plugins/elements/gsttypefindelement.c

/* GStreamer
 * Copyright (C) 2003 Benjamin Otte <in7y118@public.uni-hamburg.de>
 *
 * gsttypefindelement.c: element that detects type of stream
 *
 * 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.
 */

/* FIXME: need a better solution for non-seekable streams */

/* way of operation:
 * 1) get a list of all typefind functions sorted best to worst
 * 2) if all elements have been called with all requested data goto 8
 * 3) call all functions once with all available data
 * 4) if a function returns a value >= ARG_MAXIMUM goto 8
 * 5) all functions with a result > ARG_MINIMUM or functions that did not get
 *    all requested data (where peek returned NULL) stay in list
 * 6) seek to requested offset of best function that still has open data
 *    requests
 * 7) goto 2
 * 8) take best available result and use its caps
 *
 * The element has two scheduling modes:
 *
 * 1) chain based, it will collect buffers and run the typefind function on
 *    the buffer until something is found.
 * 2) getrange based, it will proxy the getrange function to the sinkpad. It
 *    is assumed that the peer element is happy with whatever format we
 *    eventually read.
 *
 * When the element has no connected srcpad, and the sinkpad can operate in
 * getrange based mode, the element starts its own task to figure out the
 * type of the stream.
 *
 */

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

#include "gsttypefindelement.h"
#include "gst/gst_private.h"
#include "gst/gst-i18n-lib.h"
#include "gst/base/gsttypefindhelper.h"

#include <gst/gsttypefind.h>
#include <gst/gstutils.h>
#include <gst/gsterror.h>

GST_DEBUG_CATEGORY_STATIC (gst_type_find_element_debug);
#define GST_CAT_DEFAULT gst_type_find_element_debug

static const GstElementDetails gst_type_find_element_details =
GST_ELEMENT_DETAILS ("TypeFind",
    "Generic",
    "Finds the media type of a stream",
    "Benjamin Otte <in7y118@public.uni-hamburg.de>");

/* generic templates */
GstStaticPadTemplate type_find_element_sink_template =
GST_STATIC_PAD_TEMPLATE ("sink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS_ANY);

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

/* Require at least 2kB of data before we attempt typefinding in chain-mode.
 * 128kB is massive overkill for the maximum, but doesn't do any harm */
#define TYPE_FIND_MIN_SIZE   (2*1024)
#define TYPE_FIND_MAX_SIZE (128*1024)

/* TypeFind signals and args */
enum
{
  HAVE_TYPE,
  LAST_SIGNAL
};
enum
{
  ARG_0,
  ARG_CAPS,
  ARG_MINIMUM,
  ARG_MAXIMUM
};
enum
{
  MODE_NORMAL,                  /* act as identity */
  MODE_TYPEFIND,                /* do typefinding  */
  MODE_ERROR                    /* had fatal error */
};


#define _do_init(bla) \
    GST_DEBUG_CATEGORY_INIT (gst_type_find_element_debug, "typefind",           \
        GST_DEBUG_BG_YELLOW | GST_DEBUG_FG_GREEN, "type finding element");

GST_BOILERPLATE_FULL (GstTypeFindElement, gst_type_find_element, GstElement,
    GST_TYPE_ELEMENT, _do_init);

static void gst_type_find_element_dispose (GObject * object);
static void gst_type_find_element_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec);
static void gst_type_find_element_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec);

