gstevent.c 40.7 KB
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/* GStreamer
 * Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
 *                    2000 Wim Taymans <wim.taymans@chello.be>
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 *                    2005 Wim Taymans <wim@fluendo.com>
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 *
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 * gstevent.c: GstEvent subsystem
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 *
 * 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.
 */
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/**
 * SECTION:gstevent
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 * @short_description: Structure describing events that are passed up and down
 *                     a pipeline
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 * @see_also: #GstPad, #GstElement
 *
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 * The event class provides factory methods to construct events for sending
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 * and functions to query (parse) received events.
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 *
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 * Events are usually created with gst_event_new_*() which takes event-type
 * specific parameters as arguments.
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 * To send an event application will usually use gst_element_send_event() and
 * elements will use gst_pad_send_event() or gst_pad_push_event().
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 * The event should be unreffed with gst_event_unref() if it has not been sent.
 *
 * Events that have been received can be parsed with their respective 
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 * gst_event_parse_*() functions. It is valid to pass %NULL for unwanted details.
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 *
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 * Events are passed between elements in parallel to the data stream. Some events
 * are serialized with buffers, others are not. Some events only travel downstream,
 * others only upstream. Some events can travel both upstream and downstream. 
 * 
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 * The events are used to signal special conditions in the datastream such as
 * EOS (end of stream) or the start of a new stream-segment.
 * Events are also used to flush the pipeline of any pending data.
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 *
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 * Most of the event API is used inside plugins. Applications usually only 
 * construct and use seek events. 
 * To do that gst_event_new_seek() is used to create a seek event. It takes
 * the needed parameters to specity seeking time and mode.
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 * <example>
 * <title>performing a seek on a pipeline</title>
 *   <programlisting>
 *   GstEvent *event;
 *   gboolean result;
 *   ...
 *   // construct a seek event to play the media from second 2 to 5, flush
 *   // the pipeline to decrease latency.
 *   event = gst_event_new_seek (1.0, 
 *      GST_FORMAT_TIME, 
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 *      GST_SEEK_FLAG_FLUSH,
 *      GST_SEEK_TYPE_SET, 2 * GST_SECOND,
 *      GST_SEEK_TYPE_SET, 5 * GST_SECOND);
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 *   ...
 *   result = gst_element_send_event (pipeline, event);
 *   if (!result)
 *     g_warning ("seek failed");
 *   ...
 *   </programlisting>
 * </example>
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 *
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 * Last reviewed on 2006-09-6 (0.10.10)
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 */
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#include "gst_private.h"
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#include <string.h>             /* memcpy */
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#include "gstinfo.h"
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#include "gstevent.h"
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#include "gstenumtypes.h"
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#include "gstutils.h"
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#include "gstquark.h"
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GType _gst_event_type = 0;
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typedef struct
{
  GstQOSType type;
  gdouble proportion;
  gint64 diff;
  GstClockTime timestamp;
} GstEventQOSData;

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typedef struct
{
  GstEvent event;

  GstStructure *structure;
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  union
  {
    GstEventQOSData qos;
  };
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} GstEventImpl;

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#define GST_EVENT_STRUCTURE(e)        (((GstEventImpl *)(e))->structure)
#define GST_EVENT_IMPL(e,data,field)  (((GstEventImpl *)(e))->data.field)
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typedef struct
{
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  const gint type;
  const gchar *name;
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  GQuark quark;
} GstEventQuarks;

static GstEventQuarks event_quarks[] = {
  {GST_EVENT_UNKNOWN, "unknown", 0},
  {GST_EVENT_FLUSH_START, "flush-start", 0},
  {GST_EVENT_FLUSH_STOP, "flush-stop", 0},
  {GST_EVENT_EOS, "eos", 0},
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  {GST_EVENT_CAPS, "caps", 0},
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  {GST_EVENT_NEWSEGMENT, "newsegment", 0},
  {GST_EVENT_TAG, "tag", 0},
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  {GST_EVENT_BUFFERSIZE, "buffersize", 0},
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  {GST_EVENT_SINK_MESSAGE, "sink-message", 0},
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  {GST_EVENT_QOS, "qos", 0},
  {GST_EVENT_SEEK, "seek", 0},
  {GST_EVENT_NAVIGATION, "navigation", 0},
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  {GST_EVENT_LATENCY, "latency", 0},
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  {GST_EVENT_STEP, "step", 0},
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  {GST_EVENT_RECONFIGURE, "reconfigure", 0},
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  {GST_EVENT_CUSTOM_UPSTREAM, "custom-upstream", 0},
  {GST_EVENT_CUSTOM_DOWNSTREAM, "custom-downstream", 0},
  {GST_EVENT_CUSTOM_DOWNSTREAM_OOB, "custom-downstream-oob", 0},
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  {GST_EVENT_CUSTOM_BOTH, "custom-both", 0},
  {GST_EVENT_CUSTOM_BOTH_OOB, "custom-both-oob", 0},

