gstevent.c 65.5 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
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 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
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 */
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/**
 * SECTION:gstevent
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 * @title: 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.
 *
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 * 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,
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 * 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.
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 * To do that gst_event_new_seek() is used to create a seek event. It takes
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 * the needed parameters to specify seeking time and mode.
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 * |[<!-- language="C" -->
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 *   GstEvent *event;
 *   gboolean result;
 *   ...
 *   // construct a seek event to play the media from second 2 to 5, flush
 *   // the pipeline to decrease latency.
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 *   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");
 *   ...
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 * ]|
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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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#include "gstvalue.h"
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GType _gst_event_type = 0;
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typedef struct
{
  GstEvent event;

  GstStructure *structure;
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  gint64 running_time_offset;
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} GstEventImpl;

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#define GST_EVENT_STRUCTURE(e)  (((GstEventImpl *)(e))->structure)
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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},
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  {GST_EVENT_SELECT_STREAMS, "select-streams", 0},
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  {GST_EVENT_STREAM_START, "stream-start", 0},
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  {GST_EVENT_STREAM_COLLECTION, "stream-collection", 0},
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  {GST_EVENT_CAPS, "caps", 0},
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  {GST_EVENT_SEGMENT, "segment", 0},
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  {GST_EVENT_TAG, "tag", 0},
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  {GST_EVENT_TOC, "toc", 0},
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  {GST_EVENT_PROTECTION, "protection", 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_EOS, "eos", 0},
  {GST_EVENT_SEGMENT_DONE, "segment-done", 0},
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  {GST_EVENT_GAP, "gap", 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_TOC_SELECT, "toc-select", 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_DOWNSTREAM_STICKY, "custom-downstream-sticky", 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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  {GST_EVENT_STREAM_GROUP_DONE, "stream-group-done", 0},
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  {0, NULL, 0}
};

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GST_DEFINE_MINI_OBJECT_TYPE (GstEvent, gst_event);
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void
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_priv_gst_event_initialize (void)
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{
  gint i;
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  _gst_event_type = gst_event_get_type ();
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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_NUM_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 (sizeof (GstEventImpl), event);
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}

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static void gst_event_init (GstEventImpl * event, GstEventType type);
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static GstEvent *
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_gst_event_copy (GstEvent * event)
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{
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  GstEventImpl *copy;
  GstStructure *s;
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  copy = g_slice_new0 (GstEventImpl);

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  gst_event_init (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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  } else {
    GST_EVENT_STRUCTURE (copy) = NULL;
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  }
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  ((GstEventImpl *) copy)->running_time_offset =
      ((GstEventImpl *) event)->running_time_offset;

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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, GstEventType type)
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{
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  gst_mini_object_init (GST_MINI_OBJECT_CAST (event), 0, _gst_event_type,
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      (GstMiniObjectCopyFunction) _gst_event_copy, NULL,
      (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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  event->running_time_offset = 0;
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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) (nullable): 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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{
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  GstEventImpl *event;

  event = g_slice_new0 (GstEventImpl);

  GST_CAT_DEBUG (GST_CAT_EVENT, "creating new event %p %s %d", event,
      gst_event_type_get_name (type), type);
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  if (structure) {
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    /* structure must not have a parent */
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    if (!gst_structure_set_parent_refcount (structure,
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            &event->event.mini_object.refcount))
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      goto had_parent;

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  }
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  gst_event_init (event, type);
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  GST_EVENT_STRUCTURE (event) = structure;

  return GST_EVENT_CAST (event);
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  /* ERRORS */
had_parent:
  {
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    g_slice_free1 (sizeof (GstEventImpl), event);
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    g_warning ("structure is already owned by another object");
    return NULL;
  }
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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: (transfer none) (nullable): 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.
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 *
 * 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);
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}

/**
 * gst_event_writable_structure:
 * @event: The #GstEvent.
 *
 * Get a writable version of the structure.
 *
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 * Returns: (transfer none): 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.
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 *
 * 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);