#if 0
static const GstEventMask *gst_type_find_element_src_event_mask (GstPad * pad);
#endif

static gboolean gst_type_find_element_src_event (GstPad * pad,
    GstEvent * event);
static gboolean gst_type_find_handle_src_query (GstPad * pad, GstQuery * query);

static gboolean gst_type_find_element_handle_event (GstPad * pad,
    GstEvent * event);
static GstFlowReturn gst_type_find_element_chain (GstPad * sinkpad,
    GstBuffer * buffer);
static GstFlowReturn gst_type_find_element_getrange (GstPad * srcpad,
    guint64 offset, guint length, GstBuffer ** buffer);
static gboolean gst_type_find_element_checkgetrange (GstPad * srcpad);

static GstStateChangeReturn
gst_type_find_element_change_state (GstElement * element,
    GstStateChange transition);
static gboolean gst_type_find_element_activate (GstPad * pad);
static gboolean
gst_type_find_element_activate_src_pull (GstPad * pad, gboolean active);
static GstFlowReturn
gst_type_find_element_chain_do_typefinding (GstTypeFindElement * typefind);
static void
gst_type_find_element_send_cached_events (GstTypeFindElement * typefind);

static guint gst_type_find_element_signals[LAST_SIGNAL] = { 0 };

static void
gst_type_find_element_have_type (GstTypeFindElement * typefind,
    guint probability, const GstCaps * caps)
{
  g_assert (typefind->caps == NULL);
  g_assert (caps != NULL);

  GST_INFO_OBJECT (typefind, "found caps %" GST_PTR_FORMAT, caps);
  typefind->caps = gst_caps_copy (caps);
  gst_pad_set_caps (typefind->src, (GstCaps *) caps);
}

static void
gst_type_find_element_base_init (gpointer g_class)
{
  GstElementClass *gstelement_class = GST_ELEMENT_CLASS (g_class);

  gst_element_class_add_pad_template (gstelement_class,
      gst_static_pad_template_get (&type_find_element_src_template));
  gst_element_class_add_pad_template (gstelement_class,
      gst_static_pad_template_get (&type_find_element_sink_template));
  gst_element_class_set_details (gstelement_class,
      &gst_type_find_element_details);
}
static void
gst_type_find_element_class_init (GstTypeFindElementClass * typefind_class)
{
  GObjectClass *gobject_class = G_OBJECT_CLASS (typefind_class);
  GstElementClass *gstelement_class = GST_ELEMENT_CLASS (typefind_class);

  gobject_class->set_property =
      GST_DEBUG_FUNCPTR (gst_type_find_element_set_property);
  gobject_class->get_property =
      GST_DEBUG_FUNCPTR (gst_type_find_element_get_property);
  gobject_class->dispose = GST_DEBUG_FUNCPTR (gst_type_find_element_dispose);

  typefind_class->have_type = gst_type_find_element_have_type;

  g_object_class_install_property (gobject_class, ARG_CAPS,
      g_param_spec_boxed ("caps", _("caps"),
          _("detected capabilities in stream"), gst_caps_get_type (),
          G_PARAM_READABLE));
  g_object_class_install_property (gobject_class, ARG_MINIMUM,
      g_param_spec_uint ("minimum", _("minimum"),
          "minimum probability required to accept caps", GST_TYPE_FIND_MINIMUM,
          GST_TYPE_FIND_MAXIMUM, GST_TYPE_FIND_MINIMUM, G_PARAM_READWRITE));
  g_object_class_install_property (gobject_class, ARG_MAXIMUM,
      g_param_spec_uint ("maximum", _("maximum"),
          "probability to stop typefinding (deprecated; non-functional)",
          GST_TYPE_FIND_MINIMUM, GST_TYPE_FIND_MAXIMUM, GST_TYPE_FIND_MAXIMUM,
          G_PARAM_READWRITE));
  /**
   * GstTypeFindElement::have-type:
   * @typefind: the typefind instance
   * @probability: the probability of the type found
   * @caps: the caps of the type found
   *
   * This signal gets emitted when the type and its probability has 
   * been found.
   */
  gst_type_find_element_signals[HAVE_TYPE] = g_signal_new ("have_type",
      G_TYPE_FROM_CLASS (typefind_class), G_SIGNAL_RUN_FIRST,
      G_STRUCT_OFFSET (GstTypeFindElementClass, have_type), NULL, NULL,
      gst_marshal_VOID__UINT_BOXED, G_TYPE_NONE, 2,
      G_TYPE_UINT, GST_TYPE_CAPS | G_SIGNAL_TYPE_STATIC_SCOPE);

