diff --git a/daemon/codec.c b/daemon/codec.c
index 25d01b566..d1ad62667 100644
--- a/daemon/codec.c
+++ b/daemon/codec.c
@@ -5,30 +5,42 @@
 #include "log.h"
 #include "rtplib.h"
 #include "codeclib.h"
+#include "ssrc.h"
 
 
 
 
-static codec_handler_func handler_func_stub;
+struct codec_ssrc_handler {
+	struct ssrc_entry h; // must be first
+	mutex_t lock;
+	packet_sequencer_t sequencer;
+	decoder_t *decoder;
+};
+struct transcode_packet {
+	seq_packet_t p; // must be first
+	unsigned long ts;
+	str *payload;
+};
+
+
+static codec_handler_func handler_func_passthrough;
 static codec_handler_func handler_func_transcode;
 
+static struct ssrc_entry *__ssrc_handler_new(void *p);
+static void __ssrc_handler_free(struct codec_ssrc_handler *p);
+
+static void __transcode_packet_free(struct transcode_packet *);
+
 
 static struct codec_handler codec_handler_stub = {
-	.rtp_payload_type = -1,
-	.func = handler_func_stub,
+	.source_pt.payload_type = -1,
+	.func = handler_func_passthrough,
 };
 
 
 
 static void __handler_shutdown(struct codec_handler *handler) {
-	if (handler->decoder)
-		decoder_close(handler->decoder);
-	handler->decoder = NULL;
-}
-
-static void __make_stub(struct codec_handler *handler) {
-	__handler_shutdown(handler);
-	handler->func = handler_func_stub;
+	free_ssrc_hash(&handler->ssrc_hash);
 }
 
 static void __codec_handler_free(void *pp) {
@@ -37,26 +49,38 @@ static void __codec_handler_free(void *pp) {
 	g_slice_free1(sizeof(*h), h);
 }
 
+static struct codec_handler *__handler_new(int pt) {
+	struct codec_handler *handler = g_slice_alloc0(sizeof(*handler));
+	handler->source_pt.payload_type = pt;
+	return handler;
+}
+
+static void __make_passthrough(struct codec_handler *handler) {
+	__handler_shutdown(handler);
+	handler->func = handler_func_passthrough;
+}
+
 static void __make_transcoder(struct codec_handler *handler, struct rtp_payload_type *source,
 		struct rtp_payload_type *dest)
 {
 	assert(source->codec_def != NULL);
 	assert(dest->codec_def != NULL);
+	assert(source->payload_type == handler->source_pt.payload_type);
 
 	__handler_shutdown(handler);
 
+	handler->source_pt = *source;
+	handler->dest_pt = *dest;
 	handler->func = handler_func_transcode;
-	handler->decoder = decoder_new_fmt(source->codec_def, source->clock_rate, 1, 0);
-	if (!handler->decoder)
-		goto err;
+
+	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));
 
 	return;
 
-err:
-	__make_stub(handler);
 }
 
 // call must be locked in W
@@ -93,9 +117,8 @@ void codec_handlers_update(struct call_media *receiver, struct call_media *sink)
 		handler = g_hash_table_lookup(receiver->codec_handlers, &pt->payload_type);
 		if (!handler) {
 			ilog(LOG_DEBUG, "Creating codec handler for " STR_FORMAT, STR_FMT(&pt->encoding));
-			handler = g_slice_alloc0(sizeof(*handler));
-			handler->rtp_payload_type = pt->payload_type;
-			g_hash_table_insert(receiver->codec_handlers, &handler->rtp_payload_type,
+			handler = __handler_new(pt->payload_type);
+			g_hash_table_insert(receiver->codec_handlers, &handler->source_pt.payload_type,
 					handler);
 		}
 
@@ -105,7 +128,7 @@ void codec_handlers_update(struct call_media *receiver, struct call_media *sink)
 		// we default to forwarding without transcoding.
 		if (!pref_dest_codec) {
 			ilog(LOG_DEBUG, "No known/supported sink codec for " STR_FORMAT, STR_FMT(&pt->encoding));
-			__make_stub(handler);
+			__make_passthrough(handler);
 			continue;
 		}
 
@@ -113,7 +136,7 @@ void codec_handlers_update(struct call_media *receiver, struct call_media *sink)
 			// the sink supports this codec. forward without transcoding.
 			// XXX check format parameters as well
 			ilog(LOG_DEBUG, "Sink supports codec " STR_FORMAT, STR_FMT(&pt->encoding));
-			__make_stub(handler);
+			__make_passthrough(handler);
 			continue;
 		}
 
