From f440b074b1b4054c6506ee6fd9f898d7925b1fb0 Mon Sep 17 00:00:00 2001
From: Havard Graff <havard.graff@gmail.com>
Date: Thu, 11 Aug 2016 23:07:44 +0200
Subject: [PATCH] rtpjitterbuffer: improved rtx-rtt averaging

The basic idea is this:
1. For *larger* rtx-rtt, weigh a new measurement as before
2. For *smaller* rtx-rtt, be a bit more conservative and weigh a bit less
3. For very large measurements, consider them "outliers"
   and count them a lot less

The idea being that reducing the rtx-rtt is much more harmful then
increasing it, since we don't want to be underestimating the rtt of the
network, and when using this number to estimate the latency you need for
you jitterbuffer, you would rather want it to be a bit larger then a bit
smaller, potentially losing rtx-packets. The "outlier-detector" is there
to prevent a single skewed measurement to affect the outcome too much.
On wireless networks, these are surprisingly common.

https://bugzilla.gnome.org/show_bug.cgi?id=769768
---
 gst/rtpmanager/gstrtpjitterbuffer.c    | 31 ++++++++++++++++++++++----
 tests/check/elements/rtpjitterbuffer.c |  2 +-
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/gst/rtpmanager/gstrtpjitterbuffer.c b/gst/rtpmanager/gstrtpjitterbuffer.c
index 5b372ea386..1a71947dc7 100644
--- a/gst/rtpmanager/gstrtpjitterbuffer.c
+++ b/gst/rtpmanager/gstrtpjitterbuffer.c
@@ -3543,6 +3543,32 @@ get_rtx_retry_period (GstRtpJitterBufferPrivate * priv,
   return rtx_retry_period;
 }
 
+/*
+  1. For *larger* rtx-rtt, weigh a new measurement as before (1/8th)
+  2. For *smaller* rtx-rtt, be a bit more conservative and weigh a bit less (1/16th)
+  3. For very large measurements (> avg * 2), consider them "outliers"
+     and count them a lot less (1/48th)
+*/
+static void
+update_avg_rtx_rtt (GstRtpJitterBufferPrivate * priv, GstClockTime rtt)
+{
+  gint weight;
+
+  if (priv->avg_rtx_rtt == 0) {
+    priv->avg_rtx_rtt = rtt;
+    return;
+  }
+
+  if (rtt > 2 * priv->avg_rtx_rtt)
+    weight = 48;
+  else if (rtt > priv->avg_rtx_rtt)
+    weight = 8;
+  else
+    weight = 16;
+
+  priv->avg_rtx_rtt = (rtt + (weight - 1) * priv->avg_rtx_rtt) / weight;
+}
+
 static void
 update_rtx_stats (GstRtpJitterBuffer * jitterbuffer, TimerData * timer,
     GstClockTime dts, gboolean success)
@@ -3574,10 +3600,7 @@ update_rtx_stats (GstRtpJitterBuffer * jitterbuffer, TimerData * timer,
   if (timer->num_rtx_retry == timer->num_rtx_received &&
       dts != GST_CLOCK_TIME_NONE && dts > timer->rtx_last) {
     delay = dts - timer->rtx_last;
-    if (priv->avg_rtx_rtt == 0)
-      priv->avg_rtx_rtt = delay;
-    else
-      priv->avg_rtx_rtt = (delay + 7 * priv->avg_rtx_rtt) / 8;
+    update_avg_rtx_rtt (priv, delay);
   } else {
     delay = 0;
   }
diff --git a/tests/check/elements/rtpjitterbuffer.c b/tests/check/elements/rtpjitterbuffer.c
index 5e41def6d3..a2d50d9297 100644
--- a/tests/check/elements/rtpjitterbuffer.c
+++ b/tests/check/elements/rtpjitterbuffer.c
@@ -1796,7 +1796,7 @@ GST_START_TEST (test_rtx_duplicate_packet_updates_rtx_stats)
               "rtx-per-packet", G_TYPE_DOUBLE, 1.0,
               "rtx-rtt", G_TYPE_UINT64, (guint64)
               /* Use the rtx-rtt formula. Can be subject to change though. */
-              ((now - rtx_request_6) + 7 * (now - rtx_request_7)) / 8, NULL)));
+              ((now - rtx_request_6) + 47 * (now - rtx_request_7)) / 48, NULL)));
 
   gst_object_unref (testclock);
   gst_harness_teardown (h);