gstreamer/gst/gstmessage.c

/* GStreamer
 * Copyright (C) 2004 Wim Taymans <wim@fluendo.com>
 *
 * gstmessage.c: GstMessage subsystem
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/**
 * SECTION:gstmessage
 * @short_description: Lightweight objects to signal the application of
 *                     pipeline events
 * @see_also: #GstBus, #GstMiniObject, #GstElement
 *
 * Messages are implemented as a subclass of #GstMiniObject with a generic
 * #GstStructure as the content. This allows for writing custom messages without
 * requiring an API change while allowing a wide range of different types
 * of messages.
 *
 * Messages are posted by objects in the pipeline and are passed to the
 * application using the #GstBus.

 * The basic use pattern of posting a message on a #GstBus is as follows:
 *
 * <example>
 * <title>Posting a #GstMessage</title>
 *   <programlisting>
 *    gst_bus_post (bus, gst_message_new_eos());
 *   </programlisting>
 * </example>
 *
 * A #GstElement usually posts messages on the bus provided by the parent
 * container using gst_element_post_message().
 *
 * Last reviewed on 2005-11-09 (0.9.4)
 */


#include "gst_private.h"
#include <string.h>             /* memcpy */
#include "gsterror.h"
#include "gstenumtypes.h"
#include "gstinfo.h"
#include "gstmessage.h"
#include "gsttaglist.h"
#include "gstutils.h"
#include "gstquark.h"


#define GST_MESSAGE_SEQNUM(e) ((GstMessage*)e)->abidata.ABI.seqnum

static void gst_message_init (GTypeInstance * instance, gpointer g_class);
static void gst_message_class_init (gpointer g_class, gpointer class_data);
static void gst_message_finalize (GstMessage * message);
static GstMessage *_gst_message_copy (GstMessage * message);

static GstMiniObjectClass *parent_class = NULL;

void
_gst_message_initialize (void)
{
  GST_CAT_INFO (GST_CAT_GST_INIT, "init messages");

  /* the GstMiniObject types need to be class_ref'd once before it can be
   * done from multiple threads;
   * see http://bugzilla.gnome.org/show_bug.cgi?id=304551 */
  g_type_class_ref (gst_message_get_type ());
}

typedef struct
{
  const gint type;
  const gchar *name;
  GQuark quark;
} GstMessageQuarks;

static GstMessageQuarks message_quarks[] = {
  {GST_MESSAGE_UNKNOWN, "unknown", 0},
  {GST_MESSAGE_EOS, "eos", 0},
  {GST_MESSAGE_ERROR, "error", 0},
  {GST_MESSAGE_WARNING, "warning", 0},
  {GST_MESSAGE_INFO, "info", 0},
  {GST_MESSAGE_TAG, "tag", 0},
  {GST_MESSAGE_BUFFERING, "buffering", 0},
  {GST_MESSAGE_STATE_CHANGED, "state-changed", 0},
  {GST_MESSAGE_STATE_DIRTY, "state-dirty", 0},
  {GST_MESSAGE_STEP_DONE, "step-done", 0},
  {GST_MESSAGE_CLOCK_PROVIDE, "clock-provide", 0},
  {GST_MESSAGE_CLOCK_LOST, "clock-lost", 0},
  {GST_MESSAGE_NEW_CLOCK, "new-clock", 0},
  {GST_MESSAGE_STRUCTURE_CHANGE, "structure-change", 0},
  {GST_MESSAGE_STREAM_STATUS, "stream-status", 0},
  {GST_MESSAGE_APPLICATION, "application", 0},
  {GST_MESSAGE_ELEMENT, "element", 0},
  {GST_MESSAGE_SEGMENT_START, "segment-start", 0},
  {GST_MESSAGE_SEGMENT_DONE, "segment-done", 0},
  {GST_MESSAGE_DURATION, "duration", 0},
  {GST_MESSAGE_LATENCY, "latency", 0},
  {GST_MESSAGE_ASYNC_START, "async-start", 0},
  {GST_MESSAGE_ASYNC_DONE, "async-done", 0},
  {GST_MESSAGE_REQUEST_STATE, "request-state", 0},
  {0, NULL, 0}
};

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

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

/**
 * gst_message_type_to_quark:
 * @type: the message type
 *
 * Get the unique quark for the given message type.
 *
 * Returns: the quark associated with the message type
 */
GQuark
gst_message_type_to_quark (GstMessageType type)
{
  gint i;

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

GType
gst_message_get_type (void)
{
  static GType _gst_message_type;

  if (G_UNLIKELY (_gst_message_type == 0)) {
    gint i;
    static const GTypeInfo message_info = {
      sizeof (GstMessageClass),
      NULL,
      NULL,
      gst_message_class_init,
      NULL,
      NULL,
      sizeof (GstMessage),
      0,
      gst_message_init,
      NULL
    };

    _gst_message_type = g_type_register_static (GST_TYPE_MINI_OBJECT,
        "GstMessage", &message_info, 0);

