audioaggregator: Always take first configure pad's rate and downstream caps into account when calculating allow sink caps

While we can convert between all formats apart from the rate, we
actually need to make sure that we comply with a) the rate of the first
configured pad and b) also all the allowed rates from downstream.

gst-libs/gst/audio/gstaudioaggregator.c

@@ -718,7 +718,6 @@ gst_audio_aggregator_sink_getcaps (GstPad * pad, GstAggregator * agg,
   GstCaps *sink_template_caps = gst_pad_get_pad_template_caps (pad);
   GstCaps *downstream_caps = gst_pad_get_allowed_caps (agg->srcpad);
   GstCaps *sink_caps;
-  GstStructure *s, *s2;
 
   GST_INFO_OBJECT (pad, "Getting caps with filter %" GST_PTR_FORMAT, filter);
   GST_DEBUG_OBJECT (pad, "sink template caps : %" GST_PTR_FORMAT,
@@ -774,41 +773,66 @@ gst_audio_aggregator_sink_getcaps (GstPad * pad, GstAggregator * agg,
   }
 
   /* Else we have a GstAudioAggregatorConvertPad and convert between all
-   * formats except for the sample rate, which has to match */
+   * formats except for the sample rate, which has to match.
-
-  sink_template_caps = gst_caps_make_writable (sink_template_caps);
-  s = gst_caps_get_structure (sink_template_caps, 0);
-
-  /* We will then use the rate in the first structure as the expected
-   * rate, we want to make sure only the compatible structures remain
-   * in downstream_caps
    */
-  if (downstream_caps && filter) {
+
-    GstCaps *tmp = gst_caps_intersect_full (downstream_caps, filter,
+  /* If we have a first configured pad, we can only convert everything except
+   * for the sample rate, so modify our template caps to have exactly that
+   * sample rate in all structures */
+  if (first_configured_pad) {
+    GST_INFO_OBJECT (pad, "first configured pad has sample rate %d",
+        first_configured_pad->info.rate);
+    sink_template_caps = gst_caps_make_writable (sink_template_caps);
+    gst_caps_set_simple (sink_template_caps, "rate", G_TYPE_INT,
+        first_configured_pad->info.rate, NULL);
+    gst_object_unref (first_configured_pad);
+  }
+
+  /* Now if we have downstream caps, filter against the template caps from
+   * above, i.e. with potentially fixated sample rate field already. This
+   * filters out any structures with unsupported rates.
+   *
+   * Afterwards we create new caps that only take over the rate fields of the
+   * remaining downstream caps, and filter that against the plain template
+   * caps to get the resulting allowed caps with conversion for everything but
+   * the rate */
+  if (downstream_caps) {
+    GstCaps *tmp;
+    guint i, n;
+
+    tmp =
+        gst_caps_intersect_full (sink_template_caps, downstream_caps,
         GST_CAPS_INTERSECT_FIRST);
 
-    gst_caps_unref (downstream_caps);
+    n = gst_caps_get_size (tmp);
-    downstream_caps = tmp;
+    sink_caps = gst_caps_new_empty ();
+    for (i = 0; i < n; i++) {
+      GstStructure *s = gst_caps_get_structure (tmp, i);
+      GstStructure *new_s =
+          gst_structure_new_empty (gst_structure_get_name (s));
+      gst_structure_set_value (new_s, "rate", gst_structure_get_value (s,
+              "rate"));
+      sink_caps = gst_caps_merge_structure (sink_caps, new_s);
+    }
+    gst_caps_unref (tmp);
+    tmp = sink_caps;
+
+    sink_caps =
+        gst_caps_intersect_full (sink_template_caps, tmp,
+        GST_CAPS_INTERSECT_FIRST);
+    gst_caps_unref (tmp);
+  } else {
+    sink_caps = gst_caps_ref (sink_template_caps);
   }
 
-  if (downstream_caps && !gst_caps_is_empty (downstream_caps))
+  /* And finally filter anything that remains against the filter caps */
-    s2 = gst_caps_get_structure (downstream_caps, 0);
+  if (filter) {
-  else
+    GstCaps *tmp =
-    s2 = NULL;
+        gst_caps_intersect_full (filter, sink_caps, GST_CAPS_INTERSECT_FIRST);
-
+    gst_caps_unref (sink_caps);
-  if (s2 && gst_structure_has_field (s2, "rate")) {
+    sink_caps = tmp;
-    gst_structure_set_value (s, "rate", gst_structure_get_value (s2, "rate"));
-  } else if (first_configured_pad) {
-    gst_structure_fixate_field_nearest_int (s, "rate",
-        first_configured_pad->info.rate);
   }
 
-  if (first_configured_pad)
-    gst_object_unref (first_configured_pad);
-
-  sink_caps = filter ? gst_caps_intersect (sink_template_caps,
-      filter) : gst_caps_ref (sink_template_caps);
-
   GST_INFO_OBJECT (pad, "returned sink caps : %" GST_PTR_FORMAT, sink_caps);
 
   gst_caps_unref (sink_template_caps);