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fix: RTP timestamp regression after DTX transcoder restarts #2191

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fix: RTP timestamp regression after DTX transcoder restarts #2191

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2578d33
Fix RTP output clock continuity across DTX restarts
vingarzan Oct 3, 2026
54616c4
fix timestamp regression by restricting output clock caching to DTX p…
vingarzan Oct 9, 2026
20cf982
Merge branch 'master' into fix/dtx-output-clock-continuity
vingarzan Oct 9, 2026
8fb7c5f
test: update reverse AMR-WB codec-change test to verify elapsed outpu…
vingarzan Oct 9, 2026
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21 changes: 18 additions & 3 deletions daemon/codec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4061,6 +4061,8 @@ static void __dtx_send_later(struct codec_timer *ct) {
rwlock_lock_r(&call->master_lock);
__ssrc_lock_both(&mp_copy);

mp_copy.dtx = true;

if (dtxp) {
ilogs(dtx, LOG_DEBUG, "Decoding DTX-buffered RTP packet (TS %lu) now; "
"%i packets left in queue", ts, p_left);
Expand Down Expand Up @@ -4100,8 +4102,6 @@ static void __dtx_send_later(struct codec_timer *ct) {
mutex_unlock(&dtxb->lock);
}
}
if (ch && ch->encoder && mp_copy.ssrc_out)
mp_copy.ssrc_out->ts_out = ch->encoder->next_pts + ch->csch.first_ts;

mutex_lock(&dtxb->lock);

Expand Down Expand Up @@ -4726,6 +4726,15 @@ static void packet_encoded_tx(struct codec_ssrc_handler *ch, struct media_packet
if (!repeats)
break;
} while (repeats--);

// Save the clock of the actual output encoder for DTX restarts. The DTX decoder
// may run at a different rate and cannot supply the timestamp for this listener.
// Ordinary transcoding must retain the input timestamp origin when reconfigured.
if (mp->dtx && !is_dtmf) {
mp->ssrc_out->ts_out = ch->csch.first_ts + fraction_divl(pts + duration, cr_fact);
mp->ssrc_out->ts_out_time = rtpe_now
+ fraction_divl(duration, cr_fact) * 1000000LL / ch->handler->dest_pt.clock_rate;
}
}


Expand Down Expand Up @@ -4923,8 +4932,14 @@ static tc_code packet_decode(struct codec_ssrc_handler *ch, struct codec_ssrc_ha
{
tc_code ret = TCC_OK;

if (!ch->csch.first_ts)
if (!ch->csch.first_ts) {
ch->csch.first_ts = mp->ssrc_out->ts_out ?: packet->ts;
// A stopped encoder does not produce samples while prompts or floor
// blocking are active. Keep that elapsed time in the listener's RTP clock.
if (mp->ssrc_out->ts_out_time && rtpe_now > mp->ssrc_out->ts_out_time)
ch->csch.first_ts += (rtpe_now - mp->ssrc_out->ts_out_time)
* ch->handler->dest_pt.clock_rate / 1000000;
}

if (ch->decoder && ch->decoder->def->dtmf) {
if (packet_dtmf_event(ch, input_ch, packet, mp) == -1)
Expand Down
1 change: 1 addition & 0 deletions include/media_socket.h
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Original file line number Diff line number Diff line change
Expand Up @@ -313,6 +313,7 @@ struct media_packet {
struct sink_handler sink;
struct media_player_cache_entry *cache_entry;
bool recording_egress;
bool dtx; // processed by the DTX timer; retain the output encoder clock

struct rtp_header *rtp;
struct rtcp_packet *rtcp;
Expand Down
1 change: 1 addition & 0 deletions include/ssrc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,7 @@ struct ssrc_entry_call {
uint32_t ssrc_map_out;
uint16_t seq_out;
unsigned long ts_out;
int64_t ts_out_time; // wall clock corresponding to the next output RTP timestamp
bool seq_set;