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

static void
gst_message_class_init (gpointer g_class, gpointer class_data)
{
  GstMessageClass *message_class = GST_MESSAGE_CLASS (g_class);

  parent_class = g_type_class_peek_parent (g_class);

  message_class->mini_object_class.copy =
      (GstMiniObjectCopyFunction) _gst_message_copy;
  message_class->mini_object_class.finalize =
      (GstMiniObjectFinalizeFunction) gst_message_finalize;
}

static void
gst_message_init (GTypeInstance * instance, gpointer g_class)
{
  GstMessage *message = GST_MESSAGE (instance);

  GST_CAT_LOG (GST_CAT_MESSAGE, "new message %p", message);
  GST_MESSAGE_TIMESTAMP (message) = GST_CLOCK_TIME_NONE;
}

static void
gst_message_finalize (GstMessage * message)
{
  g_return_if_fail (message != NULL);

  GST_CAT_LOG (GST_CAT_MESSAGE, "finalize message %p", message);

  if (GST_MESSAGE_SRC (message)) {
    gst_object_unref (GST_MESSAGE_SRC (message));
    GST_MESSAGE_SRC (message) = NULL;
  }

  if (message->lock) {
    GST_MESSAGE_LOCK (message);
    GST_MESSAGE_SIGNAL (message);
    GST_MESSAGE_UNLOCK (message);
  }

  if (message->structure) {
    gst_structure_set_parent_refcount (message->structure, NULL);
    gst_structure_free (message->structure);
  }

  GST_MINI_OBJECT_CLASS (parent_class)->finalize (GST_MINI_OBJECT (message));
}

static GstMessage *
_gst_message_copy (GstMessage * message)
{
  GstMessage *copy;

  GST_CAT_LOG (GST_CAT_MESSAGE, "copy message %p", message);

  copy = (GstMessage *) gst_mini_object_new (GST_TYPE_MESSAGE);

  /* FIXME, need to copy relevant data from the miniobject. */
  //memcpy (copy, message, sizeof (GstMessage));

  GST_MESSAGE_GET_LOCK (copy) = GST_MESSAGE_GET_LOCK (message);
  GST_MESSAGE_COND (copy) = GST_MESSAGE_COND (message);
  GST_MESSAGE_TYPE (copy) = GST_MESSAGE_TYPE (message);
  GST_MESSAGE_TIMESTAMP (copy) = GST_MESSAGE_TIMESTAMP (message);
  GST_MESSAGE_SEQNUM (copy) = GST_MESSAGE_SEQNUM (message);

  if (GST_MESSAGE_SRC (message)) {
    GST_MESSAGE_SRC (copy) = gst_object_ref (GST_MESSAGE_SRC (message));
  }

  if (message->structure) {
    copy->structure = gst_structure_copy (message->structure);
    gst_structure_set_parent_refcount (copy->structure,
        &copy->mini_object.refcount);
  }

  return copy;
}

/**
 * gst_message_new_custom:
 * @type: The #GstMessageType to distinguish messages
 * @src: The object originating the message.
 * @structure: The structure for the message. The message will take ownership of
 * the structure.
 *
 * Create a new custom-typed message. This can be used for anything not
 * handled by other message-specific functions to pass a message to the
 * app. The structure field can be NULL.
 *
 * Returns: The new message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_custom (GstMessageType type, GstObject * src,
    GstStructure * structure)
{
  GstMessage *message;

  message = (GstMessage *) gst_mini_object_new (GST_TYPE_MESSAGE);

  GST_CAT_LOG (GST_CAT_MESSAGE, "source %s: creating new message %p %s",
      (src ? GST_OBJECT_NAME (src) : "NULL"), message,
      gst_message_type_get_name (type));

  message->type = type;

  if (src)
    gst_object_ref (src);
  message->src = src;

  if (structure) {
    gst_structure_set_parent_refcount (structure,
        &message->mini_object.refcount);
  }
  message->structure = structure;

  GST_MESSAGE_SEQNUM (message) = gst_util_seqnum_next ();

  return message;
}

/**
 * gst_message_get_seqnum:
 * @message: A #GstMessage.
 *
 * Retrieve the sequence number of a message.
 *
 * Messages have ever-incrementing sequence numbers, which may also be set
 * explicitly via gst_message_set_seqnum(). Sequence numbers are typically used
 * to indicate that a message corresponds to some other set of messages or
 * events, for example a SEGMENT_DONE message 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 message's sequence number.
 *
 * Since: 0.10.22
 *
 * MT safe.
 */
guint32
gst_message_get_seqnum (GstMessage * message)
{
  g_return_val_if_fail (GST_IS_MESSAGE (message), -1);

  return GST_MESSAGE_SEQNUM (message);
}

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

  GST_MESSAGE_SEQNUM (message) = seqnum;
}

/**
 * gst_message_new_eos:
 * @src: The object originating the message.
 *
 * Create a new eos message. This message is generated and posted in
 * the sink elements of a GstBin. The bin will only forward the EOS
 * message to the application if all sinks have posted an EOS message.
 *
 * Returns: The new eos message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_eos (GstObject * src)
{
  GstMessage *message;

  message = gst_message_new_custom (GST_MESSAGE_EOS, src, NULL);