@@ -132,7 +155,7 @@ struct codec_handler *codec_handler_get(struct call_media *m, int payload_type)
 		goto out;
 
 	h = g_atomic_pointer_get(&m->codec_handler_cache);
-	if (G_LIKELY(G_LIKELY(h) && G_LIKELY(h->rtp_payload_type == payload_type)))
+	if (G_LIKELY(G_LIKELY(h) && G_LIKELY(h->source_pt.payload_type == payload_type)))
 		return h;
 
 	h = g_hash_table_lookup(m->codec_handlers, &payload_type);
@@ -154,14 +177,102 @@ void codec_handlers_free(struct call_media *m) {
 }
 
 
-static int handler_func_stub(struct codec_handler *h, struct call_media *media, const str *s, GQueue *out) {
+static int handler_func_passthrough(struct codec_handler *h, struct call_media *media,
+		const struct media_packet *mp, GQueue *out)
+{
 	struct codec_packet *p = g_slice_alloc(sizeof(*p));
-	p->s = *s;
+	p->s = mp->raw;
 	p->free_func = NULL;
 	g_queue_push_tail(out, p);
 	return 0;
 }
-static int handler_func_transcode(struct codec_handler *h, struct call_media *media, const str *s, GQueue *out) {
+
+
+static void __transcode_packet_free(struct transcode_packet *p) {
+	free(p->payload);
+	g_slice_free1(sizeof(*p), p);
+}
+
+static struct ssrc_entry *__ssrc_handler_new(void *p) {
+	struct codec_handler *h = p;
+	struct codec_ssrc_handler *ch = g_slice_alloc0(sizeof(*ch));
+	mutex_init(&ch->lock);
+	packet_sequencer_init(&ch->sequencer, (GDestroyNotify) __transcode_packet_free);
+	ch->decoder = decoder_new_fmt(h->source_pt.codec_def, h->source_pt.clock_rate, 1, 0);
+	if (!ch->decoder)
+		goto err;
+	return &ch->h;
+
+err:
+	__ssrc_handler_free(ch);
+	return NULL;
+}
+static void __ssrc_handler_free(struct codec_ssrc_handler *ch) {
+	packet_sequencer_destroy(&ch->sequencer);
+	if (ch->decoder)
+		decoder_close(ch->decoder);
+	g_slice_free1(sizeof(*ch), ch);
+}
+
+int __packet_decoded(decoder_t *decoder, AVFrame *frame, void *u1, void *u2) {
+	//struct codec_ssrc_handler *ch = u1;
+
+	ilog(LOG_DEBUG, "RTP media successfully decoded");
+
+	av_frame_free(&frame);
+	return 0;
+}
+
+static int handler_func_transcode(struct codec_handler *h, struct call_media *media,
+		const struct media_packet *mp, GQueue *out)
+{
+	if (G_UNLIKELY(!mp->rtp || mp->rtcp))
+		return handler_func_passthrough(h, media, mp, out);
+
+	assert((mp->rtp->m_pt & 0x7f) == h->source_pt.payload_type);
+
+	// create new packet and insert it into sequencer queue
+
+	ilog(LOG_DEBUG, "Received RTP packet: SSRC %u, PT %u, seq %u, TS %u",
+			ntohl(mp->rtp->ssrc), mp->rtp->m_pt, ntohs(mp->rtp->seq_num),
+			ntohl(mp->rtp->timestamp));
+
+	struct codec_ssrc_handler *ch = get_ssrc(mp->rtp->ssrc, h->ssrc_hash);
+	if (G_UNLIKELY(!ch))
+		return 0;
+
+	struct transcode_packet *packet = g_slice_alloc0(sizeof(*packet));
+	packet->p.seq = ntohs(mp->rtp->seq_num);
+	packet->payload = str_dup(&mp->payload);
+	packet->ts = ntohl(mp->rtp->timestamp);
+
+	mutex_lock(&ch->lock);
+
+	if (packet_sequencer_insert(&ch->sequencer, &packet->p)) {
+		// dupe
+		mutex_unlock(&ch->lock);
+		__transcode_packet_free(packet);
+		ilog(LOG_DEBUG, "Ignoring duplicate RTP packet");
+		return 0;
+	}
+
+	// got a new packet, run decoder
+
+	while (1) {
+		packet = packet_sequencer_next_packet(&ch->sequencer);
+		if (G_UNLIKELY(!packet))
+			break;
+
+		ilog(LOG_DEBUG, "Decoding RTP packet: seq %u, TS %lu",
+				packet->p.seq, packet->ts);
+
+		if (decoder_input_data(ch->decoder, packet->payload, packet->ts, __packet_decoded, ch, NULL))
+			ilog(LOG_WARN, "Decoder error while processing RTP packet");
+		__transcode_packet_free(packet);
+	}
+
+	mutex_unlock(&ch->lock);
+
 	return 0;
 }
 
