set amr's bitrate

src/avprofile.c

@@ -373,7 +373,7 @@ PayloadType payload_type_amr={
 	BITS_PER_SAMPLE(0),
 	ZERO_PATTERN(NULL),
 	PATTERN_LENGTH(0),
-	NORMAL_BITRATE(0),
+	NORMAL_BITRATE(12200),
 	MIME_TYPE ("AMR"),
 	CHANNELS(1)
 };