  return message;
}

/**
 * gst_message_new_error:
 * @src: The object originating the message.
 * @error: The GError for this message.
 * @debug: A debugging string.
 *
 * Create a new error message. The message will copy @error and
 * @debug. This message is posted by element when a fatal event
 * occured. The pipeline will probably (partially) stop. The application
 * receiving this message should stop the pipeline.
 *
 * Returns: The new error message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_error (GstObject * src, GError * error, const gchar * debug)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageError");
  gst_structure_id_set (structure,
      GST_QUARK (GERROR), GST_TYPE_G_ERROR, error,
      GST_QUARK (DEBUG), G_TYPE_STRING, debug, NULL);
  message = gst_message_new_custom (GST_MESSAGE_ERROR, src, structure);

  return message;
}

/**
 * gst_message_new_warning:
 * @src: The object originating the message.
 * @error: The GError for this message.
 * @debug: A debugging string.
 *
 * Create a new warning message. The message will make copies of @error and
 * @debug.
 *
 * Returns: The new warning message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_warning (GstObject * src, GError * error, const gchar * debug)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageWarning");
  gst_structure_id_set (structure,
      GST_QUARK (GERROR), GST_TYPE_G_ERROR, error,
      GST_QUARK (DEBUG), G_TYPE_STRING, debug, NULL);
  message = gst_message_new_custom (GST_MESSAGE_WARNING, src, structure);

  return message;
}

/**
 * gst_message_new_info:
 * @src: The object originating the message.
 * @error: The GError for this message.
 * @debug: A debugging string.
 *
 * Create a new info message. The message will make copies of @error and
 * @debug.
 *
 * Returns: The new info message.
 *
 * Since: 0.10.12
 *
 * MT safe.
 */
GstMessage *
gst_message_new_info (GstObject * src, GError * error, const gchar * debug)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageInfo");
  gst_structure_id_set (structure, GST_QUARK (GERROR), GST_TYPE_G_ERROR,
      error, GST_QUARK (DEBUG), G_TYPE_STRING, debug, NULL);
  message = gst_message_new_custom (GST_MESSAGE_INFO, src, structure);

  return message;
}

/**
 * gst_message_new_tag:
 * @src: The object originating the message.
 * @tag_list: The tag list for the message.
 *
 * Create a new tag message. The message will take ownership of the tag list.
 * The message is posted by elements that discovered a new taglist.
 *
 * Returns: The new tag message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_tag (GstObject * src, GstTagList * tag_list)
{
  GstMessage *message;

  g_return_val_if_fail (GST_IS_STRUCTURE (tag_list), NULL);

  message =
      gst_message_new_custom (GST_MESSAGE_TAG, src, (GstStructure *) tag_list);

  return message;
}

/**
 * gst_message_new_buffering:
 * @src: The object originating the message.
 * @percent: The buffering percent
 *
 * Create a new buffering message. This message can be posted by an element that
 * needs to buffer data before it can continue processing. @percent should be a
 * value between 0 and 100. A value of 100 means that the buffering completed.
 *
 * When @percent is < 100 the application should PAUSE a PLAYING pipeline. When
 * @percent is 100, the application can set the pipeline (back) to PLAYING.
 * The application must be prepared to receive BUFFERING messages in the
 * PREROLLING state and may only set the pipeline to PLAYING after receiving a
 * message with @percent set to 100, which can happen after the pipeline
 * completed prerolling. 
 *
 * Returns: The new buffering message.
 *
 * Since: 0.10.11
 *
 * MT safe.
 */
GstMessage *
gst_message_new_buffering (GstObject * src, gint percent)
{
  GstMessage *message;
  GstStructure *structure;

  g_return_val_if_fail (percent >= 0 && percent <= 100, NULL);

  structure = gst_structure_empty_new ("GstMessageBuffering");
  gst_structure_id_set (structure,
      GST_QUARK (BUFFER_PERCENT), G_TYPE_INT, percent,
      GST_QUARK (BUFFERING_MODE), GST_TYPE_BUFFERING_MODE, GST_BUFFERING_STREAM,
      GST_QUARK (AVG_IN_RATE), G_TYPE_INT, -1,
      GST_QUARK (AVG_OUT_RATE), G_TYPE_INT, -1,
      GST_QUARK (BUFFERING_LEFT), G_TYPE_INT64, G_GINT64_CONSTANT (-1),
      GST_QUARK (ESTIMATED_TOTAL), G_TYPE_INT64, G_GINT64_CONSTANT (-1), NULL);
  message = gst_message_new_custom (GST_MESSAGE_BUFFERING, src, structure);

  return message;
}

/**
 * gst_message_new_state_changed:
 * @src: the object originating the message
 * @oldstate: the previous state
 * @newstate: the new (current) state
 * @pending: the pending (target) state
 *
 * Create a state change message. This message is posted whenever an element
 * changed its state.
 *
 * Returns: The new state change message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_state_changed (GstObject * src,
    GstState oldstate, GstState newstate, GstState pending)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageState");
  gst_structure_id_set (structure,
      GST_QUARK (OLD_STATE), GST_TYPE_STATE, (gint) oldstate,
      GST_QUARK (NEW_STATE), GST_TYPE_STATE, (gint) newstate,
      GST_QUARK (PENDING_STATE), GST_TYPE_STATE, (gint) pending, NULL);
  message = gst_message_new_custom (GST_MESSAGE_STATE_CHANGED, src, structure);

