res_rtp_asterisk: Don't use double math to generate timestamps

Rounding issues with double math were causing rtp timestamp
slips in outgoing packets.  We're now back to integer math
and are getting no more slips.

ASTERISK-30391

Change-Id: I6ba992b49ffdf9ebea074581dfa784a188c661a4

diff --git a/res/res_rtp_asterisk.c b/res/res_rtp_asterisk.c
index da0a3b97ac23dda2997c01d85c0a4ed6678fa43a..bd4c1f7531165c4789401777fd348f951c56169b 100644 (file)
--- a/res/res_rtp_asterisk.c
+++ b/res/res_rtp_asterisk.c
@@ -442,6 +442,7 @@ struct ast_rtp {
        int send_payload;
        int send_duration;
        unsigned int flags;
+       struct timeval rxcore;
        struct timeval txcore;
 
        struct timeval dtmfmute;
@@ -5496,10 +5497,10 @@ static void calc_rxstamp_and_jitter(struct timeval *tv,
 {
        int rate = ast_rtp_get_rate(rtp->f.subclass.format);
 
-       double estimated_elapsed;
        double jitter = 0.0;
        double prev_jitter = 0.0;
        struct timeval now;
+       struct timeval tmp;
        double rxnow;
        double arrival_sec;
        unsigned int arrival;
@@ -5512,9 +5513,22 @@ static void calc_rxstamp_and_jitter(struct timeval *tv,
                rtp->rxstart = ast_tv2double(&now);
                rtp->remote_seed_rx_rtp_ts = rx_rtp_ts;
 
-               /* Round to 0.1ms for nice, pretty timestamps */
-               rtp->rxstart = floor( rtp->rxstart * 10000.0 ) / 10000.0;
-               *tv = ast_double2tv(rtp->rxstart);
+               /*
+                * "tv" is placed in the received frame's
+                * "delivered" field and when this frame is
+                * sent out again on the other side, it's
+                * used to calculate the timestamp on the
+                * outgoing RTP packets.
+                *
+                * NOTE: We need to do integer math here
+                * because double math rounding issues can
+                * generate incorrect timestamps.
+                */
+               rtp->rxcore = now;
+               tmp = ast_samp2tv(rx_rtp_ts, rate);
+               rtp->rxcore = ast_tvsub(rtp->rxcore, tmp);
+               rtp->rxcore.tv_usec -= rtp->rxcore.tv_usec % 100;
+               *tv = ast_tvadd(rtp->rxcore, tmp);
 
                ast_debug_rtcp(3, "%s: "
                        "Seed ts: %u current time: %f\n",
@@ -5526,8 +5540,14 @@ static void calc_rxstamp_and_jitter(struct timeval *tv,
                return;
        }
 
-       estimated_elapsed = ast_samp2sec(rx_rtp_ts - rtp->remote_seed_rx_rtp_ts, rate);
-       *tv = ast_double2tv(rtp->rxstart + estimated_elapsed);
+       tmp = ast_samp2tv(rx_rtp_ts, rate);
+       /* See the comment about "tv" above. Even if
+        * we don't use this received packet for jitter
+        * calculations, we still need to set tv so the
+        * timestamp will be correct when this packet is
+        * sent out again.
+        */
+       *tv = ast_tvadd(rtp->rxcore, tmp);
 
        /*
         * The first few packets are generally unstable so let's