mgcp/rtp: Fix timestamp offset when patching RTP packets
The current implementation increments the seqno but does not increment
the RTP timestamp, leading to two identical timestamps following one
after the other.
This patch fixes this by adding the computed tsdelta when the offset
is calulated. In the unlikely case, that a tsdelta hasn't been
computed yet when the SSRC changes, a tsdelta is computed based on
the RTP rate and a RTP packet duration of 20ms (one speech frame per
channel and packet). If the RTP rate is not known, a rate of 8000 is
assumed.
Note that this approach presumes, that the per RTP packet duration
(in samples) is the same for the last two packets of the stream being
replaced (the first one).
Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/libmgcp/mgcp_network.c b/openbsc/src/libmgcp/mgcp_network.c
index 72d0a5c..75d39c1 100644
--- a/openbsc/src/libmgcp/mgcp_network.c
+++ b/openbsc/src/libmgcp/mgcp_network.c
@@ -238,15 +238,30 @@
state->transit = arrival_time - timestamp;
state->out_stream = state->in_stream;
} else if (state->in_stream.ssrc != rtp_hdr->ssrc) {
+ int32_t tsdelta = state->out_stream.last_tsdelta;
+ if (tsdelta == 0) {
+ tsdelta = rtp_end->rate * rtp_end->frames_per_packet *
+ rtp_end->frame_duration_num /
+ rtp_end->frame_duration_den;
+ LOGP(DMGCP, LOGL_NOTICE,
+ "Computed timestamp delta %d based on "
+ "rate %d, num frames %d, frame duration %d/%d\n",
+ tsdelta, rtp_end->rate, rtp_end->frames_per_packet,
+ rtp_end->frame_duration_num,
+ rtp_end->frame_duration_den);
+ }
state->in_stream.ssrc = rtp_hdr->ssrc;
state->seq_offset = (state->out_stream.last_seq + 1) - seq;
- state->timestamp_offset = state->out_stream.last_timestamp - timestamp;
+ state->timestamp_offset =
+ (state->out_stream.last_timestamp + tsdelta) - timestamp;
state->patch = endp->allow_patch;
LOGP(DMGCP, LOGL_NOTICE,
- "The SSRC changed on 0x%x SSRC: %u offset: %d from %s:%d in %d\n",
+ "The SSRC changed on 0x%x SSRC: %u offset: %d tsdelta: %d "
+ "from %s:%d in %d\n",
ENDPOINT_NUMBER(endp), state->in_stream.ssrc,
- state->seq_offset, inet_ntoa(addr->sin_addr),
- ntohs(addr->sin_port), endp->conn_mode);
+ state->seq_offset, tsdelta,
+ inet_ntoa(addr->sin_addr), ntohs(addr->sin_port),
+ endp->conn_mode);
state->in_stream.last_tsdelta = 0;
} else {