  gstelement_class->change_state =
      GST_DEBUG_FUNCPTR (gst_type_find_element_change_state);
}
static void
gst_type_find_element_init (GstTypeFindElement * typefind,
    GstTypeFindElementClass * g_class)
{
  /* sinkpad */
  typefind->sink =
      gst_pad_new_from_static_template (&type_find_element_sink_template,
      "sink");

  gst_pad_set_activate_function (typefind->sink,
      GST_DEBUG_FUNCPTR (gst_type_find_element_activate));
  gst_pad_set_chain_function (typefind->sink,
      GST_DEBUG_FUNCPTR (gst_type_find_element_chain));
  gst_pad_set_event_function (typefind->sink,
      GST_DEBUG_FUNCPTR (gst_type_find_element_handle_event));
  gst_element_add_pad (GST_ELEMENT (typefind), typefind->sink);

  /* srcpad */
  typefind->src =
      gst_pad_new_from_static_template (&type_find_element_src_template, "src");

  gst_pad_set_activatepull_function (typefind->src,
      GST_DEBUG_FUNCPTR (gst_type_find_element_activate_src_pull));
  gst_pad_set_checkgetrange_function (typefind->src,
      GST_DEBUG_FUNCPTR (gst_type_find_element_checkgetrange));
  gst_pad_set_getrange_function (typefind->src,
      GST_DEBUG_FUNCPTR (gst_type_find_element_getrange));
  gst_pad_set_event_function (typefind->src,
      GST_DEBUG_FUNCPTR (gst_type_find_element_src_event));
  gst_pad_set_query_function (typefind->src,
      GST_DEBUG_FUNCPTR (gst_type_find_handle_src_query));
  gst_pad_use_fixed_caps (typefind->src);
  gst_element_add_pad (GST_ELEMENT (typefind), typefind->src);

  typefind->mode = MODE_TYPEFIND;
  typefind->caps = NULL;
  typefind->min_probability = 1;
  typefind->max_probability = GST_TYPE_FIND_MAXIMUM;

  typefind->store = NULL;
}
static void
gst_type_find_element_dispose (GObject * object)
{
  GstTypeFindElement *typefind = GST_TYPE_FIND_ELEMENT (object);

  G_OBJECT_CLASS (parent_class)->dispose (object);

  if (typefind->store) {
    gst_buffer_unref (typefind->store);
    typefind->store = NULL;
  }
}
static void
gst_type_find_element_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  GstTypeFindElement *typefind;

  typefind = GST_TYPE_FIND_ELEMENT (object);

  switch (prop_id) {
    case ARG_MINIMUM:
      typefind->min_probability = g_value_get_uint (value);
      break;
    case ARG_MAXIMUM:
      typefind->max_probability = g_value_get_uint (value);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}
static void
gst_type_find_element_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec)
{
  GstTypeFindElement *typefind;

  typefind = GST_TYPE_FIND_ELEMENT (object);

  switch (prop_id) {
    case ARG_CAPS:
      g_value_set_boxed (value, typefind->caps);
      break;
    case ARG_MINIMUM:
      g_value_set_uint (value, typefind->min_probability);
      break;
    case ARG_MAXIMUM:
      g_value_set_uint (value, typefind->max_probability);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static gboolean
gst_type_find_handle_src_query (GstPad * pad, GstQuery * query)
{
  GstTypeFindElement *typefind;
  gboolean res = FALSE;
  GstPad *peer;

  typefind = GST_TYPE_FIND_ELEMENT (GST_PAD_PARENT (pad));

  peer = gst_pad_get_peer (typefind->sink);
  if (peer == NULL)
    return FALSE;

  res = gst_pad_query (peer, query);
  if (!res)
    goto out;

  switch (GST_QUERY_TYPE (query)) {
    case GST_QUERY_POSITION:
    {
      gint64 peer_pos;
      GstFormat format;

      if (typefind->store == NULL)
        goto out;

      gst_query_parse_position (query, &format, &peer_pos);

