gst/autoconvert/gstautoconvert.c

/* GStreamer
 *
 *  Copyright 2007-2012 Collabora Ltd
 *   @author: Olivier Crete <olivier.crete@collabora.com>
 *  Copyright 2007-2008 Nokia
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */
/**
 * SECTION:element-autoconvert
 * @title: autoconvert
 *
 * The #autoconvert element has one sink and one source pad. It will look for
 * other elements that also have one sink and one source pad.
 * It will then pick an element that matches the caps on both sides.
 * If the caps change, it may change the selected element if the current one
 * no longer matches the caps.
 *
 * The list of element it will look into can be specified in the
 * #GstAutoConvert::factories property, otherwise it will look at all available
 * elements.
 */


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "gstautoconvert.h"

#include <string.h>

GST_DEBUG_CATEGORY (autoconvert_debug);
#define GST_CAT_DEFAULT (autoconvert_debug)

#define GST_AUTOCONVERT_LOCK(ac) GST_OBJECT_LOCK (ac)
#define GST_AUTOCONVERT_UNLOCK(ac) GST_OBJECT_UNLOCK (ac)

/* elementfactory information */
static GstStaticPadTemplate sinktemplate = GST_STATIC_PAD_TEMPLATE ("sink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS_ANY);

static GstStaticPadTemplate srctemplate = GST_STATIC_PAD_TEMPLATE ("src",
    GST_PAD_SRC,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS_ANY);

static GstStaticPadTemplate sink_internal_template =
GST_STATIC_PAD_TEMPLATE ("sink_internal",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS_ANY);

static GstStaticPadTemplate src_internal_template =
GST_STATIC_PAD_TEMPLATE ("src_internal",
    GST_PAD_SRC,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS_ANY);

/* GstAutoConvert signals and args */
enum
{
  /* FILL ME */
  LAST_SIGNAL
};

enum
{
  PROP_0,
  PROP_FACTORIES
};

static void gst_auto_convert_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec);
static void gst_auto_convert_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec);
static void gst_auto_convert_dispose (GObject * object);

static GstElement *gst_auto_convert_get_subelement (GstAutoConvert *
    autoconvert);
static GstPad *gst_auto_convert_get_internal_sinkpad (GstAutoConvert *
    autoconvert);
static GstPad *gst_auto_convert_get_internal_srcpad (GstAutoConvert *
    autoconvert);

static GstIterator *gst_auto_convert_iterate_internal_links (GstPad * pad,
    GstObject * parent);

static gboolean gst_auto_convert_sink_setcaps (GstAutoConvert * autoconvert,
    GstCaps * caps);
static GstCaps *gst_auto_convert_getcaps (GstAutoConvert * autoconvert,
    GstCaps * filter, GstPadDirection dir);
static GstFlowReturn gst_auto_convert_sink_chain (GstPad * pad,
    GstObject * parent, GstBuffer * buffer);
static GstFlowReturn gst_auto_convert_sink_chain_list (GstPad * pad,
    GstObject * parent, GstBufferList * list);
static gboolean gst_auto_convert_sink_event (GstPad * pad, GstObject * parent,
    GstEvent * event);
static gboolean gst_auto_convert_sink_query (GstPad * pad, GstObject * parent,
    GstQuery * query);

static gboolean gst_auto_convert_src_event (GstPad * pad, GstObject * parent,
    GstEvent * event);
static gboolean gst_auto_convert_src_query (GstPad * pad, GstObject * parent,
    GstQuery * query);

static GstFlowReturn gst_auto_convert_internal_sink_chain (GstPad * pad,
    GstObject * parent, GstBuffer * buffer);
static GstFlowReturn gst_auto_convert_internal_sink_chain_list (GstPad * pad,
    GstObject * parent, GstBufferList * list);
static gboolean gst_auto_convert_internal_sink_event (GstPad * pad,
    GstObject * parent, GstEvent * event);
static gboolean gst_auto_convert_internal_sink_query (GstPad * pad,
    GstObject * parent, GstQuery * query);

static gboolean gst_auto_convert_internal_src_event (GstPad * pad,
    GstObject * parent, GstEvent * event);
static gboolean gst_auto_convert_internal_src_query (GstPad * pad,
    GstObject * parent, GstQuery * query);

static GList *gst_auto_convert_load_factories (GstAutoConvert * autoconvert);
static GstElement
    * gst_auto_convert_get_or_make_element_from_factory (GstAutoConvert *
    autoconvert, GstElementFactory * factory);
static gboolean gst_auto_convert_activate_element (GstAutoConvert * autoconvert,
    GstElement * element, GstCaps * caps);

static GQuark internal_srcpad_quark = 0;
static GQuark internal_sinkpad_quark = 0;
static GQuark parent_quark = 0;

G_DEFINE_TYPE (GstAutoConvert, gst_auto_convert, GST_TYPE_BIN);

static void
gst_auto_convert_class_init (GstAutoConvertClass * klass)
{
  GObjectClass *gobject_class = (GObjectClass *) klass;
  GstElementClass *gstelement_class = (GstElementClass *) klass;