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  {0, NULL, 0}
};

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void
_gst_event_initialize (void)
{
  gint i;
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  _gst_event_type = gst_mini_object_register ("GstEvent");

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  g_type_class_ref (gst_seek_flags_get_type ());
  g_type_class_ref (gst_seek_type_get_type ());

  for (i = 0; event_quarks[i].name; i++) {
    event_quarks[i].quark = g_quark_from_static_string (event_quarks[i].name);
  }
}

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/**
 * gst_event_type_get_name:
 * @type: the event type
 *
 * Get a printable name for the given event type. Do not modify or free.
 *
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 * Returns: a reference to the static name of the event.
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 */
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const gchar *
gst_event_type_get_name (GstEventType type)
{
  gint i;

  for (i = 0; event_quarks[i].name; i++) {
    if (type == event_quarks[i].type)
      return event_quarks[i].name;
  }
  return "unknown";
}

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/**
 * gst_event_type_to_quark:
 * @type: the event type
 *
 * Get the unique quark for the given event type.
 *
 * Returns: the quark associated with the event type
 */
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GQuark
gst_event_type_to_quark (GstEventType type)
{
  gint i;

  for (i = 0; event_quarks[i].name; i++) {
    if (type == event_quarks[i].type)
      return event_quarks[i].quark;
  }
  return 0;
}

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/**
 * gst_event_type_get_flags:
 * @type: a #GstEventType
 *
 * Gets the #GstEventTypeFlags associated with @type.
 *
 * Returns: a #GstEventTypeFlags.
 */
GstEventTypeFlags
gst_event_type_get_flags (GstEventType type)
{
  GstEventTypeFlags ret;

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  ret = type & ((1 << GST_EVENT_STICKY_SHIFT) - 1);
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  return ret;
}

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static void
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_gst_event_free (GstEvent * event)
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{
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  GstStructure *s;

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  g_return_if_fail (event != NULL);
  g_return_if_fail (GST_IS_EVENT (event));

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  GST_CAT_LOG (GST_CAT_EVENT, "freeing event %p type %s", event,
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      GST_EVENT_TYPE_NAME (event));
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  s = GST_EVENT_STRUCTURE (event);

  if (s) {
    gst_structure_set_parent_refcount (s, NULL);
    gst_structure_free (s);
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  }
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  g_slice_free1 (GST_MINI_OBJECT_SIZE (event), event);
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}

static GstEvent *
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_gst_event_copy (GstEventImpl * event)
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{
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  GstEventImpl *copy;
  GstStructure *s;
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  copy = g_slice_dup (GstEventImpl, event);
  gst_mini_object_init (GST_MINI_OBJECT_CAST (copy), _gst_event_type,
      sizeof (GstEventImpl));
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  GST_EVENT_TYPE (copy) = GST_EVENT_TYPE (event);
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  GST_EVENT_TIMESTAMP (copy) = GST_EVENT_TIMESTAMP (event);
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  GST_EVENT_SEQNUM (copy) = GST_EVENT_SEQNUM (event);
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  s = GST_EVENT_STRUCTURE (event);
  if (s) {
    GST_EVENT_STRUCTURE (copy) = gst_structure_copy (s);
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    gst_structure_set_parent_refcount (GST_EVENT_STRUCTURE (copy),
        &copy->event.mini_object.refcount);
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  }
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  return GST_EVENT_CAST (copy);
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}

