diff --git a/daemon/codec.c b/daemon/codec.c
index 0fac155d2..28c6cd8a4 100644
--- a/daemon/codec.c
+++ b/daemon/codec.c
@@ -36,6 +36,7 @@ static void __ssrc_handler_free(struct codec_ssrc_handler *p);
 static void __transcode_packet_free(struct transcode_packet *);
 
 static struct rtp_payload_type *__rtp_payload_type_copy(const struct rtp_payload_type *pt);
+static void __rtp_payload_type_dup(struct call *call, struct rtp_payload_type *pt);
 static void __rtp_payload_type_add_name(GHashTable *, struct rtp_payload_type *pt);
 
 
@@ -83,8 +84,9 @@ static void __make_transcoder(struct codec_handler *handler, struct rtp_payload_
 	handler->ssrc_hash = create_ssrc_hash_full(__ssrc_handler_new, (ssrc_free_func_t) __ssrc_handler_free,
 			handler);
 
-	ilog(LOG_DEBUG, "Created transcode context for '" STR_FORMAT "' -> '" STR_FORMAT "'",
-			STR_FMT(&source->encoding), STR_FMT(&dest->encoding));
+	ilog(LOG_DEBUG, "Created transcode context for " STR_FORMAT "/%u/%i -> " STR_FORMAT "/%u/%i",
+			STR_FMT(&source->encoding), source->clock_rate, source->channels,
+			STR_FMT(&dest->encoding), dest->clock_rate, dest->channels);
 
 	return;
 
@@ -304,6 +306,12 @@ static void __transcode_packet_free(struct transcode_packet *p) {
 
 static struct ssrc_entry *__ssrc_handler_new(void *p) {
 	struct codec_handler *h = p;
+
+	ilog(LOG_DEBUG, "Creating SSRC handler to transcode from %s/%u/%i to %s/%u/%i",
+			h->source_pt.codec_def->rtpname, h->source_pt.clock_rate,
+			h->source_pt.channels, h->dest_pt.codec_def->rtpname, h->dest_pt.clock_rate,
+			h->dest_pt.channels);
+
 	struct codec_ssrc_handler *ch = g_slice_alloc0(sizeof(*ch));
 	ch->handler = h;
 	mutex_init(&ch->lock);
@@ -441,13 +449,45 @@ void codec_packet_free(void *pp) {
 
 
 
-static struct rtp_payload_type *codec_make_payload_type(const str *codec) {
+static struct rtp_payload_type *codec_make_dynamic_payload_type(const codec_def_t *dec, struct call *call) {
+	if (dec->default_channels <= 0 || dec->default_clockrate < 0)
+		return NULL;
+
+	struct rtp_payload_type *ret = g_slice_alloc0(sizeof(*ret));
+	ret->payload_type = -1;
+	str_init(&ret->encoding, (char *) dec->rtpname);
+	ret->clock_rate = dec->default_clockrate;
+	ret->channels = dec->default_channels;
+
+	char full_encoding[64];
+	char params[32] = "";
+
+	if (ret->channels > 1) {
+		snprintf(full_encoding, sizeof(full_encoding), "%s/%u/%i", dec->rtpname, ret->clock_rate,
+				ret->channels);
+		snprintf(params, sizeof(params), "%i", ret->channels);
+	}
+	else
+		snprintf(full_encoding, sizeof(full_encoding), "%s/%u", dec->rtpname, ret->clock_rate);
+
+	str_init(&ret->encoding_with_params, full_encoding);
+	str_init(&ret->encoding_parameters, params);
+	ret->format_parameters = STR_EMPTY;
+	ret->codec_def = dec;
+
+	__rtp_payload_type_dup(call, ret);
+	return ret;
+}
+
+
+// XXX allow specifying codec params (e.g. "transcode=opus/16000/1")
+static struct rtp_payload_type *codec_make_payload_type(const str *codec, struct call *call) {
 	const codec_def_t *dec = codec_find(codec);
 	if (!dec)
 		return NULL;
 	const struct rtp_payload_type *rfc_pt = rtp_get_rfc_codec(codec);
 	if (!rfc_pt)
-		return NULL; // XXX amend for other codecs
+		return codec_make_dynamic_payload_type(dec, call);
 
 	struct rtp_payload_type *ret = __rtp_payload_type_copy(rfc_pt);
 	ret->codec_def = dec;
@@ -457,7 +497,7 @@ static struct rtp_payload_type *codec_make_payload_type(const str *codec) {
 
 
 static struct rtp_payload_type *codec_add_payload_type(const str *codec, struct call_media *media) {
-	struct rtp_payload_type *pt = codec_make_payload_type(codec);
+	struct rtp_payload_type *pt = codec_make_payload_type(codec, media->call);
 	if (!pt) {
 		ilog(LOG_WARN, "Codec '" STR_FORMAT "' requested for transcoding is not supported",
 				STR_FMT(codec));
diff --git a/lib/codeclib.c b/lib/codeclib.c
index 1d7fcac19..288f579db 100644
--- a/lib/codeclib.c
+++ b/lib/codeclib.c
@@ -22,15 +22,25 @@
 
