RIST main profile RTP section

This branch provides the next step of the RIST specification. This is the RTP extensions from the main profile. Three is one extension to "compress" null MPEG-TS packets into a bitfield to reduce bandwidth. The other one is RTP sequence number extensions to extend them with an extra 16 bits.

What is not included in this branch is putting this extension into the jitterbuffer and actually allowing it to have more than 64k packets long. This will be in another MR later.

gst/rist/gstristrtpext.c

@@ -77,19 +77,89 @@ struct _GstRistRtpExt
   GstPad *srcpad, *sinkpad;
 
   gboolean drop_null;
-  gboolean seqnumext;
+  gboolean add_seqnumext;
+
+  guint32 extseqnum;
 };
 
 G_DEFINE_TYPE_WITH_CODE (GstRistRtpExt, gst_rist_rtp_ext, GST_TYPE_ELEMENT,
     GST_DEBUG_CATEGORY_INIT (gst_rist_rtp_ext_debug, "ristrtpext", 0,
         "RIST RTP Extension"));
 
+
+/*
+ * rtp_ext_seq:
+ * @extseq: (inout): a previous extended seqs
+ * @seq: a new seq
+ *
+ * Update the @extseq field with the extended seq of @seq
+ * For the first call of the method, @extseq should point to a location
+ * with a value of -1.
+ *
+ * This function is able to handle both forward and backward seqs taking
+ * into account:
+ *   - seq wraparound making sure that the returned value is properly increased.
+ *   - seq unwraparound making sure that the returned value is properly decreased.
+ *
+ * Returns: The extended seq of @seq or 0 if the result can't go anywhere backwards.
+ *
+ * NOTE: This is a calque of gst_rtp_buffer_ext_timestamp() but with
+ * s/32/16/ and s/64/32/ and s/0xffffffff/0xffff/ and s/timestamp/seqnum/.
+ */
+static guint32
+rtp_ext_seq (guint32 * extseqnum, guint16 seqnum)
+{
+  guint32 result, ext;
+
+  g_return_val_if_fail (extseqnum != NULL, -1);
+
+  ext = *extseqnum;
+
+  if (ext == -1) {
+    result = seqnum;
+  } else {
+    /* pick wraparound counter from previous seqnum and add to new seqnum */
+    result = seqnum + (ext & ~(0xffff));
+
+    /* check for seqnum wraparound */
+    if (result < ext) {
+      guint32 diff = ext - result;
+
+      if (diff > G_MAXINT16) {
+        /* seqnum went backwards more than allowed, we wrap around and get
+         * updated extended seqnum. */
+        result += (1 << 16);
+      }
+    } else {
+      guint32 diff = result - ext;
+
+      if (diff > G_MAXINT16) {
+        if (result < (1 << 16)) {
+          GST_WARNING
+              ("Cannot unwrap, any wrapping took place yet. Returning 0 without updating extended seqnum.");
+          return 0;
+        } else {
+          /* seqnum went forwards more than allowed, we unwrap around and get
+           * updated extended seqnum. */
+          result -= (1 << 16);
+          /* We don't want the extended seqnum storage to go back, ever */
+          return result;
+        }
+      }
+    }
+  }
+
+  *extseqnum = result;
+
+  return result;
+}
+
+
 static GstFlowReturn
 gst_rist_rtp_ext_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
 {
   GstRistRtpExt *self = GST_RIST_RTP_EXT (parent);
   GstRTPBuffer rtp = GST_RTP_BUFFER_INIT;
-  guint16 seqnumext_val = 0;
   gboolean drop_null = self->drop_null;
   gboolean ts_packet_size = 0;
   guint ts_packet_count = 0;
@@ -97,7 +167,7 @@ gst_rist_rtp_ext_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
   guint8 npd_bits = 0;
   gboolean num_packets_deleted = 0;
 
-  if (!self->drop_null && !self->seqnumext)
+  if (!self->drop_null && !self->add_seqnumext)
     return gst_pad_push (self->srcpad, buffer);
 
   if (self->drop_null) {
@@ -180,14 +250,21 @@ gst_rist_rtp_ext_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
   bits |= (npd_bits & 0x7F);
 
   gst_rtp_buffer_set_extension (&rtp, TRUE);
-  gst_rtp_buffer_set_extension_data (&rtp, bits, self->seqnumext ? 1 : 0);
+  gst_rtp_buffer_set_extension_data (&rtp, bits, self->add_seqnumext ? 1 : 0);
 
-  if (self->seqnumext) {
+  if (self->add_seqnumext) {
     guint8 *data;
     guint wordlen;
+    guint16 seqnum = gst_rtp_buffer_get_seq (&rtp);
+    guint32 extseqnum;
+
+    if (GST_BUFFER_IS_DISCONT (buffer))
+      self->extseqnum = -1;
+
+    extseqnum = rtp_ext_seq (&self->extseqnum, seqnum);
 
     gst_rtp_buffer_get_extension_data (&rtp, &bits, (void **) &data, &wordlen);
-    GST_WRITE_UINT16_BE (data, seqnumext_val);
+    GST_WRITE_UINT16_BE (data, (extseqnum >> 16));
     data[2] = data[3] = 0;
   }
 
@@ -212,6 +289,8 @@ error_mapped:
 static void
 gst_rist_rtp_ext_init (GstRistRtpExt * self)
 {
+  self->extseqnum = -1;
+
   self->sinkpad = gst_pad_new_from_static_template (&sink_templ,
       sink_templ.name_template);
   self->srcpad = gst_pad_new_from_static_template (&src_templ,
@@ -236,7 +315,7 @@ gst_rist_rtp_ext_get_property (GObject * object, guint prop_id,
       g_value_set_boolean (value, self->drop_null);
       break;
     case PROP_SEQUENCE_NUMBER_EXTENSION:
-      g_value_set_boolean (value, self->seqnumext);
+      g_value_set_boolean (value, self->add_seqnumext);
       break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
@@ -255,7 +334,7 @@ gst_rist_rtp_ext_set_property (GObject * object, guint prop_id,
       self->drop_null = g_value_get_boolean (value);
       break;
     case PROP_SEQUENCE_NUMBER_EXTENSION:
-      self->seqnumext = g_value_get_boolean (value);
+      self->add_seqnumext = g_value_get_boolean (value);
       break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);