diff -r 9b2c3c7a1a9c -r 567bb019e3e3 gstreamer_core/gst/gstpreset.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gstreamer_core/gst/gstpreset.c	Tue Aug 31 15:30:33 2010 +0300
@@ -0,0 +1,1153 @@
+/* GStreamer
+ * Copyright (C) 2006 Stefan Kost <ensonic@users.sf.net>
+ *
+ * gstpreset.c: helper interface for element presets
+ *
+ * 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., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+/**
+ * SECTION:gstpreset
+ * @short_description: helper interface for element presets
+ *
+ * This interface offers methods to query and manipulate parameter preset sets.
+ * A preset is a bunch of property settings, together with meta data and a name.
+ * The name of a preset serves as key for subsequent method calls to manipulate
+ * single presets.
+ * All instances of one type will share the list of presets. The list is created
+ * on demand, if presets are not used, the list is not created.
+ *
+ * The interface comes with a default implementation that serves most plugins.
+ * Wrapper plugins will override most methods to implement support for the
+ * native preset format of those wrapped plugins.
+ * One method that is useful to be overridden is gst_preset_get_property_names().
+ * With that one can control which properties are saved and in which order.
+ */
+/* FIXME:
+ * - non racyness
+ *   - we need to avoid two instances writing the preset file
+ *     -> flock(fileno()), http://www.ecst.csuchico.edu/~beej/guide/ipc/flock.html
+ *     -> open exclusive
+ *     -> better save the new file to a tempfile and then rename?
+ *   - we like to know when any other instance makes changes to the keyfile
+ *     - then ui can be updated
+ *     - and we make sure that we don't lose edits
+ *   -> its the same problem actually, once for inside a process, once system-
+ *      wide
+ *     - can we use a lock inside a names shared memory segment?
+ *
+ * - need to add support for GstChildProxy
+ *   we can do this in a next iteration, the format is flexible enough
+ *   http://www.buzztard.org/index.php/Preset_handling_interface
+ *
+ * - should there be a 'preset-list' property to get the preset list
+ *   (and to connect a notify:: to to listen for changes)
+ *   we could use gnome_vfs_monitor_add() to monitor the user preset_file.
+ *
+ * - should there be a 'preset-name' property so that we can set a preset via
+ *   gst-launch, or should we handle this with special syntax in gst-launch:
+ *   gst-launch element preset:<preset-name> property=value ...
+ *   - this would alloow to hanve preset-bundles too (a preset on bins that
+ *     specifies presets for children
+ *
+ * - GstChildProxy suport
+ *   - if we stick with GParamSpec **_list_properties()
+ *     we need to use g_param_spec_set_qdata() to specify the instance on each GParamSpec
+ *     OBJECT_LOCK(obj);  // ChildProxy needs GstIterator support
+ *     num=gst_child_proxy_get_children_count(obj);
+ *     for(i=0;i<num;i++) {
+ *       child=gst_child_proxy_get_child_by_index(obj,i);
+ *       // v1 ----
+ *       g_object_class_list_properties(child,&num);
+ *       // foreach prop
+ *       //   g_param_spec_set_qdata(prop, quark, (gpointer)child);
+ *       //   add to result
+ *       // v2 ----
+ *       // children have to implement preset-iface too tag the returned GParamSpec* with the owner
+ *       props=gst_preset_list_properties(child);
+ *       // add props to result
+ *     }
+ *     OBJECT_UNLOCK(obj);
+ *
+ */
+
+#include "gst_private.h"
+
+#include "gstpreset.h"
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#include <glib/gstdio.h>
+
+#define GST_CAT_DEFAULT preset_debug
+GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
+
+/* defines for keyfile usage, this group contains the element type name and
+ * version these presets belong to. */
+#define PRESET_HEADER "_presets_"
+
+/* keys of the preset header section */
+#define PRESET_HEADER_ELEMENT_NAME "element-name"
+#define PRESET_HEADER_VERSION "version"
+
+static GQuark preset_user_path_quark = 0;
+static GQuark preset_system_path_quark = 0;
+static GQuark preset_quark = 0;
+
+/*static GQuark property_list_quark = 0;*/
+
+/* default iface implementation */
+
+static gboolean gst_preset_default_save_presets_file (GstPreset * preset);
+
+/*
+ * preset_get_paths:
+ * @preset: a #GObject that implements #GstPreset
+ * @preset_user_path: location for path or %NULL
+ * @preset_system_path: location for path or %NULL
+ *
+ * Fetch the preset_path for user local and system wide settings. Don't free
+ * after use.