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static void
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gst_event_init (GstEventImpl * event, gsize size, GstEventType type)
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{
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  gst_mini_object_init (GST_MINI_OBJECT_CAST (event), _gst_event_type, size);
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  event->event.mini_object.copy = (GstMiniObjectCopyFunction) _gst_event_copy;
  event->event.mini_object.free = (GstMiniObjectFreeFunction) _gst_event_free;
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  GST_EVENT_TYPE (event) = type;
  GST_EVENT_TIMESTAMP (event) = GST_CLOCK_TIME_NONE;
  GST_EVENT_SEQNUM (event) = gst_util_seqnum_next ();
}

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static GstEvent *
gst_event_new (GstEventType type)
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{
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  GstEventImpl *event;
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  event = g_slice_new0 (GstEventImpl);
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  GST_CAT_DEBUG (GST_CAT_EVENT, "creating new event %p %s %d", event,
      gst_event_type_get_name (type), type);
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  gst_event_init (event, sizeof (GstEventImpl), type);
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  return GST_EVENT_CAST (event);
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}

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/**
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 * gst_event_new_custom:
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 * @type: The type of the new event
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 * @structure: (transfer full): the structure for the event. The event will
 *     take ownership of the structure.
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 *
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 * Create a new custom-typed event. This can be used for anything not
 * handled by other event-specific functions to pass an event to another
 * element.
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 *
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 * Make sure to allocate an event type with the #GST_EVENT_MAKE_TYPE macro,
 * assigning a free number and filling in the correct direction and
 * serialization flags.
 *
 * New custom events can also be created by subclassing the event type if
 * needed.
 *
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 * Returns: (transfer full): the new custom event.
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 */
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GstEvent *
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gst_event_new_custom (GstEventType type, GstStructure * structure)
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{
  GstEvent *event;

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  /* structure must not have a parent */
  if (structure)
    g_return_val_if_fail (structure->parent_refcount == NULL, NULL);

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  event = gst_event_new (type);
  if (structure) {
    gst_structure_set_parent_refcount (structure, &event->mini_object.refcount);
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    GST_EVENT_STRUCTURE (event) = structure;
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  }
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  return event;
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}

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/**
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 * gst_event_get_structure:
 * @event: The #GstEvent.
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 *
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 * Access the structure of the event.
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 *
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 * Returns: The structure of the event. The structure is still
 * owned by the event, which means that you should not free it and
 * that the pointer becomes invalid when you free the event.
 *
 * MT safe.
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 */
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const GstStructure *
gst_event_get_structure (GstEvent * event)
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{
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  g_return_val_if_fail (GST_IS_EVENT (event), NULL);
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  return GST_EVENT_STRUCTURE (event);
}

/**
 * gst_event_writable_structure:
 * @event: The #GstEvent.
 *
 * Get a writable version of the structure.
 *
 * Returns: The structure of the event. The structure is still
 * owned by the event, which means that you should not free it and
 * that the pointer becomes invalid when you free the event.
 * This function checks if @event is writable and will never return NULL.
 *
 * MT safe.
 */
GstStructure *
gst_event_writable_structure (GstEvent * event)
{
  GstStructure *structure;

  g_return_val_if_fail (GST_IS_EVENT (event), NULL);
  g_return_val_if_fail (gst_event_is_writable (event), NULL);

  structure = GST_EVENT_STRUCTURE (event);

  if (structure == NULL) {
    structure =
        gst_structure_id_empty_new (gst_event_type_to_quark (GST_EVENT_TYPE
            (event)));
    gst_structure_set_parent_refcount (structure, &event->mini_object.refcount);
    GST_EVENT_STRUCTURE (event) = structure;
  }
  return structure;
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}
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/**
 * gst_event_has_name:
 * @event: The #GstEvent.
 * @name: name to check
 *
 * Checks if @event has the given @name. This function is usually used to
 * check the name of a custom event.
 *
 * Returns: %TRUE if @name matches the name of the event structure.
 *
 * Since: 0.10.20
 */
gboolean
gst_event_has_name (GstEvent * event, const gchar * name)
{
  g_return_val_if_fail (GST_IS_EVENT (event), FALSE);

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  if (GST_EVENT_STRUCTURE (event) == NULL)
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    return FALSE;

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  return gst_structure_has_name (GST_EVENT_STRUCTURE (event), name);
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}