  return message;
}

/**
 * gst_message_new_state_dirty:
 * @src: the object originating the message
 *
 * Create a state dirty message. This message is posted whenever an element
 * changed its state asynchronously and is used internally to update the
 * states of container objects.
 *
 * Returns: The new state dirty message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_state_dirty (GstObject * src)
{
  GstMessage *message;

  message = gst_message_new_custom (GST_MESSAGE_STATE_DIRTY, src, NULL);

  return message;
}

/**
 * gst_message_new_clock_provide:
 * @src: The object originating the message.
 * @clock: The clock it provides
 * @ready: TRUE if the sender can provide a clock
 *
 * Create a clock provide message. This message is posted whenever an
 * element is ready to provide a clock or lost its ability to provide
 * a clock (maybe because it paused or became EOS).
 *
 * This message is mainly used internally to manage the clock
 * selection.
 *
 * Returns: The new provide clock message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_clock_provide (GstObject * src, GstClock * clock,
    gboolean ready)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageClockProvide");
  gst_structure_id_set (structure,
      GST_QUARK (CLOCK), GST_TYPE_CLOCK, clock,
      GST_QUARK (READY), G_TYPE_BOOLEAN, ready, NULL);
  message = gst_message_new_custom (GST_MESSAGE_CLOCK_PROVIDE, src, structure);

  return message;
}

/**
 * gst_message_new_clock_lost:
 * @src: The object originating the message.
 * @clock: the clock that was lost
 *
 * Create a clock lost message. This message is posted whenever the
 * clock is not valid anymore.
 *
 * If this message is posted by the pipeline, the pipeline will
 * select a new clock again when it goes to PLAYING. It might therefore
 * be needed to set the pipeline to PAUSED and PLAYING again.
 *
 * Returns: The new clock lost message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_clock_lost (GstObject * src, GstClock * clock)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageClockLost");
  gst_structure_id_set (structure,
      GST_QUARK (CLOCK), GST_TYPE_CLOCK, clock, NULL);
  message = gst_message_new_custom (GST_MESSAGE_CLOCK_LOST, src, structure);

  return message;
}

/**
 * gst_message_new_new_clock:
 * @src: The object originating the message.
 * @clock: the new selected clock
 *
 * Create a new clock message. This message is posted whenever the
 * pipeline selectes a new clock for the pipeline.
 *
 * Returns: The new new clock message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_new_clock (GstObject * src, GstClock * clock)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageNewClock");
  gst_structure_id_set (structure,
      GST_QUARK (CLOCK), GST_TYPE_CLOCK, clock, NULL);
  message = gst_message_new_custom (GST_MESSAGE_NEW_CLOCK, src, structure);

  return message;
}

/**
 * gst_message_new_structure_change:
 * @src: The object originating the message.
 * @type: The change type.
 * @owner: The owner element of @src.
 * @busy: Whether the structure change is busy.
 *
 * Create a new structure change message. This message is posted when the
 * structure of a pipeline is in the process of being changed, for example
 * when pads are linked or unlinked.
 *
 * @src should be the srcpad that unlinked or linked.
 *
 * Returns: The new structure change message.
 *
 * MT safe.
 *
 * Since: 0.10.22.
 */
GstMessage *
gst_message_new_structure_change (GstObject * src, GstStructureChangeType type,
    GstElement * owner, gboolean busy)
{
  GstMessage *message;
  GstStructure *structure;

  g_return_val_if_fail (GST_IS_PAD (src), NULL);
  g_return_val_if_fail (GST_PAD_DIRECTION (src) == GST_PAD_SRC, NULL);
  g_return_val_if_fail (GST_IS_ELEMENT (owner), NULL);

  structure = gst_structure_empty_new ("GstMessageStructureChange");
  gst_structure_id_set (structure,
      GST_QUARK (TYPE), GST_TYPE_STRUCTURE_CHANGE_TYPE, type,
      GST_QUARK (OWNER), GST_TYPE_ELEMENT, owner,
      GST_QUARK (BUSY), G_TYPE_BOOLEAN, busy, NULL);

  message = gst_message_new_custom (GST_MESSAGE_STRUCTURE_CHANGE, src,
      structure);

  return message;
}

/**
 * gst_message_new_segment_start:
 * @src: The object originating the message.
 * @format: The format of the position being played
 * @position: The position of the segment being played
 *
 * Create a new segment message. This message is posted by elements that
 * start playback of a segment as a result of a segment seek. This message
 * is not received by the application but is used for maintenance reasons in
 * container elements.
 *
 * Returns: The new segment start message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_segment_start (GstObject * src, GstFormat format,
    gint64 position)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageSegmentStart");
  gst_structure_id_set (structure,
      GST_QUARK (FORMAT), GST_TYPE_FORMAT, format,
      GST_QUARK (POSITION), G_TYPE_INT64, position, NULL);
  message = gst_message_new_custom (GST_MESSAGE_SEGMENT_START, src, structure);

