rtpjitterbuffer: Always estimate DTS from the current clock time

Estimating it from the RTP time will give us the PTS, so in cases of PTS!=DTS
we would produce wrong DTS. As now the estimated DTS is based on the clock,
don't store it in the jitterbuffer items as it would otherwise be used in the
skew calculations and would influence the results. We only really need the DTS
for timer calculations.

https://bugzilla.gnome.org/show_bug.cgi?id=749536

diff --git a/gst/rtpmanager/gstrtpjitterbuffer.c b/gst/rtpmanager/gstrtpjitterbuffer.c
index 673a5ad..4fc1fb8 100644 (file)
--- a/gst/rtpmanager/gstrtpjitterbuffer.c
+++ b/gst/rtpmanager/gstrtpjitterbuffer.c
@@ -2335,6 +2335,28 @@ handle_big_gap_buffer (GstRtpJitterBuffer * jitterbuffer, gboolean future,
   return reset;
 }
 
+static GstClockTime
+get_current_running_time (GstRtpJitterBuffer * jitterbuffer)
+{
+  GstClock *clock = gst_element_get_clock (GST_ELEMENT_CAST (jitterbuffer));
+  GstClockTime running_time = GST_CLOCK_TIME_NONE;
+
+  if (clock) {
+    GstClockTime base_time =
+        gst_element_get_base_time (GST_ELEMENT_CAST (jitterbuffer));
+    GstClockTime clock_time = gst_clock_get_time (clock);
+
+    if (clock_time > base_time)
+      running_time = clock_time - base_time;
+    else
+      running_time = 0;
+
+    gst_object_unref (clock);
+  }
+
+  return running_time;
+}
+
 static GstFlowReturn
 gst_rtp_jitter_buffer_chain (GstPad * pad, GstObject * parent,
     GstBuffer * buffer)
@@ -2353,6 +2375,7 @@ gst_rtp_jitter_buffer_chain (GstPad * pad, GstObject * parent,
   gboolean do_next_seqnum = FALSE;
   RTPJitterBufferItem *item;
   GstMessage *msg = NULL;
+  gboolean estimated_dts = FALSE;
 
   jitterbuffer = GST_RTP_JITTER_BUFFER_CAST (parent);
 
@@ -2374,12 +2397,20 @@ gst_rtp_jitter_buffer_chain (GstPad * pad, GstObject * parent,
   else if (pts == -1)
     pts = dts;
 
-  /* take the DTS of the buffer. This is the time when the packet was
-   * received and is used to calculate jitter and clock skew. We will adjust
-   * this DTS with the smoothed value after processing it in the
-   * jitterbuffer and assign it as the PTS. */
-  /* bring to running time */
-  dts = gst_segment_to_running_time (&priv->segment, GST_FORMAT_TIME, dts);
+  if (dts == -1) {
+    /* If we have no DTS here, i.e. no capture time, get one from the
+     * clock now to have something to calculate with in the future. */
+    dts = get_current_running_time (jitterbuffer);
+    pts = dts;
+    estimated_dts = TRUE;
+  } else {
+    /* take the DTS of the buffer. This is the time when the packet was
+     * received and is used to calculate jitter and clock skew. We will adjust
+     * this DTS with the smoothed value after processing it in the
+     * jitterbuffer and assign it as the PTS. */
+    /* bring to running time */
+    dts = gst_segment_to_running_time (&priv->segment, GST_FORMAT_TIME, dts);
+  }
 
   GST_DEBUG_OBJECT (jitterbuffer,
       "Received packet #%d at time %" GST_TIME_FORMAT ", discont %d", seqnum,
@@ -2453,34 +2484,6 @@ gst_rtp_jitter_buffer_chain (GstPad * pad, GstObject * parent,
     GST_DEBUG_OBJECT (jitterbuffer, "expected #%d, got #%d, gap of %d",
         expected, seqnum, gap);
 
-    /* Try to calculate a DTS if we have none, based on
-     * whatever the jitterbuffer currently knows */
-    if (dts == GST_CLOCK_TIME_NONE) {
-      guint64 base_rtptime, base_time;
-      guint32 clock_rate;
-      guint64 last_rtptime;
-      guint64 ext_rtptime;
-      GstClockTime gst_send_diff;
-      guint64 send_diff;
-
-      rtp_jitter_buffer_get_sync (jitterbuffer->priv->jbuf, &base_rtptime,
-          &base_time, &clock_rate, &last_rtptime);
-
-      if (base_rtptime != -1 && clock_rate != -1 && base_time != -1) {
-        ext_rtptime = gst_rtp_buffer_ext_timestamp (&last_rtptime, rtptime);
-        if (ext_rtptime > base_rtptime)
-          send_diff = ext_rtptime - base_rtptime;
-        else
-          send_diff = 0;
-
-        gst_send_diff =
-            gst_util_uint64_scale_int (send_diff, GST_SECOND, clock_rate);
-
-        dts = base_time + gst_send_diff;
-        pts = dts;
-      }
-    }
-
     if (G_LIKELY (gap == 0)) {
       /* packet is expected */
       calculate_packet_spacing (jitterbuffer, rtptime, dts);
@@ -2587,27 +2590,6 @@ gst_rtp_jitter_buffer_chain (GstPad * pad, GstObject * parent,
   } else {
     GST_DEBUG_OBJECT (jitterbuffer, "First buffer #%d", seqnum);
 
-    /* If we have no DTS here, i.e. no capture time, get one from the
-     * clock now to have something to calculate with in the future.
-     */
-    if (dts == GST_CLOCK_TIME_NONE) {
-      GstClock *clock = gst_element_get_clock (GST_ELEMENT_CAST (jitterbuffer));
-
-      if (clock) {
-        GstClockTime base_time =
-            gst_element_get_base_time (GST_ELEMENT_CAST (jitterbuffer));
-        GstClockTime clock_time = gst_clock_get_time (clock);
-
-        if (clock_time > base_time)
-          dts = clock_time - base_time;
-        else
-          dts = 0;
-        pts = dts;
-
-        gst_object_unref (clock);
-      }
-    }
-
     /* we don't know what the next_in_seqnum should be, wait for the last
      * possible moment to push this buffer, maybe we get an earlier seqnum
      * while we wait */
@@ -2674,7 +2656,16 @@ gst_rtp_jitter_buffer_chain (GstPad * pad, GstObject * parent,
     }
   }
 
-  item = alloc_item (buffer, ITEM_TYPE_BUFFER, dts, pts, seqnum, 1, rtptime);
+  /* If we estimated the DTS, don't consider it in the clock skew calculations
+   * later. The code above always sets dts to pts or the other way around if
+   * any of those is valid in the buffer, so we know that if we estimated the
+   * dts that both are unknown */
+  if (estimated_dts)
+    item =
+        alloc_item (buffer, ITEM_TYPE_BUFFER, GST_CLOCK_TIME_NONE,
+        GST_CLOCK_TIME_NONE, seqnum, 1, rtptime);
+  else
+    item = alloc_item (buffer, ITEM_TYPE_BUFFER, dts, pts, seqnum, 1, rtptime);
 
   /* now insert the packet into the queue in sorted order. This function returns
    * FALSE if a packet with the same seqnum was already in the queue, meaning we