From 3113e341eac26b1766ad01a04db690926b12d165 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Fri, 5 Jun 2015 16:44:08 +0200
Subject: [PATCH] rtpbasepayload: Always prefer downstream's ssrc suggestion if
 any

Otherwise ssrc changes via rtpsession's (deprecated!) internal-ssrc property
are not possible anymore. rtpsession was now patched to only suggest an ssrc
if it makes sense to do so.

In 2.0 we should get rid of all the properties that are also negotiated via
caps, the code and behaviour is too confusing otherwise.

https://bugzilla.gnome.org/show_bug.cgi?id=749581
---
 gst-libs/gst/rtp/gstrtpbasepayload.c | 66 ++++++++++------------------
 1 file changed, 24 insertions(+), 42 deletions(-)

diff --git a/gst-libs/gst/rtp/gstrtpbasepayload.c b/gst-libs/gst/rtp/gstrtpbasepayload.c
index d620be7fdb..393d8c6751 100644
--- a/gst-libs/gst/rtp/gstrtpbasepayload.c
+++ b/gst-libs/gst/rtp/gstrtpbasepayload.c
@@ -808,7 +808,7 @@ gst_rtp_base_payload_negotiate (GstRTPBasePayload * payload)
     GstCaps *temp;
     GstStructure *s, *d;
     const GValue *value;
-    gboolean have_pt = FALSE, have_ssrc = FALSE;
+    gboolean have_pt = FALSE;
     gboolean have_ts_offset = FALSE;
     gboolean have_seqnum_offset = FALSE;
     guint max_ptime, ptime;
@@ -824,11 +824,19 @@ gst_rtp_base_payload_negotiate (GstRTPBasePayload * payload)
       return FALSE;
     }
 
-    /* We prefer the pt, ssrc, timestamp-offset, seqnum-offset from the
+    /* We prefer the pt, timestamp-offset, seqnum-offset from the
      * property (if set), or any previously configured value over what
      * downstream prefers. Only if downstream can't accept that, or the
      * properties were not set, we fall back to choosing downstream's
      * preferred value
+     *
+     * For ssrc we prefer any value downstream suggests, otherwise
+     * the property value or as a last resort a random value.
+     * This difference for ssrc is implemented for retaining backwards
+     * compatibility with changing rtpsession's internal-ssrc property.
+     *
+     * FIXME 2.0: All these properties should go away and be negotiated
+     * via caps only!
      */
 
     /* try to use the previously set pt, or the one from the property */
@@ -883,49 +891,23 @@ gst_rtp_base_payload_negotiate (GstRTPBasePayload * payload)
       s = NULL;
     }
 
-    /* try to select the previously used ssrc, or the one from the property */
-    if (!payload->priv->ssrc_random
-        || gst_pad_has_current_caps (payload->srcpad)) {
-      GstCaps *probe_caps = gst_caps_copy (templ);
-      GstCaps *intersection;
-
-      gst_caps_set_simple (probe_caps, "ssrc", G_TYPE_UINT,
-          payload->current_ssrc, NULL);
-      intersection = gst_caps_intersect (probe_caps, temp);
-
-      if (!gst_caps_is_empty (intersection)) {
-        GST_LOG_OBJECT (payload, "Using selected ssrc %08x",
-            payload->current_ssrc);
-        gst_caps_unref (temp);
-        temp = intersection;
-        have_ssrc = TRUE;
-      } else {
-        GST_WARNING_OBJECT (payload, "Can't use selected ssrc %08x",
-            payload->current_ssrc);
-        gst_caps_unref (intersection);
-      }
-      gst_caps_unref (probe_caps);
-    }
-
     /* If we got no ssrc above, select one now */
-    if (!have_ssrc) {
-      /* get first structure */
-      s = gst_caps_get_structure (temp, 0);
+    /* get first structure */
+    s = gst_caps_get_structure (temp, 0);
 
-      if (gst_structure_has_field_typed (s, "ssrc", G_TYPE_UINT)) {
-        value = gst_structure_get_value (s, "ssrc");
-        payload->current_ssrc = g_value_get_uint (value);
-        GST_LOG_OBJECT (payload, "using peer ssrc %08x", payload->current_ssrc);
-      } else {
-        /* FIXME, fixate_nearest_uint would be even better but we
-         * don't support uint ranges so how likely is it that anybody
-         * uses a list of possible ssrcs */
-        gst_structure_set (s, "ssrc", G_TYPE_UINT, payload->current_ssrc, NULL);
-        GST_LOG_OBJECT (payload, "using internal ssrc %08x",
-            payload->current_ssrc);
-      }
-      s = NULL;
+    if (gst_structure_has_field_typed (s, "ssrc", G_TYPE_UINT)) {
+      value = gst_structure_get_value (s, "ssrc");
+      payload->current_ssrc = g_value_get_uint (value);
+      GST_LOG_OBJECT (payload, "using peer ssrc %08x", payload->current_ssrc);
+    } else {
+      /* FIXME, fixate_nearest_uint would be even better but we
+       * don't support uint ranges so how likely is it that anybody
+       * uses a list of possible ssrcs */
+      gst_structure_set (s, "ssrc", G_TYPE_UINT, payload->current_ssrc, NULL);
+      GST_LOG_OBJECT (payload, "using internal ssrc %08x",
+          payload->current_ssrc);
     }
+    s = NULL;
 
     /* try to select the previously used timestamp-offset, or the one from the property */
     if (!payload->priv->ts_offset_random