// RTCP stats
Expand Down
7 changes: 5 additions & 2 deletions t/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -90,7 +90,7 @@ include ../lib/common.Makefile
daemon-tests-bundle daemon-tests-dtls daemon-tests-rollback \
daemon-tests-rollback-redis daemon-tests-redis-srtp-index \
daemon-tests-recording daemon-tests-create daemon-tests-created-subscriptions daemon-tests-alias \
daemon-tests-kernel-api \
daemon-tests-kernel-api daemon-tests-dtx-clock \
daemon-tests-video daemon-tests-inject daemon-tests-dtx-dtmf

TESTS := test-bitstr aes-crypt aead-aes-crypt test-const_str_hash.strhash
Expand Down Expand Up @@ -143,7 +143,7 @@ daemon-tests: daemon-tests-main daemon-tests-jb daemon-tests-pubsub daemon-tests
daemon-tests-bundle daemon-tests-dtls daemon-tests-rollback daemon-tests-rollback-redis \
daemon-tests-redis-srtp-index \
daemon-tests-recording daemon-tests-create daemon-tests-created-subscriptions \
daemon-tests-dtx daemon-tests-dtx-cn daemon-tests-dtx-no-shift daemon-tests-dtx-dtmf \
daemon-tests-dtx daemon-tests-dtx-cn daemon-tests-dtx-no-shift daemon-tests-dtx-dtmf daemon-tests-dtx-clock \
daemon-tests-alias \
daemon-tests-kernel-api \
daemon-tests-video daemon-tests-inject
Expand Down Expand Up @@ -184,6 +184,9 @@ daemon-tests-dtx: daemon-test-deps
daemon-tests-dtx-dtmf: daemon-test-deps
./auto-test-helper "$@" perl -I../perl auto-daemon-tests-dtx-dtmf.pl

daemon-tests-dtx-clock: daemon-test-deps
./auto-test-helper "$@" perl -I../perl auto-daemon-tests-dtx-clock.pl

daemon-tests-dtx-no-shift: daemon-test-deps
./auto-test-helper "$@" perl -I../perl auto-daemon-tests-dtx-no-shift.pl

Expand Down
129 changes: 129 additions & 0 deletions t/auto-daemon-tests-dtx-clock.pl
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Original file line number Diff line number Diff line change
@@ -0,0 +1,129 @@
#!/usr/bin/perl

use strict;
use warnings;
use NGCP::Rtpengine::Test;
use NGCP::Rtpclient::SRTP;
use NGCP::Rtpengine::AutoTest;
use Test::More;

# Repeated floor bursts must retain each output encoder clock through prompt playback.
autotest_start(qw(--config-file=none -t -1 -i 203.0.113.1
-n 2223 -f -L 7 -E --silence-detect=1 --dtx-delay=50 --max-dtx=1)) or die;

use Time::HiRes qw(time sleep);
use IO::Select;

# Exercise equal rates, different RTP rates, and the G.722 sample/RTP rate factor.
for my $profile (
['PCMA/8000', 8, 8000, 100000],
['opus/48000/2', 96, 48000, 100000],
['G722/8000', 9, 8000, 0xfffff000],
) {
my ($codec, $pt, $rate, $origin) = @$profile;
my $offer_pts = $pt == 96 ? '96 97' : $pt;
my $offer_attrs = "a=rtpmap:$pt $codec";
if ($pt == 96) {
$offer_attrs .= "\na=fmtp:96 useinbandfec=1\na=rtpmap:97 telephone-event/48000\na=fmtp:97 0-15";
}
my ($sock_a, $sock_b) = new_call([qw(198.51.100.10 5000)], [qw(198.51.100.10 5002)]);
my $name = "DTX output clock across playback: $codec";