  return message;
}

/**
 * gst_message_new_segment_done:
 * @src: The object originating the message.
 * @format: The format of the position being done
 * @position: The position of the segment being done
 *
 * Create a new segment done message. This message is posted by elements that
 * finish playback of a segment as a result of a segment seek. This message
 * is received by the application after all elements that posted a segment_start
 * have posted the segment_done.
 *
 * Returns: The new segment done message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_segment_done (GstObject * src, GstFormat format,
    gint64 position)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageSegmentDone");
  gst_structure_id_set (structure,
      GST_QUARK (FORMAT), GST_TYPE_FORMAT, format,
      GST_QUARK (POSITION), G_TYPE_INT64, position, NULL);
  message = gst_message_new_custom (GST_MESSAGE_SEGMENT_DONE, src, structure);

  return message;
}

/**
 * gst_message_new_application:
 * @src: The object originating the message.
 * @structure: The structure for the message. The message will take ownership of
 * the structure.
 *
 * Create a new application-typed message. GStreamer will never create these
 * messages; they are a gift from us to you. Enjoy.
 *
 * Returns: The new application message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_application (GstObject * src, GstStructure * structure)
{
  return gst_message_new_custom (GST_MESSAGE_APPLICATION, src, structure);
}

/**
 * gst_message_new_element:
 * @src: The object originating the message.
 * @structure: The structure for the message. The message will take ownership of
 * the structure.
 *
 * Create a new element-specific message. This is meant as a generic way of
 * allowing one-way communication from an element to an application, for example
 * "the firewire cable was unplugged". The format of the message should be
 * documented in the element's documentation. The structure field can be NULL.
 *
 * Returns: The new element message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_element (GstObject * src, GstStructure * structure)
{
  return gst_message_new_custom (GST_MESSAGE_ELEMENT, src, structure);
}

/**
 * gst_message_new_duration:
 * @src: The object originating the message.
 * @format: The format of the duration
 * @duration: The new duration 
 *
 * Create a new duration message. This message is posted by elements that
 * know the duration of a stream in a specific format. This message
 * is received by bins and is used to calculate the total duration of a
 * pipeline. Elements may post a duration message with a duration of
 * GST_CLOCK_TIME_NONE to indicate that the duration has changed and the 
 * cached duration should be discarded. The new duration can then be 
 * retrieved via a query.
 *
 * Returns: The new duration message.
 *
 * MT safe.
 */
GstMessage *
gst_message_new_duration (GstObject * src, GstFormat format, gint64 duration)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageDuration");
  gst_structure_id_set (structure,
      GST_QUARK (FORMAT), GST_TYPE_FORMAT, format,
      GST_QUARK (DURATION), G_TYPE_INT64, duration, NULL);
  message = gst_message_new_custom (GST_MESSAGE_DURATION, src, structure);

  return message;
}

/**
 * gst_message_new_async_start:
 * @src: The object originating the message.
 * @new_base_time: if a new base_time should be set on the element
 *
 * This message is posted by elements when they start an ASYNC state change. 
 * @new_base_time is set to TRUE when the element lost its state when it was
 * PLAYING.
 *
 * Returns: The new async_start message. 
 *
 * MT safe.
 *
 * Since: 0.10.13
 */
GstMessage *
gst_message_new_async_start (GstObject * src, gboolean new_base_time)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageAsyncStart");
  gst_structure_id_set (structure,
      GST_QUARK (NEW_BASE_TIME), G_TYPE_BOOLEAN, new_base_time, NULL);
  message = gst_message_new_custom (GST_MESSAGE_ASYNC_START, src, structure);

  return message;
}

/**
 * gst_message_new_async_done:
 * @src: The object originating the message.
 *
 * The message is posted when elements completed an ASYNC state change.
 *
 * Returns: The new async_done message.
 *
 * MT safe.
 *
 * Since: 0.10.13
 */
GstMessage *
gst_message_new_async_done (GstObject * src)
{
  GstMessage *message;

  message = gst_message_new_custom (GST_MESSAGE_ASYNC_DONE, src, NULL);

  return message;
}

/**
 * gst_message_new_latency:
 * @src: The object originating the message.
 *
 * This message can be posted by elements when their latency requirements have
 * changed.
 *
 * Returns: The new latency message. 
 *
 * MT safe.
 *
 * Since: 0.10.12
 */
GstMessage *
gst_message_new_latency (GstObject * src)
{
  GstMessage *message;

  message = gst_message_new_custom (GST_MESSAGE_LATENCY, src, NULL);

  return message;
}

/**
 * gst_message_new_request_state:
 * @src: The object originating the message.
 * @state: The new requested state
 *
 * This message can be posted by elements when they want to have their state
 * changed. A typical use case would be an audio server that wants to pause the
 * pipeline because a higher priority stream is being played.
 *
 * Returns: The new requst state message. 
 *
 * MT safe.
 *
 * Since: 0.10.23
 */
GstMessage *
gst_message_new_request_state (GstObject * src, GstState state)
{
  GstMessage *message;
  GstStructure *structure;

  structure = gst_structure_empty_new ("GstMessageRequestState");
  gst_structure_id_set (structure,
      GST_QUARK (NEW_STATE), GST_TYPE_STATE, (gint) state, NULL);
  message = gst_message_new_custom (GST_MESSAGE_REQUEST_STATE, src, structure);