+ *
+ * Returns: %FALSE if no paths could be found.
+ */
+static gboolean
+preset_get_paths (GstPreset * preset, const gchar ** preset_user_path,
+    const gchar ** preset_system_path)
+{
+  GType type = G_TYPE_FROM_INSTANCE (preset);
+  gchar *preset_path;
+  const gchar *element_name;
+
+  /* we use the element name when we must contruct the paths */
+  element_name = G_OBJECT_TYPE_NAME (preset);
+  GST_INFO_OBJECT (preset, "element_name: '%s'", element_name);
+
+  if (preset_user_path) {
+    /* preset user path requested, see if we have it cached in the qdata */
+    if (!(preset_path = g_type_get_qdata (type, preset_user_path_quark))) {
+      gchar *preset_dir;
+
+      /* user presets go in '$HOME/.gstreamer-0.10/presets/GstSimSyn.prs' */
+      preset_dir = g_build_filename (g_get_home_dir (),
+          ".gstreamer-" GST_MAJORMINOR, "presets", NULL);
+      GST_INFO_OBJECT (preset, "user_preset_dir: '%s'", preset_dir);
+      preset_path =
+          g_strdup_printf ("%s" G_DIR_SEPARATOR_S "%s.prs", preset_dir,
+          element_name);
+      GST_INFO_OBJECT (preset, "user_preset_path: '%s'", preset_path);
+      /* create dirs */
+      g_mkdir_with_parents (preset_dir, 0755);
+      g_free (preset_dir);
+
+      /* cache the preset path to the type */
+      g_type_set_qdata (type, preset_user_path_quark, preset_path);
+    }
+    *preset_user_path = preset_path;
+  }
+
+  if (preset_system_path) {
+    /* preset system path requested, see if we have it cached in the qdata */
+    if (!(preset_path = g_type_get_qdata (type, preset_system_path_quark))) {
+      gchar *preset_dir;
+
+      /* system presets in '$GST_DATADIR/gstreamer-0.10/presets/GstAudioPanorama.prs' */
+      preset_dir = g_build_filename (GST_DATADIR, "gstreamer-" GST_MAJORMINOR,
+          "presets", NULL);
+      GST_INFO_OBJECT (preset, "system_preset_dir: '%s'", preset_dir);
+      preset_path = g_strdup_printf ("%s" G_DIR_SEPARATOR_S "%s.prs",
+          preset_dir, element_name);
+      GST_INFO_OBJECT (preset, "system_preset_path: '%s'", preset_path);
+      /* create dirs */
+      g_mkdir_with_parents (preset_dir, 0755);
+      g_free (preset_dir);
+
+      /* cache the preset path to the type */
+      g_type_set_qdata (type, preset_system_path_quark, preset_path);
+    }
+    *preset_system_path = preset_path;
+  }
+  return TRUE;
+}
+
+static gboolean
+preset_skip_property (GParamSpec * property)
+{
+  if (((property->flags & G_PARAM_READWRITE) != G_PARAM_READWRITE) ||
+      (property->flags & G_PARAM_CONSTRUCT_ONLY))
+    return TRUE;
+  /* FIXME: skip GST_PARAM_NOT_PRESETABLE, see #522205 */
+  return FALSE;
+}
+
+/* caller must free @preset_version after use */
+static GKeyFile *
+preset_open_and_parse_header (GstPreset * preset, const gchar * preset_path,
+    gchar ** preset_version)
+{
+  GKeyFile *in;
+  GError *error = NULL;
+  gboolean res;
+  const gchar *element_name;
+  gchar *name;
+
+  in = g_key_file_new ();
+
+  res = g_key_file_load_from_file (in, preset_path,
+      G_KEY_FILE_KEEP_COMMENTS | G_KEY_FILE_KEEP_TRANSLATIONS, &error);
+  if (!res || error != NULL)
+    goto load_error;
+
+  /* element type name and preset name must match or we are dealing with a wrong
+   * preset file */
+  element_name = G_OBJECT_TYPE_NAME (preset);
+  name =
+      g_key_file_get_value (in, PRESET_HEADER, PRESET_HEADER_ELEMENT_NAME,
+      NULL);
+
+  if (!name || strcmp (name, element_name))
+    goto wrong_name;
+
+  g_free (name);
+
+  /* get the version now so that the caller can check it */
+  if (preset_version)
+    *preset_version =
+        g_key_file_get_value (in, PRESET_HEADER, PRESET_HEADER_VERSION, NULL);
+
+  return in;
+
+  /* ERRORS */
+load_error:
+  {
+    GST_WARNING_OBJECT (preset, "Unable to read preset file %s: %s",
+        preset_path, error->message);
+    g_error_free (error);
+    g_key_file_free (in);
+    return NULL;
+  }
+wrong_name:
+  {
+    GST_WARNING_OBJECT (preset,
+        "Wrong element name in preset file %s. Expected %s, got %s",
+        preset_path, element_name, GST_STR_NULL (name));
+    g_free (name);
+    g_key_file_free (in);
+    return NULL;
+  }
+}
+
+static guint64
+preset_parse_version (const gchar * str_version)
+{
+  gint major, minor, micro, nano, num;