  GST_DEBUG_CATEGORY_INIT (autoconvert_debug, "autoconvert", 0,
      "Auto convert based on caps");

  internal_srcpad_quark = g_quark_from_static_string ("internal_srcpad");
  internal_sinkpad_quark = g_quark_from_static_string ("internal_sinkpad");
  parent_quark = g_quark_from_static_string ("parent");


  gst_element_class_add_static_pad_template (gstelement_class, &srctemplate);
  gst_element_class_add_static_pad_template (gstelement_class, &sinktemplate);

  gst_element_class_set_static_metadata (gstelement_class,
      "Select convertor based on caps", "Generic/Bin",
      "Selects the right transform element based on the caps",
      "Olivier Crete <olivier.crete@collabora.com>");

  gobject_class->dispose = GST_DEBUG_FUNCPTR (gst_auto_convert_dispose);

  gobject_class->set_property = gst_auto_convert_set_property;
  gobject_class->get_property = gst_auto_convert_get_property;

  g_object_class_install_property (gobject_class, PROP_FACTORIES,
      g_param_spec_pointer ("factories",
          "GList of GstElementFactory",
          "GList of GstElementFactory objects to pick from (the element takes"
          " ownership of the list (NULL means it will go through all possible"
          " elements), can only be set once",
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
}

static void
gst_auto_convert_init (GstAutoConvert * autoconvert)
{
  autoconvert->sinkpad =
      gst_pad_new_from_static_template (&sinktemplate, "sink");
  autoconvert->srcpad = gst_pad_new_from_static_template (&srctemplate, "src");

  gst_pad_set_chain_function (autoconvert->sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_sink_chain));
  gst_pad_set_chain_list_function (autoconvert->sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_sink_chain_list));
  gst_pad_set_event_function (autoconvert->sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_sink_event));
  gst_pad_set_query_function (autoconvert->sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_sink_query));
  gst_pad_set_iterate_internal_links_function (autoconvert->sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_iterate_internal_links));

  gst_pad_set_event_function (autoconvert->srcpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_src_event));
  gst_pad_set_query_function (autoconvert->srcpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_src_query));
  gst_pad_set_iterate_internal_links_function (autoconvert->sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_iterate_internal_links));

  gst_element_add_pad (GST_ELEMENT (autoconvert), autoconvert->sinkpad);
  gst_element_add_pad (GST_ELEMENT (autoconvert), autoconvert->srcpad);
}

static void
gst_auto_convert_dispose (GObject * object)
{
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (object);

  g_clear_object (&autoconvert->current_subelement);
  g_clear_object (&autoconvert->current_internal_sinkpad);
  g_clear_object (&autoconvert->current_internal_srcpad);

  for (;;) {
    GList *factories = g_atomic_pointer_get (&autoconvert->factories);

    if (g_atomic_pointer_compare_and_exchange (&autoconvert->factories,
            factories, NULL)) {
      gst_plugin_feature_list_free (factories);
      break;
    }
  }

  G_OBJECT_CLASS (gst_auto_convert_parent_class)->dispose (object);
}

static void
gst_auto_convert_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec)
{
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (object);

  switch (prop_id) {
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
    case PROP_FACTORIES:
      if (g_atomic_pointer_get (&autoconvert->factories) == NULL) {
        GList *factories = g_value_get_pointer (value);
        factories = g_list_copy (factories);
        if (g_atomic_pointer_compare_and_exchange (&autoconvert->factories,
                NULL, factories))
          g_list_foreach (factories, (GFunc) g_object_ref, NULL);
        else
          g_list_free (factories);
      } else {
        GST_WARNING_OBJECT (object, "Can not reset factories after they"
            " have been set or auto-discovered");
      }
      break;
  }
}

static void
gst_auto_convert_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec)
{
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (object);

  switch (prop_id) {
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
    case PROP_FACTORIES:
      g_value_set_pointer (value,
          g_atomic_pointer_get (&autoconvert->factories));
      break;
  }
}


static GstElement *
gst_auto_convert_get_element_by_type (GstAutoConvert * autoconvert, GType type)
{
  GList *item;
  GstBin *bin = GST_BIN (autoconvert);
  GstElement *element = NULL;

  g_return_val_if_fail (type != 0, NULL);

  GST_OBJECT_LOCK (autoconvert);

  for (item = bin->children; item; item = item->next) {
    if (G_TYPE_CHECK_INSTANCE_TYPE (item->data, type)) {
      element = gst_object_ref (item->data);
      break;
    }
  }

  GST_OBJECT_UNLOCK (autoconvert);

  return element;
}

/**
 * get_pad_by_direction:
 * @element: The Element
 * @direction: The direction
 *
 * Gets a #GstPad that goes in the requested direction. I will return NULL
 * if there is no pad or if there is more than one pad in this direction
 */

static GstPad *
get_pad_by_direction (GstElement * element, GstPadDirection direction)
{
  GstIterator *iter = gst_element_iterate_pads (element);
  GstPad *selected_pad = NULL;
  gboolean done;
  GValue item = { 0, };

  if (!iter)
    return NULL;

  done = FALSE;
  while (!done) {
    switch (gst_iterator_next (iter, &item)) {
      case GST_ITERATOR_OK:
      {
        GstPad *pad = g_value_get_object (&item);

        if (gst_pad_get_direction (pad) == direction) {
          /* We check if there is more than one pad in this direction,
           * if there is, we return NULL so that the element is refused
           */
          if (selected_pad) {
            done = TRUE;
            gst_object_unref (selected_pad);
            selected_pad = NULL;
          } else {
            selected_pad = g_object_ref (pad);
          }
        }
        g_value_unset (&item);
      }
        break;
      case GST_ITERATOR_RESYNC:
        if (selected_pad) {
          gst_object_unref (selected_pad);
          selected_pad = NULL;
        }
        gst_iterator_resync (iter);
        break;
      case GST_ITERATOR_ERROR:
        GST_ERROR ("Error iterating pads of element %s",
            GST_OBJECT_NAME (element));
        gst_object_unref (selected_pad);
        selected_pad = NULL;
        done = TRUE;
        break;
      case GST_ITERATOR_DONE:
        done = TRUE;
        break;
    }
  }
  g_value_unset (&item);
  gst_iterator_free (iter);

  if (!selected_pad)
    GST_ERROR ("Did not find pad of direction %d in %s",
        direction, GST_OBJECT_NAME (element));

  return selected_pad;
}

static GstElement *
gst_auto_convert_get_subelement (GstAutoConvert * autoconvert)
{
  GstElement *element = NULL;