  return message;
}

/**
 * gst_message_get_structure:
 * @message: The #GstMessage.
 *
 * Access the structure of the message.
 *
 * Returns: The structure of the message. The structure is still
 * owned by the message, which means that you should not free it and
 * that the pointer becomes invalid when you free the message.
 *
 * MT safe.
 */
const GstStructure *
gst_message_get_structure (GstMessage * message)
{
  g_return_val_if_fail (GST_IS_MESSAGE (message), NULL);

  return message->structure;
}

/**
 * gst_message_parse_tag:
 * @message: A valid #GstMessage of type GST_MESSAGE_TAG.
 * @tag_list: Return location for the tag-list.
 *
 * Extracts the tag list from the GstMessage. The tag list returned in the
 * output argument is a copy; the caller must free it when done.
 *
 * MT safe.
 */
void
gst_message_parse_tag (GstMessage * message, GstTagList ** tag_list)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_TAG);
  g_return_if_fail (tag_list != NULL);

  *tag_list = (GstTagList *) gst_structure_copy (message->structure);
}

/**
 * gst_message_parse_buffering:
 * @message: A valid #GstMessage of type GST_MESSAGE_BUFFERING.
 * @percent: Return location for the percent.
 *
 * Extracts the buffering percent from the GstMessage. see also
 * gst_message_new_buffering().
 *
 * Since: 0.10.11
 *
 * MT safe.
 */
void
gst_message_parse_buffering (GstMessage * message, gint * percent)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_BUFFERING);

  if (percent)
    *percent = g_value_get_int (gst_structure_id_get_value (message->structure,
            GST_QUARK (BUFFER_PERCENT)));
}

/**
 * gst_message_set_buffering_stats:
 * @message: A valid #GstMessage of type GST_MESSAGE_BUFFERING.
 * @mode: a buffering mode 
 * @avg_in: the average input rate
 * @avg_out: the average output rate
 * @buffering_left: amount of buffering time left in milliseconds
 *
 * Configures the buffering stats values in @message.
 *
 * Since: 0.10.20
 */
void
gst_message_set_buffering_stats (GstMessage * message, GstBufferingMode mode,
    gint avg_in, gint avg_out, gint64 buffering_left)
{
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_BUFFERING);

  gst_structure_id_set (message->structure,
      GST_QUARK (BUFFERING_MODE), GST_TYPE_BUFFERING_MODE, mode,
      GST_QUARK (AVG_IN_RATE), G_TYPE_INT, avg_in,
      GST_QUARK (AVG_OUT_RATE), G_TYPE_INT, avg_out,
      GST_QUARK (BUFFERING_LEFT), G_TYPE_INT64, buffering_left, NULL);
}

/**
 * gst_message_parse_buffering_stats:
 * @message: A valid #GstMessage of type GST_MESSAGE_BUFFERING.
 * @mode: a buffering mode 
 * @avg_in: the average input rate
 * @avg_out: the average output rate
 * @buffering_left: amount of buffering time left in milliseconds.
 *
 * Extracts the buffering stats values from @message.
 *
 * Since: 0.10.20
 */
void
gst_message_parse_buffering_stats (GstMessage * message,
    GstBufferingMode * mode, gint * avg_in, gint * avg_out,
    gint64 * buffering_left)
{
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_BUFFERING);

  if (mode)
    *mode = g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (BUFFERING_MODE)));
  if (avg_in)
    *avg_in = g_value_get_int (gst_structure_id_get_value (message->structure,
            GST_QUARK (AVG_IN_RATE)));
  if (avg_out)
    *avg_out = g_value_get_int (gst_structure_id_get_value (message->structure,
            GST_QUARK (AVG_OUT_RATE)));
  if (buffering_left)
    *buffering_left =
        g_value_get_int64 (gst_structure_id_get_value (message->structure,
            GST_QUARK (BUFFERING_LEFT)));
}

/**
 * gst_message_parse_state_changed:
 * @message: a valid #GstMessage of type GST_MESSAGE_STATE_CHANGED
 * @oldstate: the previous state, or NULL
 * @newstate: the new (current) state, or NULL
 * @pending: the pending (target) state, or NULL
 *
 * Extracts the old and new states from the GstMessage.
 *
 * MT safe.
 */
void
gst_message_parse_state_changed (GstMessage * message,
    GstState * oldstate, GstState * newstate, GstState * pending)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_STATE_CHANGED);

  if (oldstate)
    *oldstate =
        g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (OLD_STATE)));
  if (newstate)
    *newstate =
        g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (NEW_STATE)));
  if (pending)
    *pending = g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (PENDING_STATE)));
}

/**
 * gst_message_parse_clock_provide:
 * @message: A valid #GstMessage of type GST_MESSAGE_CLOCK_PROVIDE.
 * @clock: A pointer to  hold a clock object.
 * @ready: A pointer to hold the ready flag.
 *
 * Extracts the clock and ready flag from the GstMessage.
 * The clock object returned remains valid until the message is freed.
 *
 * MT safe.
 */
void
gst_message_parse_clock_provide (GstMessage * message, GstClock ** clock,
    gboolean * ready)
{
  const GValue *clock_gvalue;