+
+  major = minor = micro = nano = 0;
+
+  /* parse version (e.g. 0.10.15.1) to guint64 */
+  num = sscanf (str_version, "%d.%d.%d.%d", &major, &minor, &micro, &nano);
+  /* make sure we have atleast "major.minor" */
+  if (num > 1) {
+    guint64 version;
+
+    version = ((((major << 8 | minor) << 8) | micro) << 8) | nano;
+    GST_DEBUG ("version %s -> %" G_GUINT64_FORMAT, str_version, version);
+    return version;
+  }
+  return G_GUINT64_CONSTANT (0);
+}
+
+static void
+preset_merge (GKeyFile * system, GKeyFile * user)
+{
+  gchar *str;
+  gchar **groups, **keys;
+  gsize i, j, num_groups, num_keys;
+
+  /* copy file comment if there is any */
+  if ((str = g_key_file_get_comment (user, NULL, NULL, NULL))) {
+    g_key_file_set_comment (system, NULL, NULL, str, NULL);
+    g_free (str);
+  }
+
+  /* get groups in user and copy into system */
+  groups = g_key_file_get_groups (user, &num_groups);
+  for (i = 0; i < num_groups; i++) {
+    /* copy group comment if there is any */
+    if ((str = g_key_file_get_comment (user, groups[i], NULL, NULL))) {
+      g_key_file_set_comment (system, groups[i], NULL, str, NULL);
+      g_free (str);
+    }
+
+    /* ignore private groups */
+    if (groups[i][0] == '_')
+      continue;
+
+    /* if group already exists in system, remove and re-add keys from user */
+    if (g_key_file_has_group (system, groups[i])) {
+      g_key_file_remove_group (system, groups[i], NULL);
+    }
+
+    keys = g_key_file_get_keys (user, groups[i], &num_keys, NULL);
+    for (j = 0; j < num_keys; j++) {
+      /* copy key comment if there is any */
+      if ((str = g_key_file_get_comment (user, groups[i], keys[j], NULL))) {
+        g_key_file_set_comment (system, groups[i], keys[j], str, NULL);
+        g_free (str);
+      }
+      str = g_key_file_get_value (user, groups[i], keys[j], NULL);
+      g_key_file_set_value (system, groups[i], keys[j], str);
+      g_free (str);
+    }
+    g_strfreev (keys);
+  }
+  g_strfreev (groups);
+}
+
+/* reads the user and system presets files and merges them together. This
+ * function caches the GKeyFile on the element type. If there is no existing
+ * preset file, a new in-memory GKeyFile will be created. */
+static GKeyFile *
+preset_get_keyfile (GstPreset * preset)
+{
+  GKeyFile *presets;
+  GType type = G_TYPE_FROM_INSTANCE (preset);
+
+  /* first see if the have a cached version for the type */
+  if (!(presets = g_type_get_qdata (type, preset_quark))) {
+    const gchar *preset_user_path, *preset_system_path;
+    gchar *str_version_user = NULL, *str_version_system = NULL;
+    gboolean updated_from_system = FALSE;
+    GKeyFile *in_user, *in_system;
+
+    preset_get_paths (preset, &preset_user_path, &preset_system_path);
+
+    /* try to load the user and system presets, we do this to get the versions
+     * of both files. */
+    in_user = preset_open_and_parse_header (preset, preset_user_path,
+        &str_version_user);
+    in_system = preset_open_and_parse_header (preset, preset_system_path,
+        &str_version_system);
+
+    /* compare version to check for merge */
+    if (in_system) {
+      /* keep system presets if there is no user preset or when the system
+       * version is higher than the user version. */
+      if (!in_user) {
+        presets = in_system;
+      } else if (preset_parse_version (str_version_system) >
+          preset_parse_version (str_version_user)) {
+        presets = in_system;
+        updated_from_system = TRUE;
+      }
+    }
+    if (in_user) {
+      if (updated_from_system) {
+        /* merge user on top of system presets */
+        preset_merge (presets, in_user);
+        g_key_file_free (in_user);
+      } else {
+        /* keep user presets */
+        presets = in_user;
+      }
+    }
+    if (!in_user && !in_system) {
+      /* we did not load a user or system presets file, create a new one */
+      presets = g_key_file_new ();
+      g_key_file_set_string (presets, PRESET_HEADER, PRESET_HEADER_ELEMENT_NAME,
+          G_OBJECT_TYPE_NAME (preset));
+    }
+
+    g_free (str_version_user);
+    g_free (str_version_system);
+
+    /* attach the preset to the type */
+    g_type_set_qdata (type, preset_quark, (gpointer) presets);
+
