rtph264pay: propagate the GST_BUFFER_FLAG_DELTA_UNIT flag

Downstream elements may be interested knowing if a RTP packet is the start
of a key frame (to implement a RTP extension as defined in the
ONVIF Streaming Spec for example).

We do this by checking the GST_BUFFER_FLAG_DELTA_UNIT flag we receive from
upstream and propagate it to the *first* RTP packet outputted to transfer this
buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=730563

gst/rtp/gstrtph264pay.c

@@ -166,6 +166,7 @@ gst_rtp_h264_pay_init (GstRtpH264Pay * rtph264pay)
       (GDestroyNotify) gst_buffer_unref);
   rtph264pay->last_spspps = -1;
   rtph264pay->spspps_interval = DEFAULT_CONFIG_INTERVAL;
+  rtph264pay->delta_unit = FALSE;
 
   rtph264pay->adapter = gst_adapter_new ();
 }
@@ -704,7 +705,8 @@ gst_rtp_h264_pay_decode_nal (GstRtpH264Pay * payloader,
 
 static GstFlowReturn
 gst_rtp_h264_pay_payload_nal (GstRTPBasePayload * basepayload,
-    GstBuffer * paybuf, GstClockTime dts, GstClockTime pts, gboolean end_of_au);
+    GstBuffer * paybuf, GstClockTime dts, GstClockTime pts, gboolean end_of_au,
+    gboolean delta_unit);
 
 static GstFlowReturn
 gst_rtp_h264_pay_send_sps_pps (GstRTPBasePayload * basepayload,
@@ -721,7 +723,7 @@ gst_rtp_h264_pay_send_sps_pps (GstRTPBasePayload * basepayload,
     GST_DEBUG_OBJECT (rtph264pay, "inserting SPS in the stream");
     /* resend SPS */
     ret = gst_rtp_h264_pay_payload_nal (basepayload, gst_buffer_ref (sps_buf),
-        dts, pts, FALSE);
+        dts, pts, FALSE, FALSE);
     /* Not critical here; but throw a warning */
     if (ret != GST_FLOW_OK) {
       sent_all_sps_pps = FALSE;
@@ -735,7 +737,7 @@ gst_rtp_h264_pay_send_sps_pps (GstRTPBasePayload * basepayload,
     GST_DEBUG_OBJECT (rtph264pay, "inserting PPS in the stream");
     /* resend PPS */
     ret = gst_rtp_h264_pay_payload_nal (basepayload, gst_buffer_ref (pps_buf),
-        dts, pts, FALSE);
+        dts, pts, FALSE, FALSE);
     /* Not critical here; but throw a warning */
     if (ret != GST_FLOW_OK) {
       sent_all_sps_pps = FALSE;
@@ -749,9 +751,12 @@ gst_rtp_h264_pay_send_sps_pps (GstRTPBasePayload * basepayload,
   return ret;
 }
 
+/* @delta_unit: if %FALSE the first packet sent won't have the
+ * GST_BUFFER_FLAG_DELTA_UNIT flag. */
 static GstFlowReturn
 gst_rtp_h264_pay_payload_nal (GstRTPBasePayload * basepayload,
-    GstBuffer * paybuf, GstClockTime dts, GstClockTime pts, gboolean end_of_au)
+    GstBuffer * paybuf, GstClockTime dts, GstClockTime pts, gboolean end_of_au,
+    gboolean delta_unit)
 {
   GstRtpH264Pay *rtph264pay;
   GstFlowReturn ret;
@@ -843,6 +848,12 @@ gst_rtp_h264_pay_payload_nal (GstRTPBasePayload * basepayload,
     GST_BUFFER_PTS (outbuf) = pts;
     GST_BUFFER_DTS (outbuf) = dts;
 
+    if (!delta_unit)
+      /* Only the first packet sent should not have the flag */
+      delta_unit = TRUE;
+    else
+      GST_BUFFER_FLAG_SET (outbuf, GST_BUFFER_FLAG_DELTA_UNIT);
+
     gst_rtp_buffer_unmap (&rtp);
 