  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_CLOCK_PROVIDE);

  clock_gvalue =
      gst_structure_id_get_value (message->structure, GST_QUARK (CLOCK));
  g_return_if_fail (clock_gvalue != NULL);
  g_return_if_fail (G_VALUE_TYPE (clock_gvalue) == GST_TYPE_CLOCK);

  if (ready)
    *ready =
        g_value_get_boolean (gst_structure_id_get_value (message->structure,
            GST_QUARK (READY)));
  if (clock)
    *clock = (GstClock *) g_value_get_object (clock_gvalue);
}

/**
 * gst_message_parse_clock_lost:
 * @message: A valid #GstMessage of type GST_MESSAGE_CLOCK_LOST.
 * @clock: A pointer to hold the lost clock
 *
 * Extracts the lost clock from the GstMessage.
 * The clock object returned remains valid until the message is freed.
 *
 * MT safe.
 */
void
gst_message_parse_clock_lost (GstMessage * message, GstClock ** clock)
{
  const GValue *clock_gvalue;

  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_CLOCK_LOST);

  clock_gvalue =
      gst_structure_id_get_value (message->structure, GST_QUARK (CLOCK));
  g_return_if_fail (clock_gvalue != NULL);
  g_return_if_fail (G_VALUE_TYPE (clock_gvalue) == GST_TYPE_CLOCK);

  if (clock)
    *clock = (GstClock *) g_value_get_object (clock_gvalue);
}

/**
 * gst_message_parse_new_clock:
 * @message: A valid #GstMessage of type GST_MESSAGE_NEW_CLOCK.
 * @clock: A pointer to hold the selected new clock
 *
 * Extracts the new clock from the GstMessage.
 * The clock object returned remains valid until the message is freed.
 *
 * MT safe.
 */
void
gst_message_parse_new_clock (GstMessage * message, GstClock ** clock)
{
  const GValue *clock_gvalue;

  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_NEW_CLOCK);

  clock_gvalue =
      gst_structure_id_get_value (message->structure, GST_QUARK (CLOCK));
  g_return_if_fail (clock_gvalue != NULL);
  g_return_if_fail (G_VALUE_TYPE (clock_gvalue) == GST_TYPE_CLOCK);

  if (clock)
    *clock = (GstClock *) g_value_get_object (clock_gvalue);
}

/**
 * gst_message_parse_structure_change:
 * @message: A valid #GstMessage of type GST_MESSAGE_STRUCTURE_CHANGE.
 * @type: A pointer to hold the change type
 * @owner: The owner element of the message source
 * @busy: A pointer to hold whether the change is in progress or has been
 * completed
 *
 * Extracts the change type and completion status from the GstMessage.
 *
 * MT safe.
 *
 * Since: 0.10.22
 */
void
gst_message_parse_structure_change (GstMessage * message,
    GstStructureChangeType * type, GstElement ** owner, gboolean * busy)
{
  const GValue *owner_gvalue;

  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_STRUCTURE_CHANGE);

  owner_gvalue =
      gst_structure_id_get_value (message->structure, GST_QUARK (OWNER));
  g_return_if_fail (owner_gvalue != NULL);
  g_return_if_fail (G_VALUE_TYPE (owner_gvalue) == GST_TYPE_ELEMENT);

  if (type)
    *type = g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (TYPE)));
  if (owner)
    *owner = (GstElement *) g_value_get_object (owner_gvalue);
  if (busy)
    *busy =
        g_value_get_boolean (gst_structure_id_get_value (message->structure,
            GST_QUARK (BUSY)));
}

/**
 * gst_message_parse_error:
 * @message: A valid #GstMessage of type GST_MESSAGE_ERROR.
 * @gerror: Location for the GError
 * @debug: Location for the debug message, or NULL
 *
 * Extracts the GError and debug string from the GstMessage. The values returned
 * in the output arguments are copies; the caller must free them when done.
 *
 * MT safe.
 */
void
gst_message_parse_error (GstMessage * message, GError ** gerror, gchar ** debug)
{
  const GValue *error_gvalue;
  GError *error_val;

  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_ERROR);

  error_gvalue =
      gst_structure_id_get_value (message->structure, GST_QUARK (GERROR));
  g_return_if_fail (error_gvalue != NULL);
  g_return_if_fail (G_VALUE_TYPE (error_gvalue) == GST_TYPE_G_ERROR);

  error_val = (GError *) g_value_get_boxed (error_gvalue);
  if (error_val)
    *gerror = g_error_copy (error_val);
  else
    *gerror = NULL;

  if (debug)
    *debug =
        g_value_dup_string (gst_structure_id_get_value (message->structure,
            GST_QUARK (DEBUG)));
}

/**
 * gst_message_parse_warning:
 * @message: A valid #GstMessage of type GST_MESSAGE_WARNING.
 * @gerror: Location for the GError
 * @debug: Location for the debug message, or NULL
 *
 * Extracts the GError and debug string from the GstMessage. The values returned
 * in the output arguments are copies; the caller must free them when done.
 *
 * MT safe.
 */
void
gst_message_parse_warning (GstMessage * message, GError ** gerror,
    gchar ** debug)
{
  const GValue *error_gvalue;
  GError *error_val;