  GST_AUTOCONVERT_LOCK (autoconvert);
  if (autoconvert->current_subelement)
    element = gst_object_ref (autoconvert->current_subelement);
  GST_AUTOCONVERT_UNLOCK (autoconvert);

  return element;
}

static GstPad *
gst_auto_convert_get_internal_sinkpad (GstAutoConvert * autoconvert)
{
  GstPad *pad = NULL;

  GST_AUTOCONVERT_LOCK (autoconvert);
  if (autoconvert->current_internal_sinkpad)
    pad = gst_object_ref (autoconvert->current_internal_sinkpad);
  GST_AUTOCONVERT_UNLOCK (autoconvert);

  return pad;
}

static GstPad *
gst_auto_convert_get_internal_srcpad (GstAutoConvert * autoconvert)
{
  GstPad *pad = NULL;

  GST_AUTOCONVERT_LOCK (autoconvert);
  if (autoconvert->current_internal_srcpad)
    pad = gst_object_ref (autoconvert->current_internal_srcpad);
  GST_AUTOCONVERT_UNLOCK (autoconvert);

  return pad;
}

/*
 * This function creates and adds an element to the GstAutoConvert
 * it then creates the internal pads and links them
 *
 */

static GstElement *
gst_auto_convert_add_element (GstAutoConvert * autoconvert,
    GstElementFactory * factory)
{
  GstElement *element = NULL;
  GstPad *internal_sinkpad = NULL;
  GstPad *internal_srcpad = NULL;
  GstPad *sinkpad = NULL;
  GstPad *srcpad = NULL;
  GstPadLinkReturn padlinkret;

  GST_DEBUG_OBJECT (autoconvert, "Adding element %s to the autoconvert bin",
      gst_plugin_feature_get_name (GST_PLUGIN_FEATURE (factory)));

  element = gst_element_factory_create (factory, NULL);
  if (!element)
    return NULL;

  if (!gst_bin_add (GST_BIN (autoconvert), element)) {
    GST_ERROR_OBJECT (autoconvert, "Could not add element %s to the bin",
        GST_OBJECT_NAME (element));
    gst_object_unref (element);
    return NULL;
  }

  srcpad = get_pad_by_direction (element, GST_PAD_SRC);
  if (!srcpad) {
    GST_ERROR_OBJECT (autoconvert, "Could not find source in %s",
        GST_OBJECT_NAME (element));
    goto error;
  }

  sinkpad = get_pad_by_direction (element, GST_PAD_SINK);
  if (!sinkpad) {
    GST_ERROR_OBJECT (autoconvert, "Could not find sink in %s",
        GST_OBJECT_NAME (element));
    goto error;
  }

  internal_sinkpad =
      gst_pad_new_from_static_template (&sink_internal_template,
      "sink_internal");
  internal_srcpad =
      gst_pad_new_from_static_template (&src_internal_template, "src_internal");

  if (!internal_sinkpad || !internal_srcpad) {
    GST_ERROR_OBJECT (autoconvert, "Could not create internal pads");
    if (internal_srcpad)
      gst_object_unref (internal_srcpad);
    if (internal_sinkpad)
      gst_object_unref (internal_sinkpad);
    goto error;
  }

  g_object_weak_ref (G_OBJECT (element), (GWeakNotify) gst_object_unref,
      internal_sinkpad);
  g_object_weak_ref (G_OBJECT (element), (GWeakNotify) gst_object_unref,
      internal_srcpad);

  gst_pad_set_active (internal_sinkpad, TRUE);
  gst_pad_set_active (internal_srcpad, TRUE);

  g_object_set_qdata (G_OBJECT (internal_srcpad), parent_quark, autoconvert);
  g_object_set_qdata (G_OBJECT (internal_sinkpad), parent_quark, autoconvert);

  gst_pad_set_chain_function (internal_sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_internal_sink_chain));
  gst_pad_set_chain_list_function (internal_sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_internal_sink_chain_list));
  gst_pad_set_event_function (internal_sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_internal_sink_event));
  gst_pad_set_query_function (internal_sinkpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_internal_sink_query));

  gst_pad_set_event_function (internal_srcpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_internal_src_event));
  gst_pad_set_query_function (internal_srcpad,
      GST_DEBUG_FUNCPTR (gst_auto_convert_internal_src_query));

  padlinkret = gst_pad_link_full (internal_srcpad, sinkpad,
      GST_PAD_LINK_CHECK_NOTHING);
  if (GST_PAD_LINK_FAILED (padlinkret)) {
    GST_WARNING_OBJECT (autoconvert, "Could not links pad %s:%s to %s:%s"
        " for reason %d",
        GST_DEBUG_PAD_NAME (internal_srcpad),
        GST_DEBUG_PAD_NAME (sinkpad), padlinkret);
    goto error;
  }

