From 01469a7de50b5a4dc01e059bd42b11ee0f3a0cde Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Fri, 11 Aug 2023 13:06:24 +0300
Subject: [PATCH] rtpgstpay: Delay pushing of event packets until the next
 buffer

And also re-timestamp them with the current buffer's PTS.

Not doing so keeps the timestamps of event packets as
GST_CLOCK_TIME_NONE or the timestamp of the previous buffer, both of
which are bogus.

Making sure that (especially) the first packet has a valid timestamp
allows putting e.g. the NTP timestamp RTP header extension on it.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6294>
---
 .../gst-plugins-good/gst/rtp/gstrtpgstpay.c   | 36 +++++++++++--------
 .../gst-plugins-good/gst/rtp/gstrtpgstpay.h   |  2 --
 2 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.c b/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.c
index 5dba040bf0..71e89e41bf 100644
--- a/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.c
+++ b/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.c
@@ -182,7 +182,6 @@ gst_rtp_gst_pay_reset (GstRtpGSTPay * rtpgstpay, gboolean full)
     rtpgstpay->current_CV = 0;
     rtpgstpay->next_CV = 0;
   }
-  rtpgstpay->received_buffer = FALSE;
 }
 
 static void
@@ -366,6 +365,16 @@ gst_rtp_gst_pay_create_from_adapter (GstRtpGSTPay * rtpgstpay,
   return TRUE;
 }
 
+static gboolean
+retimestamp_buffer (GstBuffer ** buffer, guint idx, gpointer user_data)
+{
+  GstClockTime *timestamp = user_data;
+
+  GST_BUFFER_PTS (*buffer) = *timestamp;
+
+  return TRUE;
+}
+
 static GstFlowReturn
 gst_rtp_gst_pay_flush (GstRtpGSTPay * rtpgstpay, GstClockTime timestamp)
 {
@@ -373,13 +382,14 @@ gst_rtp_gst_pay_flush (GstRtpGSTPay * rtpgstpay, GstClockTime timestamp)
 
   gst_rtp_gst_pay_create_from_adapter (rtpgstpay, timestamp);
 
-  if (!rtpgstpay->received_buffer) {
-    GST_DEBUG_OBJECT (rtpgstpay,
-        "Can't flush without having received a buffer yet");
-    return GST_FLOW_OK;
-  }
-
   if (rtpgstpay->pending_buffers) {
+    // make sure all buffers in the buffer list have the correct timestamp.
+    // If we created packets based on an event they would have
+    // GST_CLOCK_TIME_NONE as PTS.
+
+    gst_buffer_list_foreach (rtpgstpay->pending_buffers, retimestamp_buffer,
+        &timestamp);
+
     /* push the whole buffer list at once */
     ret = gst_rtp_base_payload_push_list (GST_RTP_BASE_PAYLOAD (rtpgstpay),
         rtpgstpay->pending_buffers);
@@ -584,12 +594,10 @@ gst_rtp_gst_pay_sink_event (GstRTPBasePayload * payload, GstEvent * event)
     GST_DEBUG_OBJECT (rtpgstpay, "make event type %d for %s",
         etype, GST_EVENT_TYPE_NAME (event));
     gst_rtp_gst_pay_send_event (rtpgstpay, etype, event);
-    /* Do not send stream-start right away since caps/new-segment were not yet
-       sent, so our data would be considered invalid */
-    if (etype != 4) {
-      /* flush the adapter immediately */
-      gst_rtp_gst_pay_flush (rtpgstpay, GST_CLOCK_TIME_NONE);
-    }
+    // do not flush events here yet as they would get no timestamp at all or
+    // the timestamp of the previous buffer, both of which are bogus. We need
+    // to wait until the next actual input frame to know the timestamp that
+    // applies to the event.
   }
 
   gst_event_unref (event);
@@ -654,8 +662,6 @@ gst_rtp_gst_pay_handle_buffer (GstRTPBasePayload * basepayload,
 
   rtpgstpay = GST_RTP_GST_PAY (basepayload);
 
-  rtpgstpay->received_buffer = TRUE;
-
   timestamp = GST_BUFFER_PTS (buffer);
   running_time =
       gst_segment_to_running_time (&basepayload->segment, GST_FORMAT_TIME,
diff --git a/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.h b/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.h
index 671186bf70..3db3d61694 100644
--- a/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.h
+++ b/subprojects/gst-plugins-good/gst/rtp/gstrtpgstpay.h
@@ -57,8 +57,6 @@ struct _GstRtpGSTPay
   guint config_interval;
   GstClockTime last_config;
   gboolean force_config;
-
-  gboolean received_buffer;
 };
 
 struct _GstRtpGSTPayClass