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A stream the audio player consumes keeps the sender's sequence numbers #2209

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d7eacbf
MT#55283 SSRC substitution re-encrypts, and each sink gets its own copy
Oct 21, 2026
f06bb78
MT#55283 a stream the audio player consumes keeps the sender's numbers
Oct 21, 2026
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10 changes: 7 additions & 3 deletions daemon/codec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -233,6 +233,7 @@ struct codec_ssrc_handler {
uint64_t skip_pts;

bool rtp_mark;
bool decode_only; // consumes without replacing: doesn't move the seq offset
};
struct transcode_packet {
seq_packet_t p; // must be first
Expand Down Expand Up @@ -2429,7 +2430,8 @@ static int __handler_func_sequencer(struct media_packet *mp, struct transcode_pa

if (seq_ret == 1) {
// seq reset - update output seq. we keep our output seq clean
ssrc_out->seq_diff -= packet->p.seq - seq_ori;
if (!ch->decode_only)
ssrc_out->seq_diff -= packet->p.seq - seq_ori;
seq_ret = 0;
}

Expand Down Expand Up @@ -4029,7 +4031,7 @@ static void __dtx_send_later(struct codec_timer *ct) {
// release and try again
mutex_unlock(&dtxb->lock);

if (call && mp_copy.ssrc_out) {
if (call && mp_copy.ssrc_out && !ch->decode_only) {
// packet consumed - track seq
rwlock_lock_r(&call->master_lock);
__ssrc_lock_both(&mp_copy);
Expand Down Expand Up @@ -4542,6 +4544,7 @@ static struct ssrc_entry *__ssrc_handler_decode_new(void *p) {

__auto_type ch = obj_alloc0(struct codec_ssrc_handler, __free_ssrc_handler);
ch->handler = h;
ch->decode_only = true;
ch->ptime = h->dest_pt.ptime;

format_t dest_format = {
Expand Down Expand Up @@ -4897,7 +4900,8 @@ static tc_code __rtp_decode_direct(struct codec_ssrc_handler *ch, struct codec_s
code = ret == 0 ? TCC_OK : TCC_ERR;
}
}
__buffer_delay_seq(input_ch->handler->delay_buffer, mp, -1);
if (!ch->decode_only) // consumed, not replaced: doesn't count towards the seq offset
__buffer_delay_seq(input_ch->handler->delay_buffer, mp, -1);
return code;
}
static tc_code __rtp_decode_async(struct codec_ssrc_handler *ch, struct codec_ssrc_handler *input_ch,
Expand Down
52 changes: 38 additions & 14 deletions daemon/media_socket.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1790,6 +1790,11 @@ static const char *kernelize_target(kernelize_state *s, struct packet_stream *st
return NULL;
}

// the kernel's ssrc_subst cases: echo, transcoding or a fixed egress SSRC
static bool sink_substitutes_ssrc(struct call_media *in, const struct sink_handler *sh, struct call_media *out) {
return MEDIA_ISSET(in, ECHO) || sh->attrs.transcoding || (out && out->fixed_egress_ssrc);
}

/**
* The linkage between userspace and kernel module is in the kernelize_one().
*
Expand Down Expand Up @@ -1889,8 +1894,7 @@ static const char *kernelize_one(kernelize_state *s,

}

if (MEDIA_ISSET(media, ECHO) || sink_handler->attrs.transcoding
|| sink->media->fixed_egress_ssrc)
if (sink_substitutes_ssrc(media, sink_handler, sink->media))
redi->output.ssrc_subst = 1;

__re_address_translate_ep(&redi->output.dst_addr, &sink->endpoint);
Expand Down Expand Up @@ -2623,7 +2627,7 @@ const struct streamhandler *determine_sink_handler(struct packet_stream *in, str
must_recrypt = true;
else if (ML_ISSET(in->media->monologue, INJECT_DTMF) || (out && ML_ISSET(out->media->monologue, INJECT_DTMF)))
must_recrypt = true;
else if (sh->attrs.transcoding)
else if (sink_substitutes_ssrc(media_in, sh, media_out)) // the header is rewritten: the packet is encrypted anew
must_recrypt = true;
else if (in->call->recording)
must_recrypt = true;
Expand Down Expand Up @@ -3487,6 +3491,22 @@ void media_packet_release(struct media_packet *mp) {
}


// gives a sink its own copy of the packet to rewrite, with the header, payload and extensions pointing into it
static void media_packet_sink_copy(struct media_packet *mp, GQueue *free_list) {
char *buf = bufferpool_alloc(media_bufferpool, mp->raw.len + RTP_BUFFER_TAIL_ROOM);
memcpy(buf, mp->raw.s, mp->raw.len);
g_queue_push_tail(free_list, buf);
if (mp->rtp)
mp->rtp = (void *) (buf + ((char *) mp->rtp - mp->raw.s));
if (mp->rtcp)
mp->rtcp = (void *) (buf + ((char *) mp->rtcp - mp->raw.s));
if (mp->payload.s)
mp->payload.s = buf + (mp->payload.s - mp->raw.s);
if (mp->extensions.s)
mp->extensions.s = buf + (mp->extensions.s - mp->raw.s);
mp->raw.s = buf;
}

static int media_packet_queue_dup(codec_packet_q *q) {
IQUEUE_FOREACH(q, p) {
if (p->free_func) // nothing to do, already private
Expand Down Expand Up @@ -3661,12 +3681,26 @@ static int stream_packet(struct packet_handler_ctx *phc) {

///////////////// EGRESS HANDLING

str orig_raw = STR_NULL;
// the handlers may rewrite the packet in place, but we may have multiple outputs: every sink
// starts from the packet as received and gets its own copy of it unless it's the last one
const str orig_raw = phc->mp.raw;
struct rtp_header *const orig_rtp = phc->mp.rtp;
struct rtcp_packet *const orig_rtcp = phc->mp.rtcp;
const str orig_payload = phc->mp.payload;
const str orig_extensions = phc->mp.extensions;

for (__auto_type sh_link = phc->sinks->head; sh_link; sh_link = sh_link->next) {
struct sink_handler *sh = sh_link->data;
struct packet_stream *sink = sh->bundle_sink;

phc->mp.raw = orig_raw;
phc->mp.rtp = orig_rtp;
phc->mp.rtcp = orig_rtcp;
phc->mp.payload = orig_payload;
phc->mp.extensions = orig_extensions;
if (sh_link->next)
media_packet_sink_copy(&phc->mp, &free_list);

// this sets rtcp, in_srtp, out_srtp, media_out, and sink
media_packet_rtcp_mux(phc, sh);

Expand All @@ -3678,16 +3712,6 @@ static int stream_packet(struct packet_handler_ctx *phc) {
if (phc->rtcp) {
phc->rtcp_discard = false;
handler_ret = -1;
// these functions may do in-place rewriting, but we may have multiple
// outputs - make a copy if this isn't the last sink
if (sh_link->next) {
if (!orig_raw.s)
orig_raw = phc->mp.raw;
char *buf = bufferpool_alloc(media_bufferpool, orig_raw.len + RTP_BUFFER_TAIL_ROOM);
memcpy(buf, orig_raw.s, orig_raw.len);
phc->mp.raw.s = buf;
g_queue_push_tail(&free_list, buf);
}
if (do_rtcp_parse(phc))
goto out;
if (phc->rtcp_discard)
Expand Down
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