  padlinkret = gst_pad_link_full (srcpad, internal_sinkpad,
      GST_PAD_LINK_CHECK_NOTHING);
  if (GST_PAD_LINK_FAILED (padlinkret)) {
    GST_WARNING_OBJECT (autoconvert, "Could not links pad %s:%s to %s:%s"
        " for reason %d",
        GST_DEBUG_PAD_NAME (internal_srcpad),
        GST_DEBUG_PAD_NAME (sinkpad), padlinkret);
    goto error;
  }

  g_object_set_qdata (G_OBJECT (element),
      internal_srcpad_quark, internal_srcpad);
  g_object_set_qdata (G_OBJECT (element),
      internal_sinkpad_quark, internal_sinkpad);

  /* Iffy */
  gst_element_sync_state_with_parent (element);

  /* Increment the reference count we will return to the caller */
  gst_object_ref (element);

  /* unref sink and src pad */
  gst_object_unref (srcpad);
  gst_object_unref (sinkpad);
  return element;

error:
  gst_element_set_locked_state (element, TRUE);
  gst_element_set_state (element, GST_STATE_NULL);
  gst_bin_remove (GST_BIN (autoconvert), element);

  if (srcpad)
    gst_object_unref (srcpad);
  if (sinkpad)
    gst_object_unref (sinkpad);

  return NULL;
}

static GstElement *
gst_auto_convert_get_or_make_element_from_factory (GstAutoConvert * autoconvert,
    GstElementFactory * factory)
{
  GstElement *element = NULL;
  GstElementFactory *loaded_factory =
      GST_ELEMENT_FACTORY (gst_plugin_feature_load (GST_PLUGIN_FEATURE
          (factory)));

  if (!loaded_factory)
    return NULL;

  element = gst_auto_convert_get_element_by_type (autoconvert,
      gst_element_factory_get_element_type (loaded_factory));

  if (!element) {
    element = gst_auto_convert_add_element (autoconvert, loaded_factory);
  }

  gst_object_unref (loaded_factory);

  return element;
}

/*
 * This function checks if there is one and only one pad template on the
 * factory that can accept the given caps. If there is one and only one,
 * it returns TRUE, otherwise, its FALSE
 */

static gboolean
factory_can_intersect (GstAutoConvert * autoconvert,
    GstElementFactory * factory, GstPadDirection direction, GstCaps * caps)
{
  const GList *templates;
  gint has_direction = FALSE;
  gboolean ret = FALSE;

  g_return_val_if_fail (factory != NULL, FALSE);
  g_return_val_if_fail (caps != NULL, FALSE);

  templates = gst_element_factory_get_static_pad_templates (factory);

  while (templates) {
    GstStaticPadTemplate *template = (GstStaticPadTemplate *) templates->data;

    if (template->direction == direction) {
      GstCaps *tmpl_caps = NULL;
      gboolean intersect;

      /* If there is more than one pad in this direction, we return FALSE
       * Only transform elements (with one sink and one source pad)
       * are accepted
       */
      if (has_direction) {
        GST_DEBUG_OBJECT (autoconvert, "Factory %p"
            " has more than one static template with dir %d",
            template, direction);
        return FALSE;
      }
      has_direction = TRUE;

      tmpl_caps = gst_static_caps_get (&template->static_caps);
      intersect = gst_caps_can_intersect (tmpl_caps, caps);
      GST_DEBUG_OBJECT (autoconvert, "Factories %" GST_PTR_FORMAT
          " static caps %" GST_PTR_FORMAT " and caps %" GST_PTR_FORMAT
          " can%s intersect", factory, tmpl_caps, caps,
          intersect ? "" : " not");
      gst_caps_unref (tmpl_caps);

      ret |= intersect;
    }
    templates = g_list_next (templates);
  }

  return ret;
}

static gboolean
sticky_event_push (GstPad * pad, GstEvent ** event, gpointer user_data)
{
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (user_data);

  gst_event_ref (*event);
  gst_pad_push_event (autoconvert->current_internal_srcpad, *event);

  return TRUE;
}

static gboolean
gst_auto_convert_activate_element (GstAutoConvert * autoconvert,
    GstElement * element, GstCaps * caps)
{
  GstPad *internal_srcpad = g_object_get_qdata (G_OBJECT (element),
      internal_srcpad_quark);
  GstPad *internal_sinkpad = g_object_get_qdata (G_OBJECT (element),
      internal_sinkpad_quark);

  if (caps) {
    /* check if the element can really accept said caps */
    if (!gst_pad_peer_query_accept_caps (internal_srcpad, caps)) {
      GST_DEBUG_OBJECT (autoconvert, "Could not set %s:%s to %"
          GST_PTR_FORMAT, GST_DEBUG_PAD_NAME (internal_srcpad), caps);
      return FALSE;
    }
  }

  GST_AUTOCONVERT_LOCK (autoconvert);
  gst_object_replace ((GstObject **) & autoconvert->current_subelement,
      GST_OBJECT (element));
  gst_object_replace ((GstObject **) & autoconvert->current_internal_srcpad,
      GST_OBJECT (internal_srcpad));
  gst_object_replace ((GstObject **) & autoconvert->current_internal_sinkpad,
      GST_OBJECT (internal_sinkpad));
  GST_AUTOCONVERT_UNLOCK (autoconvert);

  gst_pad_sticky_events_foreach (autoconvert->sinkpad, sticky_event_push,
      autoconvert);

  gst_pad_push_event (autoconvert->sinkpad, gst_event_new_reconfigure ());