+    if (updated_from_system) {
+      gst_preset_default_save_presets_file (preset);
+    }
+  }
+  return presets;
+}
+
+/* get a list of all supported preset names for an element */
+static gchar **
+gst_preset_default_get_preset_names (GstPreset * preset)
+{
+  GKeyFile *presets;
+  gsize i, num_groups;
+  gchar **groups;
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  /* get the groups, which are also the preset names */
+  if (!(groups = g_key_file_get_groups (presets, &num_groups)))
+    goto no_groups;
+
+  /* remove all private group names starting with '_' from the array */
+  for (i = 0; i < num_groups; i++) {
+    if (groups[i][0] == '_') {
+      /* free private group */
+      g_free (groups[i]);
+      /* move last element of list down */
+      num_groups--;
+      /* move last element into removed element */
+      groups[i] = groups[num_groups];
+      groups[num_groups] = NULL;
+    }
+  }
+  /* sort the array now */
+  g_qsort_with_data (groups, num_groups, sizeof (gchar *),
+      (GCompareDataFunc) strcmp, NULL);
+
+  return groups;
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset, "Could not load presets");
+    return NULL;
+  }
+no_groups:
+  {
+    GST_WARNING_OBJECT (preset, "Could not find preset groups");
+    return NULL;
+  }
+}
+
+/* get a list of all property names that are used for presets */
+static gchar **
+gst_preset_default_get_property_names (GstPreset * preset)
+{
+  GParamSpec **props;
+  guint i, j, n_props;
+  GObjectClass *gclass;
+  gchar **result;
+
+  gclass = G_OBJECT_CLASS (GST_ELEMENT_GET_CLASS (preset));
+
+  /* get a list of normal properties. 
+   * FIXME, change this for childproxy support. */
+  props = g_object_class_list_properties (gclass, &n_props);
+  if (!props)
+    goto no_properties;
+
+  /* allocate array big enough to hold the worst case, including a terminating
+   * NULL pointer. */
+  result = g_new (gchar *, n_props + 1);
+
+  /* now filter out the properties that we can use for presets */
+  GST_DEBUG_OBJECT (preset, "  filtering properties: %u", n_props);
+  for (i = j = 0; i < n_props; i++) {
+    if (preset_skip_property (props[i]))
+      continue;
+
+    /* copy and increment out pointer */
+    result[j++] = g_strdup (props[i]->name);
+  }
+  result[j] = NULL;
+  g_free (props);
+
+  return result;
+
+  /* ERRORS */
+no_properties:
+  {
+    GST_INFO_OBJECT (preset, "object has no properties");
+    return NULL;
+  }
+}
+
+/* load the presets of @name for the instance @preset. Returns %FALSE if something
+ * failed. */
+static gboolean
+gst_preset_default_load_preset (GstPreset * preset, const gchar * name)
+{
+  GKeyFile *presets;
+  gchar **props;
+  guint i;
+  GObjectClass *gclass;
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  /* get the preset name */
+  if (!g_key_file_has_group (presets, name))
+    goto no_group;
+
+  GST_DEBUG_OBJECT (preset, "loading preset : '%s'", name);
+
+  /* get the properties that we can configure in this element */
+  if (!(props = gst_preset_get_property_names (preset)))
+    goto no_properties;
+
+  gclass = G_OBJECT_CLASS (GST_ELEMENT_GET_CLASS (preset));
+
+  /* for each of the property names, find the preset parameter and try to
+   * configure the property with its value */
+  for (i = 0; props[i]; i++) {
+    gchar *str;
+    GValue gvalue = { 0, };
+    GParamSpec *property;
+
+    /* check if we have a settings for this element property */
+    if (!(str = g_key_file_get_value (presets, name, props[i], NULL))) {
+      /* the element has a property but the parameter is not in the keyfile */
+      GST_WARNING_OBJECT (preset, "parameter '%s' not in preset", props[i]);
+      continue;
+    }
+
+    GST_DEBUG_OBJECT (preset, "setting value '%s' for property '%s'", str,
+        props[i]);
+
+    /* FIXME, change for childproxy to get the property and element.  */
+    if (!(property = g_object_class_find_property (gclass, props[i]))) {
+      /* the parameter was in the keyfile, the element said it supported it but
+       * then the property was not found in the element. This should not happen. */
+      GST_WARNING_OBJECT (preset, "property '%s' not in object", props[i]);
+      g_free (str);
+      continue;
+    }
+
