From 2142edd3991bd9f41e4082588fa9a6f351e6b68a Mon Sep 17 00:00:00 2001
From: Arnout Vandecappelle <arnout@mind.be>
Date: Tue, 23 Dec 2008 11:39:59 +0000
Subject: [PATCH] gst/rtpmanager/rtpjitterbuffer.*: Keep track of the last
 outgoing timestamp and of the last sender-side time.  Timest...

Original commit message from CVS:
Patch by: Arnout Vandecappelle <arnout at mind dot be>
* gst/rtpmanager/rtpjitterbuffer.c: (rtp_jitter_buffer_reset_skew),
(calculate_skew):
* gst/rtpmanager/rtpjitterbuffer.h:
Keep track of the last outgoing timestamp and of the last sender-side
time.  Timestamps can only go forward if they do at the sender
side, can only go back if they do at the sender side, and remain the
same if they remain the same at the sender side. Fixes #565319.
---
 gst/rtpmanager/rtpjitterbuffer.c | 33 ++++++++++++++++++++++++++++++--
 gst/rtpmanager/rtpjitterbuffer.h |  1 +
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/gst/rtpmanager/rtpjitterbuffer.c b/gst/rtpmanager/rtpjitterbuffer.c
index d027dc2e96..52b774b6b8 100644
--- a/gst/rtpmanager/rtpjitterbuffer.c
+++ b/gst/rtpmanager/rtpjitterbuffer.c
@@ -113,6 +113,7 @@ rtp_jitter_buffer_reset_skew (RTPJitterBuffer * jbuf)
   jbuf->window_min = 0;
   jbuf->skew = 0;
   jbuf->prev_send_diff = -1;
+  jbuf->prev_out_time = -1;
   GST_DEBUG ("reset skew correction");
 }
 
@@ -198,16 +199,20 @@ calculate_skew (RTPJitterBuffer * jbuf, guint32 rtptime, GstClockTime time,
     jbuf->base_time = -1;
     jbuf->base_rtptime = -1;
     jbuf->clock_rate = clock_rate;
+    jbuf->prev_out_time = -1;
+    jbuf->prev_send_diff = -1;
   }
 
   /* first time, lock on to time and gstrtptime */
   if (G_UNLIKELY (jbuf->base_time == -1)) {
     jbuf->base_time = time;
+    jbuf->prev_out_time = -1;
     GST_DEBUG ("Taking new base time %" GST_TIME_FORMAT, GST_TIME_ARGS (time));
   }
   if (G_UNLIKELY (jbuf->base_rtptime == -1)) {
     jbuf->base_rtptime = gstrtptime;
     jbuf->base_extrtp = ext_rtptime;
+    jbuf->prev_send_diff = -1;
     GST_DEBUG ("Taking new base rtptime %" GST_TIME_FORMAT,
         GST_TIME_ARGS (gstrtptime));
   }
@@ -221,6 +226,8 @@ calculate_skew (RTPJitterBuffer * jbuf, guint32 rtptime, GstClockTime time,
     jbuf->base_time = time;
     jbuf->base_rtptime = gstrtptime;
     jbuf->base_extrtp = ext_rtptime;
+    jbuf->prev_out_time = -1;
+    jbuf->prev_send_diff = -1;
     send_diff = 0;
   }
 
@@ -253,6 +260,8 @@ calculate_skew (RTPJitterBuffer * jbuf, guint32 rtptime, GstClockTime time,
     jbuf->base_time = time;
     jbuf->base_rtptime = gstrtptime;
     jbuf->base_extrtp = ext_rtptime;
+    jbuf->prev_out_time = -1;
+    jbuf->prev_send_diff = -1;
     send_diff = 0;
     delta = 0;
   }
@@ -333,11 +342,31 @@ calculate_skew (RTPJitterBuffer * jbuf, guint32 rtptime, GstClockTime time,
 no_skew:
   /* the output time is defined as the base timestamp plus the RTP time
    * adjusted for the clock skew .*/
-  if (jbuf->base_time != -1)
+  if (jbuf->base_time != -1) {
     out_time = jbuf->base_time + send_diff + jbuf->skew;
-  else
+    /* check if timestamps are not going backwards, we can only check this if we
+     * have a previous out time and a previous send_diff */
+    if (G_LIKELY (jbuf->prev_out_time != -1 && jbuf->prev_send_diff != -1)) {
+      /* now check for backwards timestamps */
+      if (G_UNLIKELY (
+              /* if the server timestamps went up and the out_time backwards */
+              (send_diff > jbuf->prev_send_diff
+                  && out_time < jbuf->prev_out_time) ||
+              /* if the server timestamps went backwards and the out_time forwards */
+              (send_diff < jbuf->prev_send_diff
+                  && out_time > jbuf->prev_out_time) ||
+              /* if the server timestamps did not change */
+              send_diff == jbuf->prev_send_diff)) {
+        GST_DEBUG ("backwards timestamps, using previous time");
+        out_time = jbuf->prev_out_time;
+      }
+    }
+  } else
     out_time = -1;
 
+  jbuf->prev_out_time = out_time;
+  jbuf->prev_send_diff = send_diff;
+
   GST_DEBUG ("skew %" G_GINT64_FORMAT ", out %" GST_TIME_FORMAT,
       jbuf->skew, GST_TIME_ARGS (out_time));
 
diff --git a/gst/rtpmanager/rtpjitterbuffer.h b/gst/rtpmanager/rtpjitterbuffer.h
index aa00919045..ff1a16b076 100644
--- a/gst/rtpmanager/rtpjitterbuffer.h
+++ b/gst/rtpmanager/rtpjitterbuffer.h
@@ -58,6 +58,7 @@ struct _RTPJitterBuffer {
   GstClockTime   base_rtptime;
   guint32        clock_rate;
   GstClockTime   base_extrtp;
+  GstClockTime   prev_out_time;
   guint64        ext_rtptime;
   guint64        last_rtptime;
   gint64         window[RTP_JITTER_BUFFER_MAX_WINDOW];