my ($port_a) = offer($name, { codec => { transcode => [$codec] } }, <<SDP);
v=0
o=- 1545997027 1 IN IP4 198.51.100.10
s=tester
t=0 0
m=audio 5000 RTP/AVP 0 101
c=IN IP4 198.51.100.10
a=rtpmap:101 telephone-event/8000
a=sendrecv
----------------------------------
v=0
o=- 1545997027 1 IN IP4 198.51.100.10
s=tester
t=0 0
m=audio PORT RTP/AVP 0 $offer_pts 101
c=IN IP4 203.0.113.1
a=rtpmap:0 PCMU/8000
$offer_attrs
a=rtpmap:101 telephone-event/8000
a=sendrecv
a=rtcp:PORT
SDP

my ($port_b) = answer($name, {}, <<SDP);
v=0
o=- 1545997027 1 IN IP4 198.51.100.10
s=tester
t=0 0
m=audio 5002 RTP/AVP $pt 101
a=rtpmap:$pt $codec
c=IN IP4 198.51.100.10
a=rtpmap:101 telephone-event/8000
a=sendrecv
----------------------------------
v=0
o=- 1545997027 1 IN IP4 198.51.100.10
s=tester
t=0 0
m=audio PORT RTP/AVP 0 101
c=IN IP4 203.0.113.1
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=sendrecv
a=rtcp:PORT
SDP


# A short prompt on its own SSRC interrupts the transcoder between bursts.
my $pcm = "\0" x 1600;
my $wav = pack('a4Va4a4VvvVVvva4V', 'RIFF', 36 + length($pcm), 'WAVE',
'fmt ', 16, 1, 1, 8000, 16000, 2, 16, 'data', length($pcm)) . $pcm;
my ($seq, $last_ts, $last_time, $audio_ssrc) = (100, undef, undef, undef);
for my $burst (0..2) {
for my $i (0..9) {
snd($sock_a, $port_b, rtp(0, $seq++, $origin + $burst * 16000 + $i * 160,
0x5678, "\x40" x 160));
sleep(0.02);
}
my $sel = IO::Select->new($sock_b);
my $end = time() + 0.3;
my $received = 0;
while (time() < $end && $sel->can_read(0.1)) {
my $p;
$sock_b->recv($p, 65535);
my ($out_pt, $q, $ts, $ssrc) = unpack('x C n N N', $p);
is($out_pt & 0x7f, $pt, 'burst uses the negotiated output codec');
$audio_ssrc //= $ssrc;
is($ssrc, $audio_ssrc, 'speech SSRC survives playback transitions');
my $now = time();
if (defined $last_ts) {
my $delta = ($ts - $last_ts) & 0xffffffff;
cmp_ok($delta, '<', 0x80000000, 'output clock does not rewind');
if ($now - $last_time > 1) {
# Receive after sending a 200 ms batch; allow that batching skew.
cmp_ok(abs($delta / $rate - ($now - $last_time)), '<', 0.3,
'RTP clock includes elapsed playback and silence');
}
}
$last_ts = $ts;
$last_time = $now;
$received++;
}
cmp_ok($received, '>=', 10, 'each burst produces output promptly');
rtpe_req('block media', $name, {'from-tag' => ft(), flags => ['directional']});
rtpe_req('play media', $name, {'from-tag' => tt(), blob => $wav});
sleep(0.2);
rtpe_req('stop media', $name, {'from-tag' => tt()});
while ($sel->can_read(0.01)) {
my $p;
$sock_b->recv($p, 65535);
}
sleep(1.4);
rtpe_req('unblock media', $name, {'from-tag' => ft(), flags => ['directional']});
}
rtpe_req('delete', $name, {'from-tag' => ft()});
}

done_testing();
35 changes: 26 additions & 9 deletions t/auto-daemon-tests-dtx.pl
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@
my ($sock_a, $sock_b, $sock_c, $sock_d, $port_a, $port_b, $ssrc, $ssrc_b, $resp,
$sock_ax, $sock_bx, $port_ax, $port_bx,
$srtp_ctx_a, $srtp_ctx_b, $srtp_ctx_a_rev, $srtp_ctx_b_rev,
@ret1, @ret2, @ret3, @ret4, $srtp_key_a, $srtp_key_b, $ts, $seq);
@ret1, @ret2, @ret3, @ret4, $srtp_key_a, $srtp_key_b, $ts, $seq, $resume_time);