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  structure = GST_EVENT_STRUCTURE (event);
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  if (structure == NULL) {
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    structure =
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        gst_structure_new_id_empty (gst_event_type_to_quark (GST_EVENT_TYPE
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            (event)));
    gst_structure_set_parent_refcount (structure, &event->mini_object.refcount);
    GST_EVENT_STRUCTURE (event) = structure;
  }
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  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.
 */
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;
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 * two events or messages will never have the same sequence number unless
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 * that correspondence was made explicitly.
 *
 * Returns: The event's sequence number.
 *
 * MT safe.
 */
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.
 */
void
gst_event_set_seqnum (GstEvent * event, guint32 seqnum)
{
  g_return_if_fail (GST_IS_EVENT (event));
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  g_return_if_fail (seqnum != GST_SEQNUM_INVALID);
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  GST_EVENT_SEQNUM (event) = seqnum;
}
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/**
 * gst_event_get_running_time_offset:
 * @event: A #GstEvent.
 *
 * Retrieve the accumulated running time offset of the event.
 *
 * Events passing through #GstPads that have a running time
 * offset set via gst_pad_set_offset() will get their offset
 * adjusted according to the pad's offset.
 *
 * If the event contains any information that related to the
 * running time, this information will need to be updated
 * before usage with this offset.
 *
 * Returns: The event's running time offset
 *
 * MT safe.
 *
 * Since: 1.4
 */
gint64
gst_event_get_running_time_offset (GstEvent * event)
{
  g_return_val_if_fail (GST_IS_EVENT (event), 0);

  return ((GstEventImpl *) event)->running_time_offset;
}

/**
 * gst_event_set_running_time_offset:
 * @event: A #GstEvent.
 * @offset: A the new running time offset
 *
 * Set the running time offset of a event. See
 * gst_event_get_running_time_offset() for more information.
 *
 * MT safe.
 *
 * Since: 1.4
 */
void
gst_event_set_running_time_offset (GstEvent * event, gint64 offset)
{
  g_return_if_fail (GST_IS_EVENT (event));

  ((GstEventImpl *) event)->running_time_offset = offset;
}
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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
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 * #GST_FLOW_FLUSHING when used for data flow with gst_pad_push(),
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 * gst_pad_chain(), 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_custom (GST_EVENT_FLUSH_START, NULL);
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}

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/**
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 * gst_event_new_flush_stop:
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 * @reset_time: if time should be reset
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 *
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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
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 * the preceding 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 (gboolean reset_time)
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{
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  GstEvent *event;

  GST_CAT_INFO (GST_CAT_EVENT, "creating flush stop %d", reset_time);

  event = gst_event_new_custom (GST_EVENT_FLUSH_STOP,
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      gst_structure_new_id (GST_QUARK (EVENT_FLUSH_STOP),
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          GST_QUARK (RESET_TIME), G_TYPE_BOOLEAN, reset_time, NULL));

  return event;
}

/**
 * gst_event_parse_flush_stop:
 * @event: The event to parse
 * @reset_time: (out): if time should be reset
 *
 * Parse the FLUSH_STOP event and retrieve the @reset_time member.
 */
void
gst_event_parse_flush_stop (GstEvent * event, gboolean * reset_time)
{
  GstStructure *structure;

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

  structure = GST_EVENT_STRUCTURE (event);
  if (G_LIKELY (reset_time))
    *reset_time =
        g_value_get_boolean (gst_structure_id_get_value (structure,
            GST_QUARK (RESET_TIME)));
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}