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/**
 * gst_event_get_seqnum:
 * @event: A #GstEvent.
 *
 * Retrieve the sequence number of a event.
 *
 * Events have ever-incrementing sequence numbers, which may also be set
 * explicitly via gst_event_set_seqnum(). Sequence numbers are typically used to
 * indicate that a event corresponds to some other set of events or messages,
 * for example an EOS event corresponding to a SEEK event. It is considered good
 * practice to make this correspondence when possible, though it is not
 * required.
 *
 * Note that events and messages share the same sequence number incrementor;
 * two events or messages will never not have the same sequence number unless
 * that correspondence was made explicitly.
 *
 * Returns: The event's sequence number.
 *
 * MT safe.
 *
 * Since: 0.10.22
 */
guint32
gst_event_get_seqnum (GstEvent * event)
{
  g_return_val_if_fail (GST_IS_EVENT (event), -1);

  return GST_EVENT_SEQNUM (event);
}

/**
 * gst_event_set_seqnum:
 * @event: A #GstEvent.
 * @seqnum: A sequence number.
 *
 * Set the sequence number of a event.
 *
 * This function might be called by the creator of a event to indicate that the
 * event relates to other events or messages. See gst_event_get_seqnum() for
 * more information.
 *
 * MT safe.
 *
 * Since: 0.10.22
 */
void
gst_event_set_seqnum (GstEvent * event, guint32 seqnum)
{
  g_return_if_fail (GST_IS_EVENT (event));

  GST_EVENT_SEQNUM (event) = seqnum;
}

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/* FIXME 0.11: It would be nice to have flush events
 * that don't reset the running time in the sinks
 */

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/**
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 * gst_event_new_flush_start:
 *
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 * Allocate a new flush start event. The flush start event can be sent
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 * upstream and downstream and travels out-of-bounds with the dataflow.
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 *
 * It marks pads as being flushing and will make them return
 * #GST_FLOW_WRONG_STATE when used for data flow with gst_pad_push(),
 * gst_pad_chain(), gst_pad_alloc_buffer(), gst_pad_get_range() and
 * gst_pad_pull_range(). Any event (except a #GST_EVENT_FLUSH_STOP) received
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 * on a flushing pad will return %FALSE immediately.
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 *
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 * Elements should unlock any blocking functions and exit their streaming
 * functions as fast as possible when this event is received.
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 *
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 * This event is typically generated after a seek to flush out all queued data
 * in the pipeline so that the new media is played as soon as possible.
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 *
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 * Returns: (transfer full): a new flush start event.
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 */
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GstEvent *
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gst_event_new_flush_start (void)
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{
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  return gst_event_new (GST_EVENT_FLUSH_START);
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}

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/**
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 * gst_event_new_flush_stop:
 *
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 * Allocate a new flush stop event. The flush stop event can be sent
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 * upstream and downstream and travels serialized with the dataflow.
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 * It is typically sent after sending a FLUSH_START event to make the
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 * pads accept data again.
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 *
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 * Elements can process this event synchronized with the dataflow since
 * the preceeding FLUSH_START event stopped the dataflow.
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 *
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 * This event is typically generated to complete a seek and to resume
 * dataflow.
 *
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 * Returns: (transfer full): a new flush stop event.
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 */
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GstEvent *
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gst_event_new_flush_stop (void)
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{
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  return gst_event_new (GST_EVENT_FLUSH_STOP);
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}

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/**
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 * gst_event_new_eos:
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 *
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 * Create a new EOS event. The eos event can only travel downstream
 * synchronized with the buffer flow. Elements that receive the EOS
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 * event on a pad can return #GST_FLOW_UNEXPECTED as a #GstFlowReturn
 * when data after the EOS event arrives.
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 *
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 * The EOS event will travel down to the sink elements in the pipeline
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 * which will then post the #GST_MESSAGE_EOS on the bus after they have
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 * finished playing any buffered data.
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 *
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 * When all sinks have posted an EOS message, an EOS message is
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 * forwarded to the application.
 *
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 * The EOS event itself will not cause any state transitions of the pipeline.
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 *
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 * Returns: (transfer full): the new EOS event.
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 */
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GstEvent *
gst_event_new_eos (void)
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{
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  return gst_event_new (GST_EVENT_EOS);
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}

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/**
 * gst_event_new_caps:
 * @caps: a #GstCaps
 *
 * Create a new CAPS event for @caps. The caps event can only travel downstream
 * synchronized with the buffer flow and contain the format of the buffers
 * that will follow after the event.
 *
 * Returns: (transfer full): the new CAPS event.
 */
GstEvent *
gst_event_new_caps (GstCaps * caps)
{
  GstEvent *event;