  GST_INFO_OBJECT (autoconvert, "Selected element %s",
      GST_OBJECT_NAME (GST_OBJECT (element)));

  gst_object_unref (element);

  return TRUE;
}

static GstIterator *
gst_auto_convert_iterate_internal_links (GstPad * pad, GstObject * parent)
{
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (parent);
  GstIterator *it = NULL;
  GstPad *internal;

  if (pad == autoconvert->sinkpad)
    internal = gst_auto_convert_get_internal_srcpad (autoconvert);
  else
    internal = gst_auto_convert_get_internal_sinkpad (autoconvert);

  if (internal) {
    GValue val = { 0, };

    g_value_init (&val, GST_TYPE_PAD);
    g_value_take_object (&val, internal);

    it = gst_iterator_new_single (GST_TYPE_PAD, &val);
    g_value_unset (&val);
  }

  return it;
}

/*
 * If there is already an internal element, it will try to call set_caps on it
 *
 * If there isn't an internal element or if the set_caps() on the internal
 * element failed, it will try to find another element where it would succeed
 * and will change the internal element.
 */

static gboolean
gst_auto_convert_sink_setcaps (GstAutoConvert * autoconvert, GstCaps * caps)
{
  GList *elem;
  GstCaps *other_caps = NULL;
  GList *factories;
  GstCaps *current_caps;

  g_return_val_if_fail (autoconvert != NULL, FALSE);

  current_caps = gst_pad_get_current_caps (autoconvert->sinkpad);
  if (current_caps) {
    if (gst_caps_is_equal_fixed (caps, current_caps)) {
      gst_caps_unref (current_caps);
      return TRUE;
    }
    gst_caps_unref (current_caps);
  }

  if (autoconvert->current_subelement) {
    if (gst_pad_peer_query_accept_caps (autoconvert->current_internal_srcpad,
            caps)) {
      /* If we can set the new caps on the current element,
       * then we just get out
       */
      GST_DEBUG_OBJECT (autoconvert, "Could set %s:%s to %" GST_PTR_FORMAT,
          GST_DEBUG_PAD_NAME (autoconvert->current_internal_srcpad), caps);
      goto get_out;
    } else {
      /* If the current element doesn't work,
       * then we remove the current element before finding a new one.
       */
      GST_AUTOCONVERT_LOCK (autoconvert);
      g_clear_object (&autoconvert->current_subelement);
      g_clear_object (&autoconvert->current_internal_sinkpad);
      g_clear_object (&autoconvert->current_internal_srcpad);
      GST_AUTOCONVERT_UNLOCK (autoconvert);
    }
  }

  other_caps = gst_pad_peer_query_caps (autoconvert->srcpad, NULL);

  factories = g_atomic_pointer_get (&autoconvert->factories);

  if (!factories)
    factories = gst_auto_convert_load_factories (autoconvert);

  for (elem = factories; elem; elem = g_list_next (elem)) {
    GstElementFactory *factory = GST_ELEMENT_FACTORY (elem->data);
    GstElement *element;

    /* Lets first check if according to the static pad templates on the factory
     * these caps have any chance of success
     */
    if (!factory_can_intersect (autoconvert, factory, GST_PAD_SINK, caps)) {
      GST_LOG_OBJECT (autoconvert, "Factory %s does not accept sink caps %"
          GST_PTR_FORMAT,
          gst_plugin_feature_get_name (GST_PLUGIN_FEATURE (factory)), caps);
      continue;
    }
    if (other_caps != NULL) {
      if (!factory_can_intersect (autoconvert, factory, GST_PAD_SRC,
              other_caps)) {
        GST_LOG_OBJECT (autoconvert,
            "Factory %s does not accept src caps %" GST_PTR_FORMAT,
            gst_plugin_feature_get_name (GST_PLUGIN_FEATURE (factory)),
            other_caps);
        continue;
      }
    }

    /* The element had a chance of success, lets make it */
    element =
        gst_auto_convert_get_or_make_element_from_factory (autoconvert,
        factory);
    if (!element)
      continue;

    /* And make it the current child */
    if (gst_auto_convert_activate_element (autoconvert, element, caps))
      break;
    else
      gst_object_unref (element);
  }

get_out:
  if (other_caps)
    gst_caps_unref (other_caps);

  if (autoconvert->current_subelement) {
    return TRUE;
  } else {
    GST_WARNING_OBJECT (autoconvert,
        "Could not find a matching element for caps");
    return FALSE;
  }
}

