mgcp: Allow switching the audio streams, patch the header
Patch the sequence number, the SSRC and the timestamp to
allow to mix various voice streams, e.g. toggling the loop
during the call.
diff --git a/openbsc/src/mgcp/mgcp_network.c b/openbsc/src/mgcp/mgcp_network.c
index d2dbeeb..b5e2cdd 100644
--- a/openbsc/src/mgcp/mgcp_network.c
+++ b/openbsc/src/mgcp/mgcp_network.c
@@ -97,6 +97,7 @@
static void patch_and_count(struct mgcp_rtp_state *state, int payload, char *data, int len)
{
uint16_t seq;
+ uint32_t timestamp;
struct rtp_hdr *rtp_hdr;
if (len < sizeof(*rtp_hdr))
@@ -104,15 +105,36 @@
rtp_hdr = (struct rtp_hdr *) data;
seq = ntohs(rtp_hdr->sequence);
+ timestamp = ntohl(rtp_hdr->timestamp);
if (!state->initialized) {
- state->seq_no = seq;
+ state->seq_no = seq - 1;
+ state->ssrc = state->orig_ssrc = rtp_hdr->ssrc;
state->initialized = 1;
- } else if (state->seq_no + 1u != seq)
- state->lost_no = abs(seq - (state->seq_no + 1));
+ state->last_timestamp = timestamp;
+ } else if (state->ssrc != rtp_hdr->ssrc) {
+ state->ssrc = rtp_hdr->ssrc;
+ state->seq_offset = (state->seq_no + 1) - seq;
+ state->timestamp_offset = state->last_timestamp - timestamp;
+ LOGP(DMGCP, LOGL_NOTICE, "The SSRC changed... SSRC: %u offset: %d\n",
+ state->ssrc, state->seq_offset);
+ }
+ /* apply the offset and store it back to the packet */
+ seq += state->seq_offset;
+ rtp_hdr->sequence = htons(seq);
+ rtp_hdr->ssrc = state->orig_ssrc;
+
+ timestamp += state->timestamp_offset;
+ rtp_hdr->timestamp = htonl(timestamp);
+
+ /* seq changed, now compare if we have lost something */
+ if (state->seq_no + 1u != seq)
+ state->lost_no = abs(seq - (state->seq_no + 1));
state->seq_no = seq;
+ state->last_timestamp = timestamp;
+
if (payload < 0)
return;