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  g_return_val_if_fail (caps != NULL && gst_caps_is_fixed (caps), NULL);

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  GST_CAT_INFO (GST_CAT_EVENT, "creating caps event %" GST_PTR_FORMAT, caps);

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  event = gst_event_new_custom (GST_EVENT_CAPS,
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      gst_structure_id_new (GST_QUARK (EVENT_CAPS),
          GST_QUARK (CAPS), GST_TYPE_CAPS, caps, NULL));

  return event;
}

/**
 * gst_event_parse_caps:
 * @event: The event to parse
 * @caps: (out): A pointer to the caps
 *
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 * Get the caps from @event. The caps remains valid as long as @event remains
 * valid.
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 */
void
gst_event_parse_caps (GstEvent * event, GstCaps ** caps)
{
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  GstStructure *structure;

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  g_return_if_fail (GST_IS_EVENT (event));
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_CAPS);

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  structure = GST_EVENT_STRUCTURE (event);
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  if (G_LIKELY (caps))
    *caps =
        g_value_get_boxed (gst_structure_id_get_value (structure,
            GST_QUARK (CAPS)));
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}

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/**
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 * gst_event_new_new_segment:
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 * @update: Whether this segment is an update to a previous one
 * @rate: A new rate for playback
 * @applied_rate: The rate factor which has already been applied
 * @format: The format of the segment values
 * @start: The start value of the segment
 * @stop: The stop value of the segment
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 * @time: the time value of the segment
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 *
 * Allocate a new newsegment event with the given format/values triplets.
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 *
 * The newsegment event marks the range of buffers to be processed. All
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 * data not within the segment range is not to be processed. This can be
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 * used intelligently by plugins to apply more efficient methods of skipping
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 * unneeded data. The valid range is expressed with the @start and @stop
 * values.
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 *
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 * The time value of the segment is used in conjunction with the start
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 * value to convert the buffer timestamps into the stream time. This is 
 * usually done in sinks to report the current stream_time. 
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 * @time represents the stream_time of a buffer carrying a timestamp of 
 * @start. @time cannot be -1.
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 *
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 * @start cannot be -1, @stop can be -1. If there
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 * is a valid @stop given, it must be greater or equal the @start, including 
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 * when the indicated playback @rate is < 0.
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 *
 * The @applied_rate value provides information about any rate adjustment that
 * has already been made to the timestamps and content on the buffers of the 
 * stream. (@rate * @applied_rate) should always equal the rate that has been 
 * requested for playback. For example, if an element has an input segment 
 * with intended playback @rate of 2.0 and applied_rate of 1.0, it can adjust 
 * incoming timestamps and buffer content by half and output a newsegment event 
 * with @rate of 1.0 and @applied_rate of 2.0
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 *
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 * After a newsegment event, the buffer stream time is calculated with:
 *
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 *   time + (TIMESTAMP(buf) - start) * ABS (rate * applied_rate)
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 *
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 * Returns: (transfer full): a new newsegment event.
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 *
 * Since: 0.10.6
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 */
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GstEvent *
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gst_event_new_new_segment (gboolean update, gdouble rate,
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    gdouble applied_rate, GstFormat format, gint64 start, gint64 stop,
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    gint64 time)
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{
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  GstEvent *event;
  GstStructure *structure;