Expand Down Expand Up @@ -705,10 +705,13 @@
rcv($sock_b, $port_a, rtpm(96, $seq + 10, 7200, 0x5678, "\xf0\x1c\x50\x54\x30\x77\xf3\xdd\x1d\xd3\x57\x6b\xce\xc7\xcd\x7a\x17\x71\x05\x36\x04\x42\x70\x72\x73\x25\x0c\x14\x26\x2a\x05\x72\x03\x90\xf2\x5c\x48\xd8"));

# inject old PCM
$resume_time = Time::HiRes::time();
snd($sock_a, $port_b, rtp(0, 2004, 5120, 0x5678, "\x40" x 160));
snd($sock_a, $port_b, rtp(0, 2006, 5440, 0x5678, "\x40" x 160));
# packet dropped
rcv_no($sock_b);
# Make the elapsed gap large enough to distinguish it from a single 20 ms increment.
Time::HiRes::usleep(200000);

# reinvite back to PCMU

Expand Down Expand Up @@ -762,9 +765,12 @@


snd($sock_a, $port_b, rtp(0, 2007, 5760, 0x5678, "\x40" x 160));
rcv($sock_b, $port_a, rtpm(96, $seq + 11, 7520, $ssrc, "\xf0\x1c\x21\x40\x00\xff\xfb\xfc\x92\x17\x2f\x21\x34\xcb\x60\x28\x1b\x23\x23\x30\x04\x87\xb1\x30\x4f\x91\x04\x5e\xd9\xc6\x6c\xfc\x28\xed\xe1\xc6\xd5\xe0"));
# AMR-WB uses a 16 kHz output clock, independently of the G.711 input origin.
($ts) = rcv($sock_b, $port_a, rtpm(96, $seq + 11, -1, $ssrc, "\xf0\x1c\x21\x40\x00\xff\xfb\xfc\x92\x17\x2f\x21\x34\xcb\x60\x28\x1b\x23\x23\x30\x04\x87\xb1\x30\x4f\x91\x04\x5e\xd9\xc6\x6c\xfc\x28\xed\xe1\xc6\xd5\xe0"));
cmp_ok(abs(($ts - 7200) / 16000 - (Time::HiRes::time() - $resume_time)), '<', 0.1,
'AMR-WB output clock advances through codec reconfiguration');
snd($sock_a, $port_b, rtp(0, 2007, 5920, 0x5678, "\x40" x 160));
rcv($sock_b, $port_a, rtpm(96, $seq + 12, 7840, $ssrc, "\xf0\x1c\xc8\xc6\x04\x55\x92\x65\x07\x9c\x21\x19\x06\x71\x89\xd4\x66\xe6\x84\xe6\xc5\xc4\xc4\xcc\x5e\xc1\xc5\xf5\x4c\x55\xde\x71\x9a\x57\xc0\xde\xe4\xd0"));
rcv($sock_b, $port_a, rtpm(96, $seq + 12, $ts + 320, $ssrc, "\xf0\x1c\xc8\xc6\x04\x55\x92\x65\x07\x9c\x21\x19\x06\x71\x89\xd4\x66\xe6\x84\xe6\xc5\xc4\xc4\xcc\x5e\xc1\xc5\xf5\x4c\x55\xde\x71\x9a\x57\xc0\xde\xe4\xd0"));

rtpe_req('delete', 'G.711/AMR-WB codec change reverse', { 'from-tag' => ft() });

Expand Down Expand Up @@ -894,6 +900,7 @@
rcv($sock_b, $port_a, rtpm(8, $seq + 10, 5600, 0x5678, "\xd5\xd5\xd5\xd5\x55\x55\xd5\x55\x55\xd5\x55\x55\x55\x55\xd5\x55\x55\xd5\x55\xd5\x55\xd5\x55\x55\xd5\xd5\xd5\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\xd5\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\xd5\x55\x55\xd5\x55\x55\x55\x55\x55\x55\x55\xd5\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\xd5\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\xd5\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\xd5\xd5\xd5\xd5\xd5\xd5\xd5\x55\x55\x55\x55\x55\x55\x55"));