+    /* try to deserialize the property value from the keyfile and set it as
+     * the object property */
+    g_value_init (&gvalue, property->value_type);
+    if (gst_value_deserialize (&gvalue, str)) {
+      /* FIXME, change for childproxy support */
+      g_object_set_property (G_OBJECT (preset), props[i], &gvalue);
+    } else {
+      GST_WARNING_OBJECT (preset,
+          "deserialization of value '%s' for property '%s' failed", str,
+          props[i]);
+    }
+    g_value_unset (&gvalue);
+    g_free (str);
+  }
+  g_strfreev (props);
+
+  return TRUE;
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset, "no presets");
+    return FALSE;
+  }
+no_group:
+  {
+    GST_WARNING_OBJECT (preset, "no preset named '%s'", name);
+    return FALSE;
+  }
+no_properties:
+  {
+    GST_INFO_OBJECT (preset, "no properties");
+    return FALSE;
+  }
+}
+
+/* save the presets file. A copy of the existing presets file is stored in a
+ * .bak file */
+static gboolean
+gst_preset_default_save_presets_file (GstPreset * preset)
+{
+  GKeyFile *presets;
+  const gchar *preset_path;
+  GError *error = NULL;
+  gchar *bak_file_name;
+  gboolean backup = TRUE;
+  gchar *data;
+  gsize data_size;
+
+  preset_get_paths (preset, &preset_path, NULL);
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  GST_DEBUG_OBJECT (preset, "saving preset file: '%s'", preset_path);
+
+  /* create backup if possible */
+  bak_file_name = g_strdup_printf ("%s.bak", preset_path);
+  if (g_file_test (bak_file_name, G_FILE_TEST_EXISTS)) {
+    if (g_unlink (bak_file_name)) {
+      backup = FALSE;
+      GST_INFO_OBJECT (preset, "cannot remove old backup file : %s",
+          bak_file_name);
+    }
+  }
+  if (backup) {
+    if (g_rename (preset_path, bak_file_name)) {
+      GST_INFO_OBJECT (preset, "cannot backup file : %s -> %s", preset_path,
+          bak_file_name);
+    }
+  }
+  g_free (bak_file_name);
+
+  /* update gstreamer version */
+  g_key_file_set_string (presets, PRESET_HEADER, PRESET_HEADER_VERSION,
+      PACKAGE_VERSION);
+
+  /* get new contents, wee need this to save it */
+  if (!(data = g_key_file_to_data (presets, &data_size, &error)))
+    goto convert_failed;
+
+  /* write presets */
+  if (!g_file_set_contents (preset_path, data, data_size, &error))
+    goto write_failed;
+
+  g_free (data);
+
+  return TRUE;
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset,
+        "no presets, trying to unlink possibly existing preset file: '%s'",
+        preset_path);
+    g_unlink (preset_path);
+    return FALSE;
+  }
+convert_failed:
+  {
+    GST_WARNING_OBJECT (preset, "can not get the keyfile contents: %s",
+        error->message);
+    g_error_free (error);
+    g_free (data);
+    return FALSE;
+  }
+write_failed:
+  {
+    GST_WARNING_OBJECT (preset, "Unable to store preset file %s: %s",
+        preset_path, error->message);
+    g_error_free (error);
+    g_free (data);
+    return FALSE;
+  }
+}
+
+/* save the preset with the given name */
+static gboolean
+gst_preset_default_save_preset (GstPreset * preset, const gchar * name)
+{
+  GKeyFile *presets;
+  gchar **props;
+  guint i;
+  GObjectClass *gclass;
+
+  GST_INFO_OBJECT (preset, "saving new preset: %s", name);
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  /* take copies of current gobject properties from preset */
+  if (!(props = gst_preset_get_property_names (preset)))
+    goto no_properties;
+
+  gclass = G_OBJECT_CLASS (GST_ELEMENT_GET_CLASS (preset));
+
+  /* loop over the object properties and store the property value in the
+   * keyfile */
+  for (i = 0; props[i]; i++) {
+    GValue gvalue = { 0, };
+    gchar *str;
+    GParamSpec *property;
+
+    /* FIXME, change for childproxy to get the property and element.  */
+    if (!(property = g_object_class_find_property (gclass, props[i]))) {
+      /* the element said it supported the property but then it does not have
+       * that property. This should not happen. */
+      GST_WARNING_OBJECT (preset, "property '%s' not in object", props[i]);
+      continue;
+    }
+
+    g_value_init (&gvalue, property->value_type);
+    /* FIXME, change for childproxy */
+    g_object_get_property (G_OBJECT (preset), props[i], &gvalue);
+
+    if ((str = gst_value_serialize (&gvalue))) {