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/**
 * gst_event_new_select_streams:
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 * @streams: (element-type utf8) (transfer none): the list of streams to
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 * activate
 *
 * Allocate a new select-streams event.
 *
 * The select-streams event requests the specified @streams to be activated.
 *
 * The list of @streams corresponds to the "Stream ID" of each stream to be
 * activated. Those ID can be obtained via the #GstStream objects present
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 * in #GST_EVENT_STREAM_START, #GST_EVENT_STREAM_COLLECTION or
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 * #GST_MESSAGE_STREAM_COLLECTION.
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 *
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 * Note: The list of @streams can not be empty.
 *
 * Returns: (transfer full): a new select-streams event or %NULL in case of
 * an error (like an empty streams list).
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 *
 * Since: 1.10
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 */
GstEvent *
gst_event_new_select_streams (GList * streams)
{
  GstEvent *event;
  GValue val = G_VALUE_INIT;
  GstStructure *struc;
  GList *tmpl;

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  g_return_val_if_fail (streams != NULL, NULL);

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  GST_CAT_INFO (GST_CAT_EVENT, "Creating new select-streams event");
  struc = gst_structure_new_id_empty (GST_QUARK (EVENT_SELECT_STREAMS));
  g_value_init (&val, GST_TYPE_LIST);
  /* Fill struc with streams */
  for (tmpl = streams; tmpl; tmpl = tmpl->next) {
    GValue strval = G_VALUE_INIT;
    const gchar *str = (const gchar *) tmpl->data;
    g_value_init (&strval, G_TYPE_STRING);
    g_value_set_string (&strval, str);
    gst_value_list_append_and_take_value (&val, &strval);
  }
  gst_structure_id_take_value (struc, GST_QUARK (STREAMS), &val);
  event = gst_event_new_custom (GST_EVENT_SELECT_STREAMS, struc);

  return event;
}

/**
 * gst_event_parse_select_streams:
 * @event: The event to parse
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 * @streams: (out) (element-type utf8) (transfer full): the streams
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 *
 * Parse the SELECT_STREAMS event and retrieve the contained streams.
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 *
 * Since: 1.10
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 */
void
gst_event_parse_select_streams (GstEvent * event, GList ** streams)
{
  GstStructure *structure;
  GList *res = NULL;

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

  structure = GST_EVENT_STRUCTURE (event);
  if (G_LIKELY (streams)) {
    const GValue *vlist =
        gst_structure_id_get_value (structure, GST_QUARK (STREAMS));
    guint i, sz = gst_value_list_get_size (vlist);
    for (i = 0; i < sz; i++) {
      const GValue *strv = gst_value_list_get_value (vlist, i);
      res = g_list_append (res, g_value_dup_string (strv));
    }
    *streams = res;
  }
}


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/**
 * gst_event_new_stream_group_done:
 * @group_id: the group id of the stream group which is ending
 *
 * Create a new Stream Group Done event. The stream-group-done event can
 * only travel downstream synchronized with the buffer flow. Elements
 * that receive the event on a pad should handle it mostly like EOS,
 * and emit any data or pending buffers that would depend on more data
 * arriving and unblock, since there won't be any more data.
 *
 * This event is followed by EOS at some point in the future, and is
 * generally used when switching pads - to unblock downstream so that
 * new pads can be exposed before sending EOS on the existing pads.
 *
 * Returns: (transfer full): the new stream-group-done event.
 *
 * Since: 1.10
 */
GstEvent *
gst_event_new_stream_group_done (guint group_id)
{
  GstStructure *s;

  s = gst_structure_new_id (GST_QUARK (EVENT_STREAM_GROUP_DONE),
      GST_QUARK (GROUP_ID), G_TYPE_UINT, group_id, NULL);

  return gst_event_new_custom (GST_EVENT_STREAM_GROUP_DONE, s);
}

/**
 * gst_event_parse_stream_group_done:
 * @event: a stream-group-done event.
 * @group_id: (out): address of variable to store the group id into
 *
 * Parse a stream-group-done @event and store the result in the given
 * @group_id location.
 *
 * Since: 1.10
 */
void
gst_event_parse_stream_group_done (GstEvent * event, guint * group_id)
{
  g_return_if_fail (event != NULL);
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_STREAM_GROUP_DONE);

  if (group_id) {
    gst_structure_id_get (GST_EVENT_STRUCTURE (event),
        GST_QUARK (GROUP_ID), G_TYPE_UINT, group_id, NULL);
  }
}