diff --git a/daemon/codec.h b/daemon/codec.h
index d7f18e899..0d52bd048 100644
--- a/daemon/codec.h
+++ b/daemon/codec.h
@@ -5,19 +5,26 @@
 #include <glib.h>
 #include "str.h"
 #include "codeclib.h"
+#include "aux.h"
+#include "rtplib.h"
 
 
 struct call_media;
 struct codec_handler;
+struct media_packet;
+struct ssrc_hash;
 
 
-typedef int codec_handler_func(struct codec_handler *, struct call_media *, const str *, GQueue *);
+typedef int codec_handler_func(struct codec_handler *, struct call_media *, const struct media_packet *,
+		GQueue *);
 
 
 struct codec_handler {
-	int rtp_payload_type;
+	struct rtp_payload_type source_pt; // source_pt.payload_type = hashtable index
+	struct rtp_payload_type dest_pt;
 	codec_handler_func *func;
-	decoder_t *decoder;
+
+	struct ssrc_hash *ssrc_hash;
 };
 
 struct codec_packet {
diff --git a/daemon/media_socket.c b/daemon/media_socket.c
index 3303b4d42..4c23abb76 100644
--- a/daemon/media_socket.c
+++ b/daemon/media_socket.c
@@ -79,6 +79,7 @@ struct packet_handler_ctx {
 	int kernelize; // true if stream can be kernelized
 
 	// output:
+	struct media_packet mp; // passed to handlers
 	GQueue packets_out;
 };
 
@@ -1283,9 +1284,6 @@ static void media_packet_rtcp_demux(struct packet_handler_ctx *phc)
 
 static void media_packet_rtp(struct packet_handler_ctx *phc)
 {
-	struct rtp_header *rtp_h;
-	struct rtcp_packet *rtcp_h;
-
 	phc->payload_type = -1;
 
 	if (G_UNLIKELY(!phc->media->protocol))
@@ -1293,18 +1291,21 @@ static void media_packet_rtp(struct packet_handler_ctx *phc)
 	if (G_UNLIKELY(!phc->media->protocol->rtp))
 		return;
 
-	if (G_LIKELY(!phc->rtcp && !rtp_payload(&rtp_h, NULL, &phc->s))) {
+	if (G_LIKELY(!phc->rtcp && !rtp_payload(&phc->mp.rtp, &phc->mp.payload, &phc->s))) {
+		rtp_padding(phc->mp.rtp, &phc->mp.payload);
+
 		if (G_LIKELY(phc->out_srtp != NULL))
-			__stream_ssrc(phc->in_srtp, phc->out_srtp, rtp_h->ssrc, &phc->ssrc_in,
+			__stream_ssrc(phc->in_srtp, phc->out_srtp, phc->mp.rtp->ssrc, &phc->ssrc_in,
 					&phc->ssrc_out, phc->call->ssrc_hash);
 
 		// check the payload type
 		// XXX redundant between SSRC handling and codec_handler stuff -> combine
-		phc->payload_type = (rtp_h->m_pt & 0x7f);
+		phc->payload_type = (phc->mp.rtp->m_pt & 0x7f);
 		if (G_LIKELY(phc->ssrc_in))
 			phc->ssrc_in->parent->payload_type = phc->payload_type;
 