+      g_key_file_set_string (presets, name, props[i], (gpointer) str);
+      g_free (str);
+    } else {
+      GST_WARNING_OBJECT (preset, "serialization for property '%s' failed",
+          props[i]);
+    }
+    g_value_unset (&gvalue);
+  }
+  GST_INFO_OBJECT (preset, "  saved");
+  g_strfreev (props);
+
+  /* save updated version */
+  return gst_preset_default_save_presets_file (preset);
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset, "no presets");
+    return FALSE;
+  }
+no_properties:
+  {
+    GST_INFO_OBJECT (preset, "no properties");
+    return FALSE;
+  }
+}
+
+/* copies all keys and comments from one group to another, deleting the old
+ * group. */
+static gboolean
+gst_preset_default_rename_preset (GstPreset * preset, const gchar * old_name,
+    const gchar * new_name)
+{
+  GKeyFile *presets;
+  gchar *str;
+  gchar **keys;
+  gsize i, num_keys;
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  if (!g_key_file_has_group (presets, old_name))
+    goto no_group;
+
+  /* copy group comment if there is any */
+  if ((str = g_key_file_get_comment (presets, old_name, NULL, NULL))) {
+    g_key_file_set_comment (presets, new_name, NULL, str, NULL);
+    g_free (str);
+  }
+
+  /* get all keys from the old group and copy them in the new group */
+  keys = g_key_file_get_keys (presets, old_name, &num_keys, NULL);
+  for (i = 0; i < num_keys; i++) {
+    /* copy key comment if there is any */
+    if ((str = g_key_file_get_comment (presets, old_name, keys[i], NULL))) {
+      g_key_file_set_comment (presets, new_name, keys[i], str, NULL);
+      g_free (str);
+    }
+    /* copy key value */
+    str = g_key_file_get_value (presets, old_name, keys[i], NULL);
+    g_key_file_set_value (presets, new_name, keys[i], str);
+    g_free (str);
+  }
+  g_strfreev (keys);
+
+  /* remove old group */
+  g_key_file_remove_group (presets, old_name, NULL);
+
+  /* save updated version */
+  return gst_preset_default_save_presets_file (preset);
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset, "no presets");
+    return FALSE;
+  }
+no_group:
+  {
+    GST_WARNING_OBJECT (preset, "no preset named %s", old_name);
+    return FALSE;
+  }
+}
+
+/* delete a group from the keyfile */
+static gboolean
+gst_preset_default_delete_preset (GstPreset * preset, const gchar * name)
+{
+  GKeyFile *presets;
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  /* get the group */
+  if (!g_key_file_has_group (presets, name))
+    goto no_group;
+
+  /* remove the group */
+  g_key_file_remove_group (presets, name, NULL);
+
+  /* save updated version */
+  return gst_preset_default_save_presets_file (preset);
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset, "no presets");
+    return FALSE;
+  }
+no_group:
+  {
+    GST_WARNING_OBJECT (preset, "no preset named %s", name);
+    return FALSE;
+  }
+}
+
+static gboolean
+gst_preset_default_set_meta (GstPreset * preset, const gchar * name,
+    const gchar * tag, const gchar * value)
+{
+  GKeyFile *presets;
+  gchar *key;
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  key = g_strdup_printf ("_meta/%s", tag);
+  if (value && *value) {
+    g_key_file_set_value (presets, name, key, value);
+  } else {
+    g_key_file_remove_key (presets, name, key, NULL);
+  }
+  g_free (key);
+
+  /* save updated keyfile */
+  return gst_preset_default_save_presets_file (preset);
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset, "no presets");
+    return FALSE;
+  }
+}
+
+/* the caller must free @value after usage */
+static gboolean
+gst_preset_default_get_meta (GstPreset * preset, const gchar * name,
+    const gchar * tag, gchar ** value)
+{
+  GKeyFile *presets;
+  gchar *key;
+
+  /* get the presets from the type */
+  if (!(presets = preset_get_keyfile (preset)))
+    goto no_presets;
+
+  key = g_strdup_printf ("_meta/%s", tag);
+  *value = g_key_file_get_value (presets, name, key, NULL);
+  g_free (key);
+
+  return TRUE;
+
+  /* ERRORS */
+no_presets:
+  {
+    GST_WARNING_OBJECT (preset, "no presets");
+    *value = NULL;
+    return FALSE;
+  }
+}
+
+/* wrapper */
+
+/**
+ * gst_preset_get_preset_names:
+ * @preset: a #GObject that implements #GstPreset
+ *
+ * Get a copy of preset names as a NULL terminated string array.