      /* FIXME: this code assumes that there's no discont in the queue */
      switch (format) {
        case GST_FORMAT_BYTES:
          peer_pos -= typefind->store->size;
          break;
        default:
          /* FIXME */
          break;
      }
      gst_query_set_position (query, format, peer_pos);
      break;
    }
    default:
      break;
  }

out:
  gst_object_unref (peer);
  return res;
}

#if 0
static const GstEventMask *
gst_type_find_element_src_event_mask (GstPad * pad)
{
  static const GstEventMask mask[] = {
    {GST_EVENT_SEEK,
        GST_SEEK_METHOD_SET | GST_SEEK_METHOD_CUR | GST_SEEK_METHOD_END |
          GST_SEEK_FLAG_FLUSH},
    /* add more if you want, event masks suck and need to die anyway */
    {0,}
  };

  return mask;
}
#endif

static gboolean
gst_type_find_element_src_event (GstPad * pad, GstEvent * event)
{
  GstTypeFindElement *typefind = GST_TYPE_FIND_ELEMENT (GST_PAD_PARENT (pad));

  if (typefind->mode != MODE_NORMAL) {
    /* need to do more? */
    gst_mini_object_unref (GST_MINI_OBJECT (event));
    return FALSE;
  }
  return gst_pad_event_default (pad, event);
}

static void
start_typefinding (GstTypeFindElement * typefind)
{
  GST_DEBUG_OBJECT (typefind, "starting typefinding");
  gst_pad_set_caps (typefind->src, NULL);
  if (typefind->caps) {
    gst_caps_replace (&typefind->caps, NULL);
  }
  typefind->mode = MODE_TYPEFIND;
}

static void
stop_typefinding (GstTypeFindElement * typefind)
{
  GstState state;
  gboolean push_cached_buffers;

  gst_element_get_state (GST_ELEMENT (typefind), &state, NULL, 0);

  push_cached_buffers = (state >= GST_STATE_PAUSED);

  GST_DEBUG_OBJECT (typefind, "stopping typefinding%s",
      push_cached_buffers ? " and pushing cached buffers" : "");

  if (typefind->store) {
    if (!push_cached_buffers) {
      gst_buffer_unref (typefind->store);
    } else {
      GstPad *peer = gst_pad_get_peer (typefind->src);

      typefind->mode = MODE_NORMAL;
      gst_buffer_set_caps (typefind->store, typefind->caps);

      /* make sure the user gets a meaningful error message in this case,
       * which is not a core bug or bug of any kind (as the default error
       * message emitted by gstpad.c otherwise would make you think) */
      if (peer && GST_PAD_CHAINFUNC (peer) == NULL) {
        GST_DEBUG_OBJECT (typefind, "upstream only supports push mode, while "
            "downstream element only works in pull mode, erroring out");
        GST_ELEMENT_ERROR (typefind, STREAM, FAILED,
            ("%s cannot work in push mode. The operation is not supported "
                "with this source element or protocol.",
                G_OBJECT_TYPE_NAME (GST_PAD_PARENT (peer))),
            ("Downstream pad %s:%s has no chainfunction, and the upstream "
                "element does not support pull mode",
                GST_DEBUG_PAD_NAME (peer)));
        typefind->mode = MODE_ERROR;    /* make the chain function error out */
      } else {
        gst_type_find_element_send_cached_events (typefind);
        gst_pad_push (typefind->src, typefind->store);
      }

      if (peer)
        gst_object_unref (peer);
    }
    typefind->store = NULL;
  }
}

static gboolean
gst_type_find_element_handle_event (GstPad * pad, GstEvent * event)
{
  gboolean res = FALSE;
  GstTypeFindElement *typefind = GST_TYPE_FIND_ELEMENT (GST_PAD_PARENT (pad));