/*
 * This function filters the pad pad templates, taking only transform element
 * (with one sink and one src pad)
 */

static gboolean
gst_auto_convert_default_filter_func (GstPluginFeature * feature,
    gpointer user_data)
{
  GstElementFactory *factory = NULL;
  const GList *static_pad_templates, *tmp;
  GstStaticPadTemplate *src = NULL, *sink = NULL;

  if (!GST_IS_ELEMENT_FACTORY (feature))
    return FALSE;

  factory = GST_ELEMENT_FACTORY (feature);

  static_pad_templates = gst_element_factory_get_static_pad_templates (factory);

  for (tmp = static_pad_templates; tmp; tmp = g_list_next (tmp)) {
    GstStaticPadTemplate *template = tmp->data;
    GstCaps *caps;

    if (template->presence == GST_PAD_SOMETIMES)
      return FALSE;

    if (template->presence != GST_PAD_ALWAYS)
      continue;

    switch (template->direction) {
      case GST_PAD_SRC:
        if (src)
          return FALSE;
        src = template;
        break;
      case GST_PAD_SINK:
        if (sink)
          return FALSE;
        sink = template;
        break;
      default:
        return FALSE;
    }

    caps = gst_static_pad_template_get_caps (template);

    if (gst_caps_is_any (caps) || gst_caps_is_empty (caps))
      return FALSE;
  }

  if (!src || !sink)
    return FALSE;

  return TRUE;
}

/* function used to sort element features
 * Copy-pasted from decodebin */
static gint
compare_ranks (GstPluginFeature * f1, GstPluginFeature * f2)
{
  gint diff;
  const gchar *rname1, *rname2;

  diff = gst_plugin_feature_get_rank (f2) - gst_plugin_feature_get_rank (f1);
  if (diff != 0)
    return diff;

  rname1 = gst_plugin_feature_get_name (f1);
  rname2 = gst_plugin_feature_get_name (f2);

  diff = strcmp (rname2, rname1);

  return diff;
}

static GList *
gst_auto_convert_load_factories (GstAutoConvert * autoconvert)
{
  GList *all_factories;

  all_factories =
      gst_registry_feature_filter (gst_registry_get (),
      gst_auto_convert_default_filter_func, FALSE, NULL);

  all_factories = g_list_sort (all_factories, (GCompareFunc) compare_ranks);

  g_assert (all_factories);

  if (g_atomic_pointer_compare_and_exchange (&autoconvert->factories, NULL,
          all_factories)) {
    gst_plugin_feature_list_free (all_factories);
  }

  return g_atomic_pointer_get (&autoconvert->factories);
}

/* In this case, we should almost always have an internal element, because
 * set_caps() should have been called first
 */

static GstFlowReturn
gst_auto_convert_sink_chain (GstPad * pad, GstObject * parent,
    GstBuffer * buffer)
{
  GstFlowReturn ret = GST_FLOW_NOT_NEGOTIATED;
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (parent);

  if (autoconvert->current_internal_srcpad) {
    ret = gst_pad_push (autoconvert->current_internal_srcpad, buffer);
    if (ret != GST_FLOW_OK)
      GST_DEBUG_OBJECT (autoconvert,
          "Child element %" GST_PTR_FORMAT "returned flow %s",
          autoconvert->current_subelement, gst_flow_get_name (ret));
  } else {
    GST_ERROR_OBJECT (autoconvert, "Got buffer without an negotiated element,"
        " returning not-negotiated");
    gst_buffer_unref (buffer);
  }

  return ret;
}

static GstFlowReturn
gst_auto_convert_sink_chain_list (GstPad * pad, GstObject * parent,
    GstBufferList * list)
{
  GstFlowReturn ret = GST_FLOW_NOT_NEGOTIATED;
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (parent);

  if (autoconvert->current_internal_srcpad) {
    ret = gst_pad_push_list (autoconvert->current_internal_srcpad, list);
    if (ret != GST_FLOW_OK)
      GST_DEBUG_OBJECT (autoconvert,
          "Child element %" GST_PTR_FORMAT "returned flow %s",
          autoconvert->current_subelement, gst_flow_get_name (ret));
  } else {
    GST_ERROR_OBJECT (autoconvert, "Got buffer without an negotiated element,"
        " returning not-negotiated");
    gst_buffer_list_unref (list);
  }

  return ret;
}

static gboolean
gst_auto_convert_sink_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
  gboolean ret = TRUE;
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (parent);
  GstPad *internal_srcpad;

  if (GST_EVENT_TYPE (event) == GST_EVENT_CAPS) {
    GstCaps *caps;

    gst_event_parse_caps (event, &caps);
    ret = gst_auto_convert_sink_setcaps (autoconvert, caps);
    if (!ret) {
      gst_event_unref (event);
      return ret;
    }
  }

  internal_srcpad = gst_auto_convert_get_internal_srcpad (autoconvert);
  if (internal_srcpad) {
    ret = gst_pad_push_event (internal_srcpad, event);
    gst_object_unref (internal_srcpad);
  } else {
    switch (GST_EVENT_TYPE (event)) {
      case GST_EVENT_FLUSH_STOP:
      case GST_EVENT_FLUSH_START:
        ret = gst_pad_push_event (autoconvert->srcpad, event);
        break;
      default:
        gst_event_unref (event);
        ret = TRUE;
        break;
    }
  }

  return ret;
}

/* TODO Properly test that this code works well for queries */
static gboolean
gst_auto_convert_sink_query (GstPad * pad, GstObject * parent, GstQuery * query)
{
  gboolean ret = TRUE;
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (parent);
  GstElement *subelement;

  if (GST_QUERY_TYPE (query) == GST_QUERY_CAPS) {
    GstCaps *filter, *caps;

    gst_query_parse_caps (query, &filter);
    caps = gst_auto_convert_getcaps (autoconvert, filter, GST_PAD_SINK);
    gst_query_set_caps_result (query, caps);
    gst_caps_unref (caps);

    return TRUE;
  }

  subelement = gst_auto_convert_get_subelement (autoconvert);
  if (subelement) {
    GstPad *sub_sinkpad = get_pad_by_direction (subelement, GST_PAD_SINK);

    ret = gst_pad_query (sub_sinkpad, query);