 		// XXX convert to array? or keep last pointer?
+		// XXX yet another hash table per payload type -> combine
 		struct rtp_stats *rtp_s = g_hash_table_lookup(phc->stream->rtp_stats, &phc->payload_type);
 		if (!rtp_s) {
 			ilog(LOG_WARNING | LOG_FLAG_LIMIT,
@@ -1318,9 +1319,9 @@ static void media_packet_rtp(struct packet_handler_ctx *phc)
 			atomic64_add(&rtp_s->bytes, phc->s.len);
 		}
 	}
-	else if (phc->rtcp && !rtcp_payload(&rtcp_h, NULL, &phc->s)) {
+	else if (phc->rtcp && !rtcp_payload(&phc->mp.rtcp, NULL, &phc->s)) {
 		if (G_LIKELY(phc->out_srtp != NULL))
-			__stream_ssrc(phc->in_srtp, phc->out_srtp, rtcp_h->ssrc, &phc->ssrc_in,
+			__stream_ssrc(phc->in_srtp, phc->out_srtp, phc->mp.rtcp->ssrc, &phc->ssrc_in,
 					&phc->ssrc_out, phc->call->ssrc_hash);
 	}
 }
@@ -1570,7 +1571,7 @@ static int stream_packet(struct packet_handler_ctx *phc) {
 	// this sets rtcp, in_srtp, out_srtp, and sink
 	media_packet_rtcp_demux(phc);
 
-	// this set payload_type, ssrc_in and ssrc_out
+	// this set payload_type, ssrc_in, ssrc_out and mp
 	media_packet_rtp(phc);
 
 
@@ -1595,7 +1596,9 @@ static int stream_packet(struct packet_handler_ctx *phc) {
 	// XXX use a handler for RTCP
 	struct codec_handler *transcoder = codec_handler_get(phc->media, phc->payload_type);
 	// this transfers the packet from 's' to 'packets_out'
-	transcoder->func(transcoder, phc->media, &phc->s, &phc->packets_out);
+	phc->mp.raw = phc->s;
+	if (transcoder->func(transcoder, phc->media, &phc->mp, &phc->packets_out))
+		goto drop;
 
 	if (G_LIKELY(handler_ret >= 0))
 		handler_ret = media_packet_encrypt(phc);
diff --git a/daemon/media_socket.h b/daemon/media_socket.h
index 173f8e9f6..3d25eeba8 100644
--- a/daemon/media_socket.h
+++ b/daemon/media_socket.h
@@ -68,6 +68,12 @@ struct stream_fd {
 	struct crypto_context		crypto;		/* IN direction, LOCK: stream->in_lock */
 	struct dtls_connection		dtls;		/* LOCK: stream->in_lock */
 };
+struct media_packet {
+	str raw;
+	struct rtp_header *rtp;
+	struct rtcp_packet *rtcp;
+	str payload;
+};
 
 
 
diff --git a/perl/NGCP/Rtpclient/RTP.pm b/perl/NGCP/Rtpclient/RTP.pm
index 7d667724b..7889b8194 100644
--- a/perl/NGCP/Rtpclient/RTP.pm
+++ b/perl/NGCP/Rtpclient/RTP.pm
@@ -25,6 +25,7 @@ sub new {
 	$self->{octet_count} = 0;
 	$self->{other_ssrcs} = {};
 	$self->{args} = \%args;
+	$self->{payload_type} = $args{payload_type} // 0;
 
 	return $self;
 }
@@ -34,7 +35,8 @@ sub timer {
 
 	time() < $self->{next_send} and return;
 
-	my $hdr = pack("CCnNN", 0x80, 0x00, $self->{seq}, $self->{timestamp}->bstr(), $self->{ssrc});
+	my $hdr = pack("CCnNN", 0x80, $self->{payload_type}, $self->{seq}, $self->{timestamp}->bstr(),
+		$self->{ssrc});
 	my $payload = chr(rand(256)) x $self->{payload}; # XXX adapt to codec
 
 	my $lost = 0;
diff --git a/perl/NGCP/Rtpclient/SDP.pm b/perl/NGCP/Rtpclient/SDP.pm
index e9b19253f..fa50e8384 100644
--- a/perl/NGCP/Rtpclient/SDP.pm
+++ b/perl/NGCP/Rtpclient/SDP.pm
@@ -123,17 +123,29 @@ use Socket;
 use Socket6;
 use IO::Socket;
 
+my %codec_map = (
+	PCMA => { payload_type => 8 },
+	PCMU => { payload_type => 0 },
+);
+my %payload_type_map = map {$codec_map{$_}{payload_type} => $_} keys(%codec_map);
+
+sub _codec_list_to_hash {
+	my ($list) = @_;
+	return { map { $_ => { %{$codec_map{$_}} } } @{$list} };
+}
+
 sub new {
-	my ($class, $rtp, $rtcp, $protocol, $type) = @_;
+	my ($class, $rtp, $rtcp, %args) = @_;
 
 	my $self = {};
 	bless $self, $class;
 
