switchbin: Add docs

Add documentation clauses and enrol switchbin to generate
plugin docs

docs/plugins/gst_plugins_cache.json

@@ -46771,6 +46771,82 @@
         "tracers": {},
         "url": "Unknown package origin"
     },
+    "switchbin": {
+        "description": "switchbin",
+        "elements": {
+            "switchbin": {
+                "author": "Carlos Rafael Giani <dv@pseudoterminal.org>",
+                "description": "Switch between sub-pipelines (paths) based on input caps",
+                "hierarchy": [
+                    "GstSwitchBin",
+                    "GstBin",
+                    "GstElement",
+                    "GstObject",
+                    "GInitiallyUnowned",
+                    "GObject"
+                ],
+                "klass": "Generic/Bin",
+                "long-name": "switchbin",
+                "pad-templates": {
+                    "sink": {
+                        "caps": "ANY",
+                        "direction": "sink",
+                        "presence": "always"
+                    },
+                    "src": {
+                        "caps": "ANY",
+                        "direction": "src",
+                        "presence": "always"
+                    }
+                },
+                "properties": {
+                    "async-handling": {
+                        "blurb": "The bin will handle Asynchronous state changes",
+                        "construct": false,
+                        "construct-only": false,
+                        "default": "false",
+                        "type-name": "gboolean",
+                        "writable": true
+                    },
+                    "current-path": {
+                        "blurb": "Currently selected path",
+                        "construct": false,
+                        "construct-only": false,
+                        "default": "-1",
+                        "max": "-1",
+                        "min": "0",
+                        "type-name": "guint",
+                        "writable": false
+                    },
+                    "message-forward": {
+                        "blurb": "Forwards all children messages",
+                        "construct": false,
+                        "construct-only": false,
+                        "default": "false",
+                        "type-name": "gboolean",
+                        "writable": true
+                    },
+                    "num-paths": {
+                        "blurb": "Number of paths",
+                        "construct": false,
+                        "construct-only": false,
+                        "default": "0",
+                        "max": "-2",
+                        "min": "0",
+                        "type-name": "guint",
+                        "writable": true
+                    }
+                },
+                "rank": "none"
+            }
+        },
+        "filename": "gstswitchbin",
+        "license": "LGPL",
+        "package": "GStreamer Bad Plug-ins git",
+        "source": "gst-plugins-bad",
+        "tracers": {},
+        "url": "Unknown package origin"
+    },
     "teletext": {
         "description": "Teletext plugin",
         "elements": {

gst/switchbin/gstswitchbin.c

@@ -19,6 +19,44 @@
  * Boston, MA 02110-1301, USA.
  */
 
+/**
+ * SECTION:element-switchbin
+ * @title: switchbin
+ *
+ * switchbin is a helper element which chooses between a set of
+ * processing chains (paths) based on input caps, and changes if new caps
+ * arrive. Paths are child objects, which are accessed by the
+ * #GstChildProxy interface.
+ *
+ * Whenever new input caps are encountered at the switchbin's sinkpad,
+ * the * first path with matching caps is picked. The paths are looked at
+ * in order: path \#0's caps are looked at first, checked against the new
+ * input caps with gst_caps_can_intersect(), and if its return value
+ * is TRUE, path \#0 is picked. Otherwise, path \#1's caps are looked at etc.
+ * If no path matches, an error is reported.
+ *
+ * <refsect2>
+ * <title>Example launch line</title>
+ *
+ * In this example, if the data is raw PCM audio with 44.1 kHz, a volume
+ * element is used for reducing the audio volume to 10%. Otherwise, it is
+ * just passed through. So, a 44.1 kHz MP3 will sound quiet, a 48 kHz MP3
+ * will be at full volume.
+ *
+ * |[
+ *   gst-launch-1.0 uridecodebin uri=<URI> ! switchbin num-paths=2 \
+ *     path0::element="audioconvert ! volume volume=0.1" path0::caps="audio/x-raw, rate=44100" \
+ *     path1::element="identity" path1::caps="ANY" ! \
+ *     autoaudiosink
+ * ]|
+ *
+ * This example's path \#1 is a fallback "catch-all" path. Its caps are "ANY" caps,
+ * so any input caps will match against this. A catch-all path with an identity element
+ * is useful for cases where certain kinds of processing should only be done for specific
+ * formats, like the example above (it applies volume only to 44.1 kHz PCM audio).
+ * </refsect2>
+ *
+ */
 
 #include <string.h>
 #include <stdio.h>
@@ -39,17 +77,14 @@ enum
   PROP_NUM_PATHS
 };
 
-
 #define DEFAULT_NUM_PATHS 0
 
-
 static GstStaticPadTemplate static_sink_template =
 GST_STATIC_PAD_TEMPLATE ("sink",
     GST_PAD_SINK,
     GST_PAD_ALWAYS,
     GST_STATIC_CAPS_ANY);
 
-
 static GstStaticPadTemplate static_src_template =
 GST_STATIC_PAD_TEMPLATE ("src",
     GST_PAD_SRC,
@@ -178,6 +213,14 @@ gst_switch_bin_class_init (GstSwitchBinClass * klass)
   object_class->set_property = GST_DEBUG_FUNCPTR (gst_switch_bin_set_property);
   object_class->get_property = GST_DEBUG_FUNCPTR (gst_switch_bin_get_property);
 
+  /**
+   * GstSwitchBin:num-paths
+   *
+   * Configure how many paths the switchbin will be choosing between. Attempting
+   * to configure a path outside the range 0..(n-1) will fail. Reducing the
+   * number of paths will release any paths outside the new range, which might
+   * trigger activation of a new path by re-assessing the current caps.
+   */
   g_object_class_install_property (object_class,
       PROP_NUM_PATHS,
       g_param_spec_uint ("num-paths",