  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_WARNING);

  error_gvalue =
      gst_structure_id_get_value (message->structure, GST_QUARK (GERROR));
  g_return_if_fail (error_gvalue != NULL);
  g_return_if_fail (G_VALUE_TYPE (error_gvalue) == GST_TYPE_G_ERROR);

  error_val = (GError *) g_value_get_boxed (error_gvalue);
  if (error_val)
    *gerror = g_error_copy (error_val);
  else
    *gerror = NULL;

  if (debug)
    *debug =
        g_value_dup_string (gst_structure_id_get_value (message->structure,
            GST_QUARK (DEBUG)));
}

/**
 * gst_message_parse_info:
 * @message: A valid #GstMessage of type GST_MESSAGE_INFO.
 * @gerror: Location for the GError
 * @debug: Location for the debug message, or NULL
 *
 * Extracts the GError and debug string from the GstMessage. The values returned
 * in the output arguments are copies; the caller must free them when done.
 *
 * MT safe.
 *
 * Since: 0.10.12
 */
void
gst_message_parse_info (GstMessage * message, GError ** gerror, gchar ** debug)
{
  const GValue *error_gvalue;
  GError *error_val;

  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_INFO);

  error_gvalue =
      gst_structure_id_get_value (message->structure, GST_QUARK (GERROR));
  g_return_if_fail (error_gvalue != NULL);
  g_return_if_fail (G_VALUE_TYPE (error_gvalue) == GST_TYPE_G_ERROR);

  error_val = (GError *) g_value_get_boxed (error_gvalue);
  if (error_val)
    *gerror = g_error_copy (error_val);
  else
    *gerror = NULL;

  if (debug)
    *debug =
        g_value_dup_string (gst_structure_id_get_value (message->structure,
            GST_QUARK (DEBUG)));
}

/**
 * gst_message_parse_segment_start:
 * @message: A valid #GstMessage of type GST_MESSAGE_SEGMENT_START.
 * @format: Result location for the format, or NULL
 * @position: Result location for the position, or NULL
 *
 * Extracts the position and format from the segment start message.
 *
 * MT safe.
 */
void
gst_message_parse_segment_start (GstMessage * message, GstFormat * format,
    gint64 * position)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_SEGMENT_START);

  if (format)
    *format =
        g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (FORMAT)));
  if (position)
    *position =
        g_value_get_int64 (gst_structure_id_get_value (message->structure,
            GST_QUARK (POSITION)));
}

/**
 * gst_message_parse_segment_done:
 * @message: A valid #GstMessage of type GST_MESSAGE_SEGMENT_DONE.
 * @format: Result location for the format, or NULL
 * @position: Result location for the position, or NULL
 *
 * Extracts the position and format from the segment start message.
 *
 * MT safe.
 */
void
gst_message_parse_segment_done (GstMessage * message, GstFormat * format,
    gint64 * position)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_SEGMENT_DONE);

  if (format)
    *format =
        g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (FORMAT)));
  if (position)
    *position =
        g_value_get_int64 (gst_structure_id_get_value (message->structure,
            GST_QUARK (POSITION)));
}

/**
 * gst_message_parse_duration:
 * @message: A valid #GstMessage of type GST_MESSAGE_DURATION.
 * @format: Result location for the format, or NULL
 * @duration: Result location for the duration, or NULL
 *
 * Extracts the duration and format from the duration message. The duration
 * might be GST_CLOCK_TIME_NONE, which indicates that the duration has
 * changed. Applications should always use a query to retrieve the duration
 * of a pipeline.
 *
 * MT safe.
 */
void
gst_message_parse_duration (GstMessage * message, GstFormat * format,
    gint64 * duration)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_DURATION);

  if (format)
    *format =
        g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (FORMAT)));
  if (duration)
    *duration =
        g_value_get_int64 (gst_structure_id_get_value (message->structure,
            GST_QUARK (DURATION)));
}

/**
 * gst_message_parse_async_start:
 * @message: A valid #GstMessage of type GST_MESSAGE_ASYNC_DONE.
 * @new_base_time: Result location for the new_base_time or NULL
 *
 * Extract the new_base_time from the async_start message. 
 *
 * MT safe.
 *
 * Since: 0.10.13
 */
void
gst_message_parse_async_start (GstMessage * message, gboolean * new_base_time)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_ASYNC_START);

  if (new_base_time)
    *new_base_time =
        g_value_get_boolean (gst_structure_id_get_value (message->structure,
            GST_QUARK (NEW_BASE_TIME)));
}

/**
 * gst_message_parse_request_state:
 * @message: A valid #GstMessage of type GST_MESSAGE_REQUEST_STATE.
 * @state: Result location for the requested state or NULL
 *
 * Extract the requested state from the request_state message.
 *
 * MT safe.
 *
 * Since: 0.10.23
 */
void
gst_message_parse_request_state (GstMessage * message, GstState * state)
{
  g_return_if_fail (GST_IS_MESSAGE (message));
  g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_REQUEST_STATE);

  if (state)
    *state = g_value_get_enum (gst_structure_id_get_value (message->structure,
            GST_QUARK (NEW_STATE)));
}