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  g_return_val_if_fail (rate != 0.0, NULL);
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  g_return_val_if_fail (applied_rate != 0.0, NULL);
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  if (format == GST_FORMAT_TIME) {
    GST_CAT_INFO (GST_CAT_EVENT,
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        "creating newsegment update %d, rate %lf, format GST_FORMAT_TIME, "
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        "start %" GST_TIME_FORMAT ", stop %" GST_TIME_FORMAT
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        ", time %" GST_TIME_FORMAT,
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        update, rate, GST_TIME_ARGS (start),
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        GST_TIME_ARGS (stop), GST_TIME_ARGS (time));
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  } else {
    GST_CAT_INFO (GST_CAT_EVENT,
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        "creating newsegment update %d, rate %lf, format %s, "
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        "start %" G_GINT64_FORMAT ", stop %" G_GINT64_FORMAT ", time %"
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        G_GINT64_FORMAT, update, rate, gst_format_get_name (format), start,
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        stop, time);
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  }
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  g_return_val_if_fail (time != -1, NULL);
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  g_return_val_if_fail (start != -1, NULL);
  if (stop != -1)
    g_return_val_if_fail (start <= stop, NULL);
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  structure = gst_structure_id_new (GST_QUARK (EVENT_NEWSEGMENT),
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      GST_QUARK (UPDATE), G_TYPE_BOOLEAN, update,
      GST_QUARK (RATE), G_TYPE_DOUBLE, rate,
      GST_QUARK (APPLIED_RATE), G_TYPE_DOUBLE, applied_rate,
      GST_QUARK (FORMAT), GST_TYPE_FORMAT, format,
      GST_QUARK (START), G_TYPE_INT64, start,
      GST_QUARK (STOP), G_TYPE_INT64, stop,
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      GST_QUARK (TIME), G_TYPE_INT64, time, NULL);
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  event = gst_event_new_custom (GST_EVENT_NEWSEGMENT, structure);

  return event;
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}
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/**
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 * gst_event_parse_new_segment:
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 * @event: The event to query
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 * @update: (out): A pointer to the update flag of the segment
 * @rate: (out): A pointer to the rate of the segment
 * @applied_rate: (out): A pointer to the applied_rate of the segment
 * @format: (out): A pointer to the format of the newsegment values
 * @start: (out): A pointer to store the start value in
 * @stop: (out): A pointer to store the stop value in
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 * @time: (out): A pointer to store the time value in
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 *
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 * Get the update, rate, applied_rate, format, start, stop and 
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 * time in the newsegment event. See gst_event_new_new_segment() 
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 * for a full description of the newsegment event.
 *
 * Since: 0.10.6
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 */
void
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gst_event_parse_new_segment (GstEvent * event, gboolean * update,
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    gdouble * rate, gdouble * applied_rate, GstFormat * format,
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    gint64 * start, gint64 * stop, gint64 * time)
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{
  const GstStructure *structure;
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  g_return_if_fail (GST_IS_EVENT (event));
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_NEWSEGMENT);

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  structure = GST_EVENT_STRUCTURE (event);
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  if (G_LIKELY (update))
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    *update =
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        g_value_get_boolean (gst_structure_id_get_value (structure,
            GST_QUARK (UPDATE)));
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  if (G_LIKELY (rate))
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    *rate =
        g_value_get_double (gst_structure_id_get_value (structure,
            GST_QUARK (RATE)));
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  if (G_LIKELY (applied_rate))
    *applied_rate =
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        g_value_get_double (gst_structure_id_get_value (structure,
            GST_QUARK (APPLIED_RATE)));
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  if (G_LIKELY (format))
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    *format =
        g_value_get_enum (gst_structure_id_get_value (structure,
            GST_QUARK (FORMAT)));
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  if (G_LIKELY (start))
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    *start =
        g_value_get_int64 (gst_structure_id_get_value (structure,
            GST_QUARK (START)));
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  if (G_LIKELY (stop))
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    *stop =
        g_value_get_int64 (gst_structure_id_get_value (structure,
            GST_QUARK (STOP)));
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  if (G_LIKELY (time))
    *time =
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        g_value_get_int64 (gst_structure_id_get_value (structure,
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            GST_QUARK (TIME)));
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}
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/**
 * gst_event_new_tag:
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 * @taglist: (transfer full): metadata list. The event will take ownership
 *     of the taglist.
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 *
 * Generates a metadata tag event from the given @taglist.
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 *
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 * Returns: (transfer full): a new #GstEvent
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 */
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GstEvent *
gst_event_new_tag (GstTagList * taglist)
{
  g_return_val_if_fail (taglist != NULL, NULL);
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  return gst_event_new_custom (GST_EVENT_TAG, (GstStructure *) taglist);
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}

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/**
 * gst_event_parse_tag:
 * @event: a tag event
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 * @taglist: (out) (transfer none): pointer to metadata list
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 *
 * Parses a tag @event and stores the results in the given @taglist location.
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 * No reference to the taglist will be returned, it remains valid only until
 * the @event is freed. Don't modify or free the taglist, make a copy if you
 * want to modify it or store it for later use.
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 */
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void
gst_event_parse_tag (GstEvent * event, GstTagList ** taglist)
{
  g_return_if_fail (GST_IS_EVENT (event));
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_TAG);
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  if (taglist)
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    *taglist = (GstTagList *) GST_EVENT_STRUCTURE (event);
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}

