->format = new_format;
+			new_type = tmp_type;
+		} else {
+			ao2_ref(new_format, -1);
+			new_type = ao2_bump(new_type);
+		}
+	} else {
+		new_type = ao2_bump(new_type);
+	}
+
 	ast_rwlock_wrlock(&codecs->codecs_lock);
 
 	if (payload < AST_VECTOR_SIZE(&codecs->payloads)) {