--- main/format.c	(Asterisk 13.4)
+++ main/format.c	(working copy)
@@ -36,2 +36,3 @@
 #include "asterisk/format.h"
+#include "asterisk/format_cache.h"
 #include "asterisk/astobj2.h"
@@ -134,10 +135,11 @@
 
 int __ast_format_interface_register(const char *codec, const struct ast_format_interface *interface, struct ast_module *mod)
 {
 	SCOPED_AO2WRLOCK(lock, interfaces);
 	struct format_interface *format_interface;
+	struct ast_format *cached;
 
 	if (!interface->format_clone || !interface->format_destroy) {
 		ast_log(LOG_ERROR, "Format interface for codec '%s' does not implement required callbacks\n", codec);
 		return -1;
 	}
@@ -155,10 +157,15 @@
 		return -1;
 	}
 	format_interface->interface = interface;
 	strcpy(format_interface->codec, codec); /* Safe */
 
+	cached = ast_format_cache_get(codec);
+	if (cached) {
+		cached->interface = format_interface->interface;
+	}
+
 	/* Once registered a format interface cannot be unregistered. */
 	ast_module_shutdown_ref(mod);
 	ao2_link_flags(interfaces, format_interface, OBJ_NOLOCK);
 	ao2_ref(format_interface, -1);
 
@@ -281,18 +288,10 @@
 
 struct ast_format *ast_format_attribute_set(const struct ast_format *format, const char *name, const char *value)
 {
 	const struct ast_format_interface *interface = format->interface;
 
-	if (!interface) {
-		struct format_interface *format_interface = ao2_find(interfaces, format->codec->name, OBJ_SEARCH_KEY);
-		if (format_interface) {
-			interface = format_interface->interface;
-			ao2_ref(format_interface, -1);
-		}
-	}
-
 	if (!interface || !interface->format_attribute_set) {
 		return ao2_bump((struct ast_format*)format);
 	}
 
 	return interface->format_attribute_set(format, name, value);
@@ -300,18 +299,10 @@
 
 struct ast_format *ast_format_parse_sdp_fmtp(const struct ast_format *format, const char *attributes)
 {
 	const struct ast_format_interface *interface = format->interface;
 
-	if (!interface) {
-		struct format_interface *format_interface = ao2_find(interfaces, format->codec->name, OBJ_SEARCH_KEY);
-		if (format_interface) {
-			interface = format_interface->interface;
-			ao2_ref(format_interface, -1);
-		}
-	}
-
 	if (!interface || !interface->format_parse_sdp_fmtp) {
 		return ao2_bump((struct ast_format*)format);
 	}
 
 	return interface->format_parse_sdp_fmtp(format, attributes);
--- res/res_format_attr_opus.c	(Asterisk 13.4)
+++ res/res_format_attr_opus.c	(working copy)
@@ -132,11 +132,11 @@
 static void opus_generate_sdp_fmtp(const struct ast_format *format, unsigned int payload, struct ast_str **str)
 {
 	struct opus_attr *attr = ast_format_get_attribute_data(format);
 
 	if (!attr) {
-		return;
+		attr = &default_opus_attr;
 	}
 
 	/* FIXME should we only generate attributes that were explicitly set? */
 	ast_str_append(str, 0,
 				"a=fmtp:%u "
@@ -181,10 +181,18 @@
 	if (!jointformat) {
 		return NULL;
 	}
 	attr_res = ast_format_get_attribute_data(jointformat);
 
+	if (0 == attr1->maxplayrate) {
+		attr_res->maxplayrate = attr2->maxplayrate;
+	} else if (0 == attr2->maxplayrate) {
+		attr_res->maxplayrate = attr1->maxplayrate;
+	} else {
+		attr_res->maxplayrate = MIN(attr1->maxplayrate, attr2->maxplayrate);
+	}
+
 	/* Only do dtx if both sides want it. DTX is a trade off between
 	 * computational complexity and bandwidth. */
 	attr_res->dtx = attr1->dtx && attr2->dtx ? 1 : 0;
 
 	/* Only do FEC if both sides want it.  If a peer specifically requests not