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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_EOS as a #GstFlowReturn
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 * 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_custom (GST_EVENT_EOS, NULL);
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}

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/**
 * gst_event_new_gap:
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 * @timestamp: the start time (pts) of the gap
 * @duration: the duration of the gap
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 *
 * Create a new GAP event. A gap event can be thought of as conceptually
 * equivalent to a buffer to signal that there is no data for a certain
 * amount of time. This is useful to signal a gap to downstream elements
 * which may wait for data, such as muxers or mixers or overlays, especially
 * for sparse streams such as subtitle streams.
 *
 * Returns: (transfer full): the new GAP event.
 */
GstEvent *
gst_event_new_gap (GstClockTime timestamp, GstClockTime duration)
{
  GstEvent *event;

  g_return_val_if_fail (GST_CLOCK_TIME_IS_VALID (timestamp), NULL);

  GST_CAT_TRACE (GST_CAT_EVENT, "creating gap %" GST_TIME_FORMAT " - "
      "%" GST_TIME_FORMAT " (duration: %" GST_TIME_FORMAT ")",
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      GST_TIME_ARGS (timestamp), GST_TIME_ARGS (timestamp + duration),
      GST_TIME_ARGS (duration));
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  event = gst_event_new_custom (GST_EVENT_GAP,
      gst_structure_new_id (GST_QUARK (EVENT_GAP),
          GST_QUARK (TIMESTAMP), GST_TYPE_CLOCK_TIME, timestamp,
          GST_QUARK (DURATION), GST_TYPE_CLOCK_TIME, duration, NULL));

  return event;
}

/**
 * gst_event_parse_gap:
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 * @event: a #GstEvent of type #GST_EVENT_GAP
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 * @timestamp: (out) (allow-none): location where to store the
 *     start time (pts) of the gap, or %NULL
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 * @duration: (out) (allow-none): location where to store the duration of
 *     the gap, or %NULL
 *
 * Extract timestamp and duration from a new GAP event.
 */
void
gst_event_parse_gap (GstEvent * event, GstClockTime * timestamp,
    GstClockTime * duration)
{
  GstStructure *structure;

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

  structure = GST_EVENT_STRUCTURE (event);
  gst_structure_id_get (structure,
      GST_QUARK (TIMESTAMP), GST_TYPE_CLOCK_TIME, timestamp,
      GST_QUARK (DURATION), GST_TYPE_CLOCK_TIME, duration, NULL);
}

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/**
 * gst_event_new_caps:
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 * @caps: (transfer none): a #GstCaps
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 *
 * Create a new CAPS event for @caps. The caps event can only travel downstream
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 * synchronized with the buffer flow and contains the format of the buffers
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 * that will follow after the event.
 *
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 * Returns: (transfer full) (nullable): the new CAPS event.
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 */
GstEvent *
gst_event_new_caps (GstCaps * caps)
{
  GstEvent *event;

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  g_return_val_if_fail (caps != NULL, NULL);
  g_return_val_if_fail (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_new_id (GST_QUARK (EVENT_CAPS),
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          GST_QUARK (CAPS), GST_TYPE_CAPS, caps, NULL));

  return event;
}

/**
 * gst_event_parse_caps:
 * @event: The event to parse
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 * @caps: (out) (transfer none): A pointer to the caps
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 *
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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_segment:
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 * @segment: (transfer none): a #GstSegment
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 *
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 * Create a new SEGMENT event for @segment. The segment event can only travel
 * downstream synchronized with the buffer flow and contains timing information
 * and playback properties for the buffers that will follow.
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 *
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 * The segment 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.
 * @time represents the stream_time of a buffer carrying a timestamp of
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 * @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
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 * 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
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 * incoming timestamps and buffer content by half and output a segment event
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 * with @rate of 1.0 and @applied_rate of 2.0
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 *
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 * After a segment event, the buffer stream time is calculated with:
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 *
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 *   time + (TIMESTAMP(buf) - start) * ABS (rate * applied_rate)
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 *
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 * Returns: (transfer full) (nullable): the new SEGMENT event.
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 */
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GstEvent *
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gst_event_new_segment (const GstSegment * segment)
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{
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  GstEvent *event;