 
 
-#define CODEC_DEF_MULT_NAME(ref, id, mult, name) { \
+#define CODEC_DEF_FULL(ref, id, mult, name, clockrate, channels) { \
 	.rtpname = #ref, \
 	.avcodec_id = AV_CODEC_ID_ ## id, \
 	.clockrate_mult = mult, \
 	.avcodec_name = #name, \
+	.default_clockrate = clockrate, \
+	.default_channels = channels, \
 }
+#define CODEC_DEF_MULT_NAME(ref, id, mult, name) CODEC_DEF_FULL(ref, id, mult, name, -1, -1)
+#define CODEC_DEF_MULT_NAME_ENC(ref, id, mult, name, clockrate, channels) \
+	CODEC_DEF_FULL(ref, id, mult, name, clockrate, channels)
 #define CODEC_DEF_MULT(ref, id, mult) CODEC_DEF_MULT_NAME(ref, id, mult, NULL)
+#define CODEC_DEF_MULT_ENC(ref, id, mult, clockrate, channels) \
+	CODEC_DEF_MULT_NAME_ENC(ref, id, mult, NULL, clockrate, channels)
 #define CODEC_DEF_NAME(ref, id, name) CODEC_DEF_MULT_NAME(ref, id, 1, name)
+#define CODEC_DEF_NAME_ENC(ref, id, name, clockrate, channels) \
+	CODEC_DEF_MULT_NAME_ENC(ref, id, 1, name, clockrate, channels)
 #define CODEC_DEF(ref, id) CODEC_DEF_MULT(ref, id, 1)
+#define CODEC_DEF_ENC(ref, id, clockrate, channels) CODEC_DEF_MULT_ENC(ref, id, 1, clockrate, channels)
 
 static const struct codec_def_s codecs[] = {
 	CODEC_DEF(PCMA, PCM_ALAW),
@@ -39,10 +49,10 @@ static const struct codec_def_s codecs[] = {
 	CODEC_DEF_MULT(G722, ADPCM_G722, 2),
 	CODEC_DEF(QCELP, QCELP),
 	CODEC_DEF(G729, G729),
-	CODEC_DEF(speex, SPEEX),
+	CODEC_DEF_ENC(speex, SPEEX, 16000, 1),
 	CODEC_DEF(GSM, GSM),
 	CODEC_DEF(iLBC, ILBC),
-	CODEC_DEF_NAME(opus, OPUS, libopus),
+	CODEC_DEF_NAME_ENC(opus, OPUS, libopus, 48000, 2),
 	CODEC_DEF_NAME(vorbis, VORBIS, libvorbis),
 	CODEC_DEF(ac3, AC3),
 	CODEC_DEF(eac3, EAC3),
diff --git a/lib/codeclib.h b/lib/codeclib.h
index f6ba15cb5..b436dd21f 100644
--- a/lib/codeclib.h
+++ b/lib/codeclib.h
@@ -28,9 +28,11 @@ typedef struct packet_sequencer_s packet_sequencer_t;
 
 struct codec_def_s {
 	const char *rtpname;
-	int clockrate_mult;
-	int avcodec_id;
+	const int clockrate_mult;
+	const int avcodec_id;
 	const char *avcodec_name;
+	const int default_clockrate;
+	const int default_channels;
 };
 
 struct format_s {
diff --git a/lib/rtplib.c b/lib/rtplib.c
index de05e0ca5..bc5b8d9ab 100644
--- a/lib/rtplib.c
+++ b/lib/rtplib.c
@@ -20,6 +20,7 @@ struct rtp_extension {
 		.encoding		= STR_CONST_INIT(#name),	\
 		.encoding_with_params	= STR_CONST_INIT(#name "/" #c_rate),	\
 		.clock_rate		= c_rate,			\
+		.channels		= 1,				\
 	}
 
 const struct rtp_payload_type rfc_rtp_payload_types[] =
diff --git a/lib/rtplib.h b/lib/rtplib.h
index 17a1c4a7e..17b1541f5 100644
--- a/lib/rtplib.h
+++ b/lib/rtplib.h
@@ -18,12 +18,12 @@ struct rtp_header {
 
 struct rtp_payload_type {
 	int payload_type;
-	str encoding_with_params;
-	str encoding;
-	unsigned int clock_rate;
-	str encoding_parameters;
-	int channels;
-	str format_parameters;
+	str encoding_with_params; // "opus/48000/2"
+	str encoding; // "opus"
+	unsigned int clock_rate; // 48000
+	str encoding_parameters; // "2"
+	int channels; // 2
+	str format_parameters; // value of a=fmtp
 
 	const codec_def_t *codec_def;
 };