 	$self->{rtp} = $rtp; # main transport
 	$self->{rtcp} = $rtcp; # optional
-	$self->{protocol} = $protocol // 'RTP/AVP';
-	$self->{type} = $type // 'audio';
-	$self->{payload_types} = [0];
+	$self->{protocol} = $args{protocol} // 'RTP/AVP';
+	$self->{type} = $args{type} // 'audio';
+	$self->{codec_list} = $args{codecs};
+	$self->{codecs} = _codec_list_to_hash(@{$self->{codecs}});
 
 	$self->{additional_attributes} = [];
 
@@ -149,7 +161,9 @@ sub new_remote {
 	$self->{protocol} = $protocol;
 	$self->{port} = $port;
 	$self->{type} = $type;
-	$self->{payload_types} = [split(/ /, $payload_types)];
+	my @payload_types = [split(/ /, $payload_types)];
+	$self->{codec_list} = [ map {$payload_type_map{$_}} @payload_types ];
+	$self->{codecs} = _codec_list_to_hash(@{$self->{codecs}});
 
 	return $self;
 };
@@ -165,8 +179,10 @@ sub encode {
 	my $pconn = $parent_connection ? NGCP::Rtpclient::SDP::encode_address($parent_connection) : '';
 	my @out;
 
+	my @payload_types = map {$codec_map{$_}{payload_type}} @{$self->{codec_list}};
+
 	push(@out, "m=$self->{type} " . $self->{rtp}->sockport() . ' ' . $self->{protocol} . ' '
-		. join(' ', @{$self->{payload_types}}));
+		. join(' ', @payload_types));
 
 	my $rtpconn = NGCP::Rtpclient::SDP::encode_address($self->{rtp});
 	$rtpconn eq $pconn or push(@out, "c=$rtpconn");
diff --git a/perl/NGCP/Rtpengine/Test.pm b/perl/NGCP/Rtpengine/Test.pm
index 4a572abef..a059baf50 100644
--- a/perl/NGCP/Rtpengine/Test.pm
+++ b/perl/NGCP/Rtpengine/Test.pm
@@ -138,6 +138,7 @@ sub _new {
 
 	$self->{parent} = $parent;
 	$self->{tag} = rand();
+	$self->{codecs} = $args{codecs} // [qw(PCMU)];
 
 	# create media sockets
 	my @addresses = @{$parent->{all_addresses}};
@@ -181,7 +182,10 @@ sub _new {
 	$args{protocol} and $proto = $args{protocol};
 
 	$self->{local_media} = $self->{local_sdp}->add_media(NGCP::Rtpclient::SDP::Media->new(
-		$self->{main_sockets}->[0], $self->{main_sockets}->[1], $proto)); # main rtp and rtcp
+		$self->{main_sockets}->[0], $self->{main_sockets}->[1], # main rtp and rtcp
+		protocol => $proto,
+		codecs => $self->{codecs},
+	));
 	# XXX support multiple medias
 
 	if ($args{dtls}) {
@@ -273,7 +277,7 @@ sub _default_req_args {
 
 	my $req = { command => $cmd, 'call-id' => $self->{parent}->{callid} };
 
-	for my $cp (qw(sdp from-tag to-tag ICE transport-protocol address-family label direction)) {
+	for my $cp (qw(sdp from-tag to-tag ICE transport-protocol address-family label direction codec)) {
 		$args{$cp} and $req->{$cp} = $args{$cp};
 	}
 	for my $cp (@{$args{flags}}) {
diff --git a/t/test-transcode.pl b/t/test-transcode.pl
new file mode 100755
index 000000000..2f413903f
--- /dev/null
+++ b/t/test-transcode.pl
@@ -0,0 +1,27 @@
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+use NGCP::Rtpengine::Test;
+use IO::Socket;
+
+my $r = NGCP::Rtpengine::Test->new();
+my ($a, $b) = $r->client_pair(
+	{sockdomain => &Socket::AF_INET, codecs => [qw(PCMA)]},
+	{sockdomain => &Socket::AF_INET, codecs => [qw(PCMU)]}
+);
+
+$r->timer_once(3, sub {
+		$b->answer($a, ICE => 'remove', label => "callee");
+		$a->start_rtp();
+		$a->start_rtcp();
+	});
+$r->timer_once(10, sub { $r->stop(); });
+
+$a->offer($b, ICE => 'remove', label => "caller", codec => { transcode => ['PCMU']});
+$b->start_rtp();
+$b->start_rtcp();
+
+$r->run();
+
+$a->teardown(dump => 1);