# inject old PCM
$resume_time = Time::HiRes::time();
snd($sock_a, $port_b, rtp(0, 2006, 5760, 0x5678, "\x40" x 160));
# packet dropped
rcv_no($sock_b);
Expand Down Expand Up @@ -947,9 +954,12 @@


snd($sock_a, $port_b, rtp(0, 2007, 5920, 0x5678, "\x40" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 11, 5760, $ssrc, "\x68" x 160));
# Reconfiguration retains elapsed time in the output clock, independently of the input origin.
($ts) = rcv($sock_b, $port_a, rtpm(8, $seq + 11, -1, $ssrc, "\x68" x 160));
cmp_ok(abs(($ts - 5600) / 8000 - (Time::HiRes::time() - $resume_time)), '<', 0.1,
'output clock advances through codec reconfiguration');
snd($sock_a, $port_b, rtp(0, 2008, 6080, 0x5678, "\x40" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 12, 5920, $ssrc, "\x68" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 12, $ts + 160, $ssrc, "\x68" x 160));

rtpe_req('delete', 'G.711/AMR-WB codec change with timing', { 'from-tag' => ft() });

Expand Down Expand Up @@ -1081,6 +1091,7 @@
rcv($sock_b, $port_a, rtpm(8, $seq + 10, 5600, 0x5678, "\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5\xd5"));

# inject old PCM
$resume_time = Time::HiRes::time();
snd($sock_a, $port_b, rtp(0, 2006, 5600, 0x5678, "\x40" x 160));
# packet dropped
rcv_no($sock_b);
Expand Down Expand Up @@ -1134,7 +1145,10 @@


snd($sock_a, $port_b, rtp(0, 2007, 5760, 0x5678, "\x40" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 11, 5760, $ssrc, "\x68" x 160));
# Reconfiguration retains elapsed time in the output clock, independently of the input origin.
($ts) = rcv($sock_b, $port_a, rtpm(8, $seq + 11, -1, $ssrc, "\x68" x 160));
cmp_ok(abs(($ts - 5600) / 8000 - (Time::HiRes::time() - $resume_time)), '<', 0.1,
'output clock advances through codec reconfiguration');

rtpe_req('delete', 'G.711/AMR codec change with timing', { 'from-tag' => ft() });

Expand Down Expand Up @@ -2044,14 +2058,17 @@
rcv($sock_b, $port_a, rtpm(8, $seq + 9 + $i, 5440 + $i * 160, $ssrc, "\xd5" x 160));
}
# now shut down
$resume_time = Time::HiRes::time();
rcv_no($sock_b);
# start audio again
snd($sock_a, $port_b, rtp(0, 2005, 90000, 0x5678, "\x40" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 507, 90000, $ssrc, "\x68" x 160));
($ts) = rcv($sock_b, $port_a, rtpm(8, $seq + 507, -1, $ssrc, "\x68" x 160));
cmp_ok(abs(($ts - (5440 + 497 * 160)) / 8000 - (Time::HiRes::time() - $resume_time)), '<', 0.1,
'output clock survives maximum DTX shutdown');
snd($sock_a, $port_b, rtp(0, 2006, 90160, 0x5678, "\x40" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 508, 90160, $ssrc, "\x68" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 508, $ts + 160, $ssrc, "\x68" x 160));
# DTX -> silence
rcv($sock_b, $port_a, rtpm(8, $seq + 509, 90320, $ssrc, "\xd5" x 160));
rcv($sock_b, $port_a, rtpm(8, $seq + 509, $ts + 320, $ssrc, "\xd5" x 160));

rtpe_req('delete', 'G.711 DTX ptime change', { 'from-tag' => ft() });

Expand Down
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