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  g_return_val_if_fail (segment != NULL, NULL);
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  g_return_val_if_fail (segment->rate != 0.0, NULL);
  g_return_val_if_fail (segment->applied_rate != 0.0, NULL);
  g_return_val_if_fail (segment->format != GST_FORMAT_UNDEFINED, NULL);
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  GST_CAT_INFO (GST_CAT_EVENT, "creating segment event %" GST_SEGMENT_FORMAT,
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      segment);

  event = gst_event_new_custom (GST_EVENT_SEGMENT,
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      gst_structure_new_id (GST_QUARK (EVENT_SEGMENT),
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          GST_QUARK (SEGMENT), GST_TYPE_SEGMENT, segment, NULL));
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  return event;
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}
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/**
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 * gst_event_parse_segment:
 * @event: The event to parse
 * @segment: (out) (transfer none): a pointer to a #GstSegment
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 *
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 * Parses a segment @event and stores the result in the given @segment location.
 * @segment remains valid only until the @event is freed. Don't modify the segment
 * and 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_segment (GstEvent * event, const GstSegment ** segment)
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{
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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_SEGMENT);
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  if (segment) {
    structure = GST_EVENT_STRUCTURE (event);
    *segment = g_value_get_boxed (gst_structure_id_get_value (structure,
            GST_QUARK (SEGMENT)));
  }
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}

/**
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 * gst_event_copy_segment:
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 * @event: The event to parse
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 * @segment: a pointer to a #GstSegment
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 *
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 * Parses a segment @event and copies the #GstSegment into the location
 * given by @segment.
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 */
void
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gst_event_copy_segment (GstEvent * event, GstSegment * segment)
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{
  const GstSegment *src;

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  g_return_if_fail (GST_IS_EVENT (event));
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_SEGMENT);
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  if (segment) {
    gst_event_parse_segment (event, &src);
    gst_segment_copy_into (src, segment);
  }
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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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 * The scope of the taglist specifies if the taglist applies to the
 * complete medium or only to this specific stream. As the tag event
 * is a sticky event, elements should merge tags received from
 * upstream with a given scope with their own tags with the same
 * scope and create a new tag event from it.
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 *
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 * Returns: (transfer full): a new #GstEvent
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 */
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GstEvent *
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gst_event_new_tag (GstTagList * taglist)
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{
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  GstStructure *s;
  GValue val = G_VALUE_INIT;
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  const gchar *names[] = { "GstTagList-stream", "GstTagList-global" };
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  g_return_val_if_fail (taglist != NULL, NULL);
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  s = gst_structure_new_empty (names[gst_tag_list_get_scope (taglist)]);
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  g_value_init (&val, GST_TYPE_TAG_LIST);
  g_value_take_boxed (&val, taglist);
  gst_structure_id_take_value (s, GST_QUARK (TAGLIST), &val);
  return gst_event_new_custom (GST_EVENT_TAG, s);
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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)
{
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  const GValue *val;

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  g_return_if_fail (GST_IS_EVENT (event));
  g_return_if_fail (GST_EVENT_TYPE (event) == GST_EVENT_TAG);
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  val = gst_structure_id_get_value (GST_EVENT_STRUCTURE (event),
      GST_QUARK (TAGLIST));

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  if (taglist)
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    *taglist = (GstTagList *) g_value_get_boxed (val);
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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 preferred.
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 *
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 * Returns: (transfer full): a new #GstEvent
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 */
GstEvent *