+ *
+ * Returns: list with names, ue g_strfreev() after usage.
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gchar **
+gst_preset_get_preset_names (GstPreset * preset)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), NULL);
+
+  return (GST_PRESET_GET_INTERFACE (preset)->get_preset_names (preset));
+}
+
+/**
+ * gst_preset_get_property_names:
+ * @preset: a #GObject that implements #GstPreset
+ *
+ * Get a the names of the GObject properties that can be used for presets.
+ *
+ * Returns: an array of property names which should be freed with g_strfreev() after use.
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gchar **
+gst_preset_get_property_names (GstPreset * preset)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), NULL);
+
+  return (GST_PRESET_GET_INTERFACE (preset)->get_property_names (preset));
+}
+
+/**
+ * gst_preset_load_preset:
+ * @preset: a #GObject that implements #GstPreset
+ * @name: preset name to load
+ *
+ * Load the given preset.
+ *
+ * Returns: %TRUE for success, %FALSE if e.g. there is no preset with that @name
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gboolean
+gst_preset_load_preset (GstPreset * preset, const gchar * name)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), FALSE);
+  g_return_val_if_fail (name, FALSE);
+
+  return (GST_PRESET_GET_INTERFACE (preset)->load_preset (preset, name));
+}
+
+/**
+ * gst_preset_save_preset:
+ * @preset: a #GObject that implements #GstPreset
+ * @name: preset name to save
+ *
+ * Save the current preset under the given name. If there is already a preset by
+ * this @name it will be overwritten.
+ *
+ * Returns: %TRUE for success, %FALSE
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gboolean
+gst_preset_save_preset (GstPreset * preset, const gchar * name)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), FALSE);
+  g_return_val_if_fail (name, FALSE);
+
+  return (GST_PRESET_GET_INTERFACE (preset)->save_preset (preset, name));
+}
+
+/**
+ * gst_preset_rename_preset:
+ * @preset: a #GObject that implements #GstPreset
+ * @old_name: current preset name
+ * @new_name: new preset name
+ *
+ * Renames a preset. If there is already a preset by the @new_name it will be
+ * overwritten.
+ *
+ * Returns: %TRUE for success, %FALSE if e.g. there is no preset with @old_name
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gboolean
+gst_preset_rename_preset (GstPreset * preset, const gchar * old_name,
+    const gchar * new_name)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), FALSE);
+  g_return_val_if_fail (old_name, FALSE);
+  g_return_val_if_fail (new_name, FALSE);
+
+  return (GST_PRESET_GET_INTERFACE (preset)->rename_preset (preset, old_name,
+          new_name));
+}
+
+/**
+ * gst_preset_delete_preset:
+ * @preset: a #GObject that implements #GstPreset
+ * @name: preset name to remove
+ *
+ * Delete the given preset.
+ *
+ * Returns: %TRUE for success, %FALSE if e.g. there is no preset with that @name
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gboolean
+gst_preset_delete_preset (GstPreset * preset, const gchar * name)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), FALSE);
+  g_return_val_if_fail (name, FALSE);
+
+  return (GST_PRESET_GET_INTERFACE (preset)->delete_preset (preset, name));
+}
+
+/**
+ * gst_preset_set_meta:
+ * @preset: a #GObject that implements #GstPreset
+ * @name: preset name
+ * @tag: meta data item name
+ * @value: new value
+ *
+ * Sets a new @value for an existing meta data item or adds a new item. Meta
+ * data @tag names can be something like e.g. "comment". Supplying %NULL for the
+ * @value will unset an existing value.