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/* buffersize event */
/**
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 * gst_event_new_buffer_size:
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 * @format: buffer format
 * @minsize: minimum buffer size
 * @maxsize: maximum buffer size
 * @async: thread behavior
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 *
 * Create a new buffersize event. The event is sent downstream and notifies
 * elements that they should provide a buffer of the specified dimensions.
 *
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 * When the @async flag is set, a thread boundary is prefered.
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 *
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 * Returns: (transfer full): a new #GstEvent
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 */
GstEvent *
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gst_event_new_buffer_size (GstFormat format, gint64 minsize,
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    gint64 maxsize, gboolean async)
{
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  GstEvent *event;
  GstStructure *structure;

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  GST_CAT_INFO (GST_CAT_EVENT,
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      "creating buffersize format %s, minsize %" G_GINT64_FORMAT
      ", maxsize %" G_GINT64_FORMAT ", async %d", gst_format_get_name (format),
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      minsize, maxsize, async);
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  structure = gst_structure_id_new (GST_QUARK (EVENT_BUFFER_SIZE),
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      GST_QUARK (FORMAT), GST_TYPE_FORMAT, format,
      GST_QUARK (MINSIZE), G_TYPE_INT64, minsize,
      GST_QUARK (MAXSIZE), G_TYPE_INT64, maxsize,
      GST_QUARK (ASYNC), G_TYPE_BOOLEAN, async, NULL);
  event = gst_event_new_custom (GST_EVENT_BUFFERSIZE, structure);

  return event;
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}

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/**
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 * gst_event_parse_buffer_size:
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 * @event: The event to query
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 * @format: (out): A pointer to store the format in
 * @minsize: (out): A pointer to store the minsize in
 * @maxsize: (out): A pointer to store the maxsize in
 * @async: (out): A pointer to store the async-flag in
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 *
 * Get the format, minsize, maxsize and async-flag in the buffersize event.
 */
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void
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gst_event_parse_buffer_size (GstEvent * event, GstFormat * format,
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    gint64 * minsize, gint64 * maxsize, gboolean * async)
{
  const GstStructure *structure;

  g_return_if_fail (GST_IS_EVENT (event));
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_BUFFERSIZE);
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  structure = GST_EVENT_STRUCTURE (event);
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  if (format)
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    *format =
        g_value_get_enum (gst_structure_id_get_value (structure,
            GST_QUARK (FORMAT)));
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  if (minsize)
    *minsize =
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        g_value_get_int64 (gst_structure_id_get_value (structure,
            GST_QUARK (MINSIZE)));
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  if (maxsize)
    *maxsize =
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        g_value_get_int64 (gst_structure_id_get_value (structure,
            GST_QUARK (MAXSIZE)));
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  if (async)
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    *async =
        g_value_get_boolean (gst_structure_id_get_value (structure,
            GST_QUARK (ASYNC)));
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}