  GST_DEBUG_OBJECT (typefind, "got %s event in mode %d",
      GST_EVENT_TYPE_NAME (event), typefind->mode);

  switch (typefind->mode) {
    case MODE_TYPEFIND:
      switch (GST_EVENT_TYPE (event)) {
        case GST_EVENT_EOS:{
          GstTypeFindProbability prob = 0;
          GstCaps *caps = NULL;
          gboolean found = FALSE;

          GST_INFO_OBJECT (typefind, "Got EOS and no type found yet");

          /* we might not have started typefinding yet because there was not
           * enough data so far; just give it a shot now and see what we get */
          if (typefind->store) {
            caps = gst_type_find_helper_for_buffer (GST_OBJECT (typefind),
                typefind->store, &prob);

            if (caps && prob >= typefind->min_probability) {
              g_signal_emit (typefind, gst_type_find_element_signals[HAVE_TYPE],
                  0, prob, caps);
              found = TRUE;
            }
            gst_caps_replace (&caps, NULL);
          }

          if (!found) {
            GST_ELEMENT_ERROR (typefind, STREAM, TYPE_NOT_FOUND,
                (NULL), (NULL));
          }

          stop_typefinding (typefind);
          res = gst_pad_event_default (pad, event);
          break;
        }
        default:
          GST_DEBUG_OBJECT (typefind, "Saving %s event to send later",
              GST_EVENT_TYPE_NAME (event));
          typefind->cached_events =
              g_list_append (typefind->cached_events, event);
          res = TRUE;
          break;
      }
      break;
    case MODE_NORMAL:
      res = gst_pad_event_default (pad, event);
      break;
    case MODE_ERROR:
      break;
    default:
      g_assert_not_reached ();
  }
  return res;
}

static void
gst_type_find_element_send_cached_events (GstTypeFindElement * typefind)
{
  GList *l;

  for (l = typefind->cached_events; l != NULL; l = l->next) {
    GstEvent *event = GST_EVENT (l->data);

    GST_DEBUG_OBJECT (typefind, "sending cached %s event",
        GST_EVENT_TYPE_NAME (event));
    gst_pad_push_event (typefind->src, event);
  }
  g_list_free (typefind->cached_events);
  typefind->cached_events = NULL;
}

static GstFlowReturn
gst_type_find_element_chain (GstPad * pad, GstBuffer * buffer)
{
  GstTypeFindElement *typefind;
  GstFlowReturn res = GST_FLOW_OK;

  typefind = GST_TYPE_FIND_ELEMENT (GST_PAD_PARENT (pad));

  /* Shortcircuit typefinding if we already have non-any caps */
  if (typefind->mode == MODE_TYPEFIND) {
    const GstCaps *caps = GST_BUFFER_CAPS (buffer);

    if (caps && !gst_caps_is_any (caps)) {
      GST_DEBUG_OBJECT (typefind, "Skipping typefinding, using caps from "
          "upstream buffer: %" GST_PTR_FORMAT, caps);
      typefind->mode = MODE_NORMAL;
      g_signal_emit (typefind, gst_type_find_element_signals[HAVE_TYPE], 0,
          GST_TYPE_FIND_MAXIMUM, caps);

      gst_type_find_element_send_cached_events (typefind);
      if (typefind->store) {
        GST_DEBUG_OBJECT (typefind, "Pushing store: %d",
            GST_BUFFER_SIZE (typefind->store));
        gst_buffer_set_caps (typefind->store, typefind->caps);
        gst_pad_push (typefind->src, typefind->store);
        typefind->store = NULL;
      }
    }
  }

  switch (typefind->mode) {
    case MODE_ERROR:
      /* we should already have called GST_ELEMENT_ERROR */
      return GST_FLOW_ERROR;
    case MODE_NORMAL:
      gst_buffer_set_caps (buffer, typefind->caps);
      return gst_pad_push (typefind->src, buffer);
    case MODE_TYPEFIND:{
      if (typefind->store)
        typefind->store = gst_buffer_join (typefind->store, buffer);
      else
        typefind->store = buffer;