    gst_object_unref (sub_sinkpad);
    gst_object_unref (subelement);

    if (ret && GST_QUERY_TYPE (query) == GST_QUERY_ACCEPT_CAPS) {
      gboolean res;
      gst_query_parse_accept_caps_result (query, &res);

      if (!res)
        goto ignore_acceptcaps_failure;
    }
    return ret;
  }

ignore_acceptcaps_failure:

  if (GST_QUERY_TYPE (query) == GST_QUERY_ACCEPT_CAPS) {
    GstCaps *caps;
    GstCaps *accept_caps;

    gst_query_parse_accept_caps (query, &accept_caps);

    caps = gst_auto_convert_getcaps (autoconvert, accept_caps, GST_PAD_SINK);
    gst_query_set_accept_caps_result (query,
        gst_caps_can_intersect (caps, accept_caps));
    gst_caps_unref (caps);

    return TRUE;
  }

  GST_WARNING_OBJECT (autoconvert, "Got query %s while no element was"
      " selected, letting through",
      gst_query_type_get_name (GST_QUERY_TYPE (query)));
  return gst_pad_peer_query (autoconvert->srcpad, query);
}

/**
 * gst_auto_convert_getcaps:
 * @pad: the sink #GstPad
 *
 * This function returns the union of the caps of all the possible element
 * factories, based on the static pad templates.
 * It also checks does a getcaps on the downstream element and ignores all
 * factories whose static caps can not satisfy it.
 *
 * It does not try to use each elements getcaps() function
 */

static GstCaps *
gst_auto_convert_getcaps (GstAutoConvert * autoconvert, GstCaps * filter,
    GstPadDirection dir)
{
  GstCaps *caps = NULL, *other_caps = NULL;
  GList *elem, *factories;

  caps = gst_caps_new_empty ();

  if (dir == GST_PAD_SINK)
    other_caps = gst_pad_peer_query_caps (autoconvert->srcpad, NULL);
  else
    other_caps = gst_pad_peer_query_caps (autoconvert->sinkpad, NULL);

  GST_DEBUG_OBJECT (autoconvert,
      "Lets find all the element that can fit here with src caps %"
      GST_PTR_FORMAT, other_caps);

  if (other_caps && gst_caps_is_empty (other_caps)) {
    goto out;
  }

  factories = g_atomic_pointer_get (&autoconvert->factories);

  if (!factories)
    factories = gst_auto_convert_load_factories (autoconvert);

  for (elem = factories; elem; elem = g_list_next (elem)) {
    GstElementFactory *factory = GST_ELEMENT_FACTORY (elem->data);
    GstElement *element = NULL;
    GstCaps *element_caps;
    GstPad *internal_pad = NULL;

    if (filter) {
      if (!factory_can_intersect (autoconvert, factory, dir, filter)) {
        GST_LOG_OBJECT (autoconvert,
            "Factory %s does not accept src caps %" GST_PTR_FORMAT,
            gst_plugin_feature_get_name (GST_PLUGIN_FEATURE (factory)),
            other_caps);
        continue;
      }
    }

    if (other_caps != NULL) {
      if (!factory_can_intersect (autoconvert, factory,
              dir == GST_PAD_SINK ? GST_PAD_SRC : GST_PAD_SINK, other_caps)) {
        GST_LOG_OBJECT (autoconvert,
            "Factory %s does not accept src caps %" GST_PTR_FORMAT,
            gst_plugin_feature_get_name (GST_PLUGIN_FEATURE (factory)),
            other_caps);
        continue;
      }

      element = gst_auto_convert_get_or_make_element_from_factory (autoconvert,
          factory);
      if (element == NULL)
        continue;

      if (dir == GST_PAD_SINK)
        internal_pad = g_object_get_qdata (G_OBJECT (element),
            internal_srcpad_quark);
      else
        internal_pad = g_object_get_qdata (G_OBJECT (element),
            internal_sinkpad_quark);

      element_caps = gst_pad_peer_query_caps (internal_pad, filter);

      if (element_caps)
        caps = gst_caps_merge (caps, element_caps);

      gst_object_unref (element);

      /* Early out, any is absorbing */
      if (gst_caps_is_any (caps))
        goto out;
    } else {
      const GList *tmp;

      for (tmp = gst_element_factory_get_static_pad_templates (factory);
          tmp; tmp = g_list_next (tmp)) {
        GstStaticPadTemplate *template = tmp->data;

        if (GST_PAD_TEMPLATE_DIRECTION (template) == dir) {
          GstCaps *static_caps = gst_static_pad_template_get_caps (template);

          if (static_caps) {
            caps = gst_caps_merge (caps, static_caps);
          }

          /* Early out, any is absorbing */
          if (gst_caps_is_any (caps))
            goto out;
        }
      }
    }
  }