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/**
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 * gst_event_new_qos:
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 * @type: the QoS type
 * @proportion: the proportion of the qos message
 * @diff: The time difference of the last Clock sync
 * @timestamp: The timestamp of the buffer
 *
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 * Allocate a new qos event with the given values.
 * The QOS event is generated in an element that wants an upstream
 * element to either reduce or increase its rate because of
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 * high/low CPU load or other resource usage such as network performance or
 * throttling. Typically sinks generate these events for each buffer
 * they receive.
 *
 * @type indicates the reason for the QoS event. #GST_QOS_TYPE_OVERFLOW is
 * used when a buffer arrived in time or when the sink cannot keep up with
 * the upstream datarate. #GST_QOS_TYPE_UNDERFLOW is when the sink is not
 * receiving buffers fast enough and thus has to drop late buffers. 
 * #GST_QOS_TYPE_THROTTLE is used when the datarate is artificially limited
 * by the application, for example to reduce power consumption.
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 *
 * @proportion indicates the real-time performance of the streaming in the
 * element that generated the QoS event (usually the sink). The value is
 * generally computed based on more long term statistics about the streams
 * timestamps compared to the clock.
 * A value < 1.0 indicates that the upstream element is producing data faster
 * than real-time. A value > 1.0 indicates that the upstream element is not
 * producing data fast enough. 1.0 is the ideal @proportion value. The
 * proportion value can safely be used to lower or increase the quality of
 * the element.
 *
 * @diff is the difference against the clock in running time of the last
 * buffer that caused the element to generate the QOS event. A negative value
 * means that the buffer with @timestamp arrived in time. A positive value
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 * indicates how late the buffer with @timestamp was. When throttling is
 * enabled, @diff will be set to the requested throttling interval.
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 *
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 * @timestamp is the timestamp of the last buffer that cause the element
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 * to generate the QOS event. It is expressed in running time and thus an ever
 * increasing value.
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 *
 * The upstream element can use the @diff and @timestamp values to decide
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 * whether to process more buffers. For possitive @diff, all buffers with
 * timestamp <= @timestamp + @diff will certainly arrive late in the sink
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 * as well. A (negative) @diff value so that @timestamp + @diff would yield a
 * result smaller than 0 is not allowed.
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 *
 * The application can use general event probes to intercept the QoS
 * event and implement custom application specific QoS handling.
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 *
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 * Returns: (transfer full): a new QOS event.
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 */
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GstEvent *
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gst_event_new_qos (GstQOSType type, gdouble proportion,
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    GstClockTimeDiff diff, GstClockTime timestamp)
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{
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  GstEvent *event;

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  /* diff must be positive or timestamp + diff must be positive */
  g_return_val_if_fail (diff >= 0 || -diff <= timestamp, NULL);

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  GST_CAT_INFO (GST_CAT_EVENT,
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      "creating qos type %d, proportion %lf, diff %" G_GINT64_FORMAT
      ", timestamp %" GST_TIME_FORMAT, type, proportion,
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      diff, GST_TIME_ARGS (timestamp));
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  event = gst_event_new (GST_EVENT_QOS);

  GST_EVENT_IMPL (event, qos, type) = type;
  GST_EVENT_IMPL (event, qos, proportion) = proportion;
  GST_EVENT_IMPL (event, qos, diff) = diff;
  GST_EVENT_IMPL (event, qos, timestamp) = timestamp;
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  return event;
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}
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/**
 * gst_event_parse_qos:
 * @event: The event to query
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 * @type: (out): A pointer to store the QoS type in
 * @proportion: (out): A pointer to store the proportion in
 * @diff: (out): A pointer to store the diff in
 * @timestamp: (out): A pointer to store the timestamp in
 *
 * Get the type, proportion, diff and timestamp in the qos event. See
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 * gst_event_new_qos() for more information about the different QoS values.
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 */
void
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gst_event_parse_qos (GstEvent * event, GstQOSType * type,
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    gdouble * proportion, GstClockTimeDiff * diff, GstClockTime * timestamp)
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{
  g_return_if_fail (GST_IS_EVENT (event));
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_QOS);
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  if (type)
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    *type = GST_EVENT_IMPL (event, qos, type);
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  if (proportion)
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    *proportion = GST_EVENT_IMPL (event, qos, proportion);
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  if (diff)
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    *diff = GST_EVENT_IMPL (event, qos, diff);
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  if (timestamp)
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    *timestamp = GST_EVENT_IMPL (event, qos, timestamp);
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}
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/**
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 * gst_event_new_seek:
 * @rate: The new playback rate
 * @format: The format of the seek values
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 * @flags: The optional seek flags
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 * @start_type: The type and flags for the new start position
 * @start: The value of the new start position
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 * @stop_type: The type and flags for the new stop position
 * @stop: The value of the new stop position
 *
 * Allocate a new seek event with the given parameters.
 *
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 * The seek event configures playback of the pipeline between @start to @stop
 * at the speed given in @rate, also called a playback segment.
 * The @start and @stop values are expressed in @format.
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 *
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 * A @rate of 1.0 means normal playback rate, 2.0 means double speed.
 * Negatives values means backwards playback. A value of 0.0 for the
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 * rate is not allowed and should be accomplished instead by PAUSING the
 * pipeline.
 *
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 * A pipeline has a default playback segment configured with a start
 * position of 0, a stop position of -1 and a rate of 1.0. The currently
 * configured playback segment can be queried with #GST_QUERY_SEGMENT. 
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 *