     /* insert payload memory block */
@@ -909,6 +920,12 @@ gst_rtp_h264_pay_payload_nal (GstRTPBasePayload * basepayload,
           gst_buffer_copy_region (paybuf, GST_BUFFER_COPY_MEMORY, pos,
               limitedSize));
 
+      if (!delta_unit)
+        /* Only the first packet sent should not have the flag */
+        delta_unit = TRUE;
+      else
+        GST_BUFFER_FLAG_SET (outbuf, GST_BUFFER_FLAG_DELTA_UNIT);
+
       /* add the buffer to the buffer list */
       gst_buffer_list_add (list, outbuf);
 
@@ -940,6 +957,7 @@ gst_rtp_h264_pay_handle_buffer (GstRTPBasePayload * basepayload,
   gboolean avc;
   GstBuffer *paybuf = NULL;
   gsize skip;
+  gboolean delayed_not_delta_unit = FALSE;
 
   rtph264pay = GST_RTP_H264_PAY (basepayload);
 
@@ -956,11 +974,23 @@ gst_rtp_h264_pay_handle_buffer (GstRTPBasePayload * basepayload,
     size = map.size;
     pts = GST_BUFFER_PTS (buffer);
     dts = GST_BUFFER_DTS (buffer);
+    rtph264pay->delta_unit = GST_BUFFER_FLAG_IS_SET (buffer,
+        GST_BUFFER_FLAG_DELTA_UNIT);
     GST_DEBUG_OBJECT (basepayload, "got %" G_GSIZE_FORMAT " bytes", size);
   } else {
     dts = gst_adapter_prev_dts (rtph264pay->adapter, NULL);
     pts = gst_adapter_prev_pts (rtph264pay->adapter, NULL);
     if (buffer) {
+      if (!GST_BUFFER_FLAG_IS_SET (buffer, GST_BUFFER_FLAG_DELTA_UNIT)) {
+        if (gst_adapter_available (rtph264pay->adapter) == 0)
+          rtph264pay->delta_unit = FALSE;
+        else
+          /* This buffer contains a key frame but the adapter isn't empty. So
+           * we'll purge it first by sending a first packet and then the second
+           * one won't have the DELTA_UNIT flag. */
+          delayed_not_delta_unit = TRUE;
+      }
+
       if (!GST_CLOCK_TIME_IS_VALID (dts))
         dts = GST_BUFFER_DTS (buffer);
       if (!GST_CLOCK_TIME_IS_VALID (pts))
@@ -1024,7 +1054,12 @@ gst_rtp_h264_pay_handle_buffer (GstRTPBasePayload * basepayload,
           nal_len);
       ret =
           gst_rtp_h264_pay_payload_nal (basepayload, paybuf, dts, pts,
-          end_of_au);
+          end_of_au, rtph264pay->delta_unit);
+
+      if (!rtph264pay->delta_unit)
+        /* Only the first outgoing packet doesn't have the DELTA_UNIT flag */
+        rtph264pay->delta_unit = TRUE;
+
       if (ret != GST_FLOW_OK)
         break;
 
@@ -1155,7 +1190,16 @@ gst_rtp_h264_pay_handle_buffer (GstRTPBasePayload * basepayload,
       /* put the data in one or more RTP packets */
       ret =
           gst_rtp_h264_pay_payload_nal (basepayload, paybuf, dts, pts,
-          end_of_au);
+          end_of_au, rtph264pay->delta_unit);
+
+      if (delayed_not_delta_unit) {
+        rtph264pay->delta_unit = FALSE;
+        delayed_not_delta_unit = FALSE;
+      } else {
+        /* Only the first outgoing packet doesn't have the DELTA_UNIT flag */
+        rtph264pay->delta_unit = TRUE;
+      }
+
       if (ret != GST_FLOW_OK) {
         break;
       }

gst/rtp/gstrtph264pay.h

@@ -74,6 +74,9 @@ struct _GstRtpH264Pay
   guint spspps_interval;
   gboolean send_spspps;
   GstClockTime last_spspps;
+
+  /* TRUE if the next NALU processed should have the DELTA_UNIT flag */
+  gboolean delta_unit;
 };
 
 struct _GstRtpH264PayClass