  GST_DEBUG_OBJECT (autoconvert, "Returning unioned caps %" GST_PTR_FORMAT,
      caps);

out:

  if (other_caps)
    gst_caps_unref (other_caps);

  return caps;
}



static gboolean
gst_auto_convert_src_event (GstPad * pad, GstObject * parent, GstEvent * event)
{
  gboolean ret = TRUE;
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (parent);
  GstPad *internal_sinkpad;

  if (GST_EVENT_TYPE (event) == GST_EVENT_RECONFIGURE)
    gst_pad_push_event (autoconvert->sinkpad, gst_event_ref (event));

  internal_sinkpad = gst_auto_convert_get_internal_sinkpad (autoconvert);
  if (internal_sinkpad) {
    ret = gst_pad_push_event (internal_sinkpad, event);
    gst_object_unref (internal_sinkpad);
  } else if (GST_EVENT_TYPE (event) != GST_EVENT_RECONFIGURE) {
    GST_WARNING_OBJECT (autoconvert,
        "Got upstream event while no element was selected," "forwarding.");
    ret = gst_pad_push_event (autoconvert->sinkpad, event);
  } else
    gst_event_unref (event);

  return ret;
}

/* TODO Properly test that this code works well for queries */
static gboolean
gst_auto_convert_src_query (GstPad * pad, GstObject * parent, GstQuery * query)
{
  gboolean ret = TRUE;
  GstAutoConvert *autoconvert = GST_AUTO_CONVERT (parent);
  GstElement *subelement;

  if (GST_QUERY_TYPE (query) == GST_QUERY_CAPS) {
    GstCaps *filter, *caps;

    gst_query_parse_caps (query, &filter);
    caps = gst_auto_convert_getcaps (autoconvert, filter, GST_PAD_SRC);
    gst_query_set_caps_result (query, caps);
    gst_caps_unref (caps);

    return TRUE;
  }

  subelement = gst_auto_convert_get_subelement (autoconvert);
  if (subelement) {
    GstPad *sub_srcpad = get_pad_by_direction (subelement, GST_PAD_SRC);

    ret = gst_pad_query (sub_srcpad, query);

    gst_object_unref (sub_srcpad);
    gst_object_unref (subelement);
  } else {
    GST_WARNING_OBJECT (autoconvert,
        "Got upstream query of type %s while no element was selected,"
        " forwarding.", gst_query_type_get_name (GST_QUERY_TYPE (query)));
    ret = gst_pad_peer_query (autoconvert->sinkpad, query);
  }

  return ret;
}

static GstFlowReturn
gst_auto_convert_internal_sink_chain (GstPad * pad, GstObject * parent,
    GstBuffer * buffer)
{
  GstAutoConvert *autoconvert =
      GST_AUTO_CONVERT (g_object_get_qdata (G_OBJECT (pad),
          parent_quark));

  return gst_pad_push (autoconvert->srcpad, buffer);
}

static GstFlowReturn
gst_auto_convert_internal_sink_chain_list (GstPad * pad, GstObject * parent,
    GstBufferList * list)
{
  GstAutoConvert *autoconvert =
      GST_AUTO_CONVERT (g_object_get_qdata (G_OBJECT (pad),
          parent_quark));

  return gst_pad_push_list (autoconvert->srcpad, list);
}

static gboolean
gst_auto_convert_internal_sink_event (GstPad * pad, GstObject * parent,
    GstEvent * event)
{
  GstAutoConvert *autoconvert =
      GST_AUTO_CONVERT (g_object_get_qdata (G_OBJECT (pad),
          parent_quark));
  gboolean drop = FALSE;

  GST_AUTOCONVERT_LOCK (autoconvert);
  if (autoconvert->current_internal_sinkpad != pad) {
    drop = TRUE;
  }
  GST_AUTOCONVERT_UNLOCK (autoconvert);

  if (drop) {
    gst_event_unref (event);
    return TRUE;
  }

  return gst_pad_push_event (autoconvert->srcpad, event);
}

static gboolean
gst_auto_convert_internal_sink_query (GstPad * pad, GstObject * parent,
    GstQuery * query)
{
  GstAutoConvert *autoconvert =
      GST_AUTO_CONVERT (g_object_get_qdata (G_OBJECT (pad),
          parent_quark));

  if (!gst_pad_peer_query (autoconvert->srcpad, query)) {
    switch (GST_QUERY_TYPE (query)) {
      case GST_QUERY_CAPS:
      {
        GstCaps *filter;

        gst_query_parse_caps (query, &filter);
        if (filter) {
          gst_query_set_caps_result (query, filter);
        } else {
          filter = gst_caps_new_any ();
          gst_query_set_caps_result (query, filter);
          gst_caps_unref (filter);
        }
        return TRUE;
      }
      case GST_QUERY_ACCEPT_CAPS:
        gst_query_set_accept_caps_result (query, TRUE);
        return TRUE;
      default:
        return FALSE;
    }
  }

  return TRUE;
}

static gboolean
gst_auto_convert_internal_src_event (GstPad * pad, GstObject * parent,
    GstEvent * event)
{
  GstAutoConvert *autoconvert =
      GST_AUTO_CONVERT (g_object_get_qdata (G_OBJECT (pad),
          parent_quark));
  gboolean drop = FALSE;

  GST_AUTOCONVERT_LOCK (autoconvert);
  if (autoconvert->current_internal_srcpad != pad) {
    drop = TRUE;
  }
  GST_AUTOCONVERT_UNLOCK (autoconvert);

  if (drop) {
    GST_DEBUG_OBJECT (autoconvert, "Dropping event %" GST_PTR_FORMAT, event);
    gst_event_unref (event);
    return TRUE;
  }

  return gst_pad_push_event (autoconvert->sinkpad, event);
}

static gboolean
gst_auto_convert_internal_src_query (GstPad * pad, GstObject * parent,
    GstQuery * query)
{
  GstAutoConvert *autoconvert =
      GST_AUTO_CONVERT (g_object_get_qdata (G_OBJECT (pad),
          parent_quark));

  return gst_pad_peer_query (autoconvert->sinkpad, query);
}