+ *
+ * Returns: %TRUE for success, %FALSE if e.g. there is no preset with that @name
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gboolean
+gst_preset_set_meta (GstPreset * preset, const gchar * name, const gchar * tag,
+    const gchar * value)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), FALSE);
+  g_return_val_if_fail (name, FALSE);
+  g_return_val_if_fail (tag, FALSE);
+
+  return GST_PRESET_GET_INTERFACE (preset)->set_meta (preset, name, tag, value);
+}
+
+/**
+ * gst_preset_get_meta:
+ * @preset: a #GObject that implements #GstPreset
+ * @name: preset name
+ * @tag: meta data item name
+ * @value: value
+ *
+ * Gets the @value for an existing meta data @tag. Meta data @tag names can be
+ * something like e.g. "comment". Returned values need to be released when done.
+ *
+ * Returns: %TRUE for success, %FALSE if e.g. there is no preset with that @name
+ * or no value for the given @tag
+ *
+ * Since: 0.10.20
+ */
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+gboolean
+gst_preset_get_meta (GstPreset * preset, const gchar * name, const gchar * tag,
+    gchar ** value)
+{
+  g_return_val_if_fail (GST_IS_PRESET (preset), FALSE);
+  g_return_val_if_fail (name, FALSE);
+  g_return_val_if_fail (tag, FALSE);
+  g_return_val_if_fail (value, FALSE);
+
+  return GST_PRESET_GET_INTERFACE (preset)->get_meta (preset, name, tag, value);
+}
+
+/* class internals */
+
+static void
+gst_preset_class_init (GstPresetInterface * iface)
+{
+  iface->get_preset_names = gst_preset_default_get_preset_names;
+  iface->get_property_names = gst_preset_default_get_property_names;
+
+  iface->load_preset = gst_preset_default_load_preset;
+  iface->save_preset = gst_preset_default_save_preset;
+  iface->rename_preset = gst_preset_default_rename_preset;
+  iface->delete_preset = gst_preset_default_delete_preset;
+
+  iface->set_meta = gst_preset_default_set_meta;
+  iface->get_meta = gst_preset_default_get_meta;
+}
+
+static void
+gst_preset_base_init (gpointer g_class)
+{
+  static gboolean initialized = FALSE;
+
+  if (!initialized) {
+    /* init default implementation */
+    GST_DEBUG_CATEGORY_INIT (GST_CAT_DEFAULT, "preset",
+        GST_DEBUG_FG_WHITE | GST_DEBUG_BG_BLACK, "preset interface");
+
+    /* create quarks for use with g_type_{g,s}et_qdata() */
+    preset_quark = g_quark_from_static_string ("GstPreset::presets");
+    preset_user_path_quark =
+        g_quark_from_static_string ("GstPreset::user_path");
+    preset_system_path_quark =
+        g_quark_from_static_string ("GstPreset::system_path");
+
+#if 0
+    property_list_quark = g_quark_from_static_string ("GstPreset::properties");
+
+    /* create interface properties, each element would need to override this
+     *   g_object_class_override_property(gobject_class, PROP_PRESET_NAME, "preset-name");
+     * and in _set_property() do
+     *   case PROP_PRESET_NAME: {
+     *     gchar *name = g_value_get_string (value);
+     *     if (name)
+     *       gst_preset_load_preset(preset, name);
+     *   } break;
+     */
+    g_object_interface_install_property (g_class,
+        g_param_spec_string ("preset-name",
+            "preset-name property",
+            "load given preset", NULL, G_PARAM_WRITABLE));
+#endif
+
+    initialized = TRUE;
+  }
+}
+#ifdef __SYMBIAN32__
+EXPORT_C
+#endif
+
+
+GType
+gst_preset_get_type (void)
+{
+  static volatile gsize type = 0;
+
+  if (g_once_init_enter (&type)) {
+    GType _type;
+    const GTypeInfo info = {
+      sizeof (GstPresetInterface),
+      (GBaseInitFunc) gst_preset_base_init,     /* base_init */
+      NULL,                     /* base_finalize */
+      (GClassInitFunc) gst_preset_class_init,   /* class_init */
+      NULL,                     /* class_finalize */
+      NULL,                     /* class_data */
+      0,
+      0,                        /* n_preallocs */
+      NULL                      /* instance_init */
+    };
+    _type = g_type_register_static (G_TYPE_INTERFACE, "GstPreset", &info, 0);
+    g_once_init_leave (&type, _type);
+  }
+  return type;
+}