From 87457a862d3f9e1468553d1e070e16746949a443 Mon Sep 17 00:00:00 2001
From: Havard Graff <havard@pexip.com>
Date: Sun, 20 Oct 2019 12:17:25 +0200
Subject: [PATCH] rtpjitterbuffer: make sure not to drop packets based on skew

One of the jitterbuffers functions is to try and make sense of weird
network behavior.

It is quite unhelpful for the jitterbuffer to start dropping packets
itself when what you are trying to achieve is better network resilience.

In the case of a skew, this could often mean the sender has restarted
in some fashion, and then dropping the very first buffer of this "new"
stream could often mean missing valuable information, like in the case
of video and I-frames.

This patch simply reverts back to the old behavior, prior to https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/commit/8d955fc32b552b2db933c67f3cfa31d987f36b81
and includes the simplest test I could write to demonstrate the behavior,
where a single packet arrives "perfectly", then a 50ms gap happens,
and then two more packets arrive in perfect order after that.

# Conflicts:
#	tests/check/elements/rtpjitterbuffer.c
---
 gst/rtpmanager/rtpjitterbuffer.c       |  4 ++--
 tests/check/elements/rtpjitterbuffer.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/gst/rtpmanager/rtpjitterbuffer.c b/gst/rtpmanager/rtpjitterbuffer.c
index 185f111..aeb2d07 100644
--- a/gst/rtpmanager/rtpjitterbuffer.c
+++ b/gst/rtpmanager/rtpjitterbuffer.c
@@ -955,8 +955,8 @@ rtp_jitter_buffer_calculate_pts (RTPJitterBuffer * jbuf, GstClockTime dts,
         GST_TIME_FORMAT ", reset jitterbuffer and discard", GST_TIME_ARGS (pts),
         jbuf->delay, GST_TIME_ARGS (dts));
     rtp_jitter_buffer_reset_skew (jbuf);
-    pts = GST_CLOCK_TIME_NONE;
-    goto done;
+    rtp_jitter_buffer_resync (jbuf, dts, gstrtptime, ext_rtptime, TRUE);
+    pts = dts;
   }
 
   jbuf->prev_out_time = pts;
diff --git a/tests/check/elements/rtpjitterbuffer.c b/tests/check/elements/rtpjitterbuffer.c
index cbb88ca..88ce187 100644
--- a/tests/check/elements/rtpjitterbuffer.c
+++ b/tests/check/elements/rtpjitterbuffer.c
@@ -2729,6 +2729,39 @@ GST_START_TEST (test_rtx_does_not_affect_pts_calculation)
 
 GST_END_TEST;
 
+GST_START_TEST (test_dont_drop_packet_based_on_skew)
+{
+  GstHarness *h = gst_harness_new ("rtpjitterbuffer");
+  guint base_seqnum;
+  GstClockTime now;
+  guint i;
+
+  /* set up a deterministic state and take the time on the clock */
+  g_object_set (h->element, "do-retransmission", TRUE, "do-lost", TRUE, NULL);
+  base_seqnum = construct_deterministic_initial_state (h, 20);
+  now = gst_clock_get_time (GST_ELEMENT_CLOCK (h->element));
+
+  /* and after a delay of 50ms... */
+  now += GST_MSECOND * 50;
+  gst_test_clock_set_time (GST_TEST_CLOCK (GST_ELEMENT_CLOCK (h->element)),
+      now);
+
+  /* ..two more buffers arrive in perfect order */
+  for (i = 0; i < 2; i++) {
+    gst_harness_push (h, generate_test_buffer_full (now + i * GST_MSECOND * 20,
+            base_seqnum + i, (base_seqnum + i) * TEST_RTP_TS_DURATION));
+  }
+
+  /* verify we did not drop any of them */
+  for (i = 0; i < 2; i++) {
+    gst_buffer_unref (gst_harness_pull (h));
+  }
+
+  gst_harness_teardown (h);
+}
+
+GST_END_TEST;
+
 GST_START_TEST (test_timer_queue_set_timer)
 {
   RtpTimerQueue *queue = rtp_timer_queue_new ();
@@ -3364,6 +3397,7 @@ rtpjitterbuffer_suite (void)
   tcase_add_test (tc_chain, test_minor_reorder_does_not_skew);
   tcase_add_loop_test (tc_chain, test_rtx_does_not_affect_pts_calculation, 0,
       G_N_ELEMENTS (rtx_does_not_affect_pts_calculation_input));
+  tcase_add_test (tc_chain, test_dont_drop_packet_based_on_skew);
 
   tcase_add_test (tc_chain, test_deadline_ts_offset);
   tcase_add_test (tc_chain, test_big_gap_seqnum);
-- 
2.7.4