      res = gst_type_find_element_chain_do_typefinding (typefind);

      if (typefind->mode == MODE_ERROR)
        res = GST_FLOW_ERROR;

      break;
    }
    default:
      g_assert_not_reached ();
      return GST_FLOW_ERROR;
  }

  return res;
}

static GstFlowReturn
gst_type_find_element_chain_do_typefinding (GstTypeFindElement * typefind)
{
  GstTypeFindProbability probability;
  GstCaps *caps;

  if (GST_BUFFER_SIZE (typefind->store) < TYPE_FIND_MIN_SIZE) {
    GST_DEBUG_OBJECT (typefind, "not enough data for typefinding yet "
        "(%u bytes)", GST_BUFFER_SIZE (typefind->store));
    return GST_FLOW_OK;
  }

  caps = gst_type_find_helper_for_buffer (GST_OBJECT (typefind),
      typefind->store, &probability);

  if (caps == NULL && GST_BUFFER_SIZE (typefind->store) > TYPE_FIND_MAX_SIZE) {
    GST_ELEMENT_ERROR (typefind, STREAM, TYPE_NOT_FOUND, (NULL), (NULL));
    stop_typefinding (typefind);
    return GST_FLOW_ERROR;
  } else if (caps == NULL) {
    GST_DEBUG_OBJECT (typefind, "no caps found with %u bytes of data, "
        "waiting for more data", GST_BUFFER_SIZE (typefind->store));
    return GST_FLOW_OK;
  }

  /* found a type */
  if (probability < typefind->min_probability) {
    GST_DEBUG_OBJECT (typefind, "found caps %" GST_PTR_FORMAT ", but "
        "probability is %u which is lower than the required minimum of %u",
        caps, probability, typefind->min_probability);

    if (GST_BUFFER_SIZE (typefind->store) >= TYPE_FIND_MAX_SIZE) {
      GST_ELEMENT_ERROR (typefind, STREAM, TYPE_NOT_FOUND, (NULL), (NULL));
      stop_typefinding (typefind);
      return GST_FLOW_ERROR;
    }

    GST_DEBUG_OBJECT (typefind, "waiting for more data to try again");
    return GST_FLOW_OK;
  }

  /* probability is good enough too, so let's make it known ... */
  g_signal_emit (typefind, gst_type_find_element_signals[HAVE_TYPE], 0,
      probability, caps);

  /* .. and send out the accumulated data */
  stop_typefinding (typefind);
  return GST_FLOW_OK;
}

static gboolean
gst_type_find_element_checkgetrange (GstPad * srcpad)
{
  GstTypeFindElement *typefind;

  typefind = GST_TYPE_FIND_ELEMENT (GST_PAD_PARENT (srcpad));

  return gst_pad_check_pull_range (typefind->sink);
}

static GstFlowReturn
gst_type_find_element_getrange (GstPad * srcpad,
    guint64 offset, guint length, GstBuffer ** buffer)
{
  GstTypeFindElement *typefind;
  GstFlowReturn ret;

  typefind = GST_TYPE_FIND_ELEMENT (GST_PAD_PARENT (srcpad));

  ret = gst_pad_pull_range (typefind->sink, offset, length, buffer);

  if (ret == GST_FLOW_OK && buffer && *buffer)
    gst_buffer_set_caps (*buffer, typefind->caps);

  return ret;
}

static gboolean
gst_type_find_element_activate_src_pull (GstPad * pad, gboolean active)
{
  GstTypeFindElement *typefind;

  typefind = GST_TYPE_FIND_ELEMENT (GST_OBJECT_PARENT (pad));

  return gst_pad_activate_pull (typefind->sink, active);
}

static gboolean
gst_type_find_element_activate (GstPad * pad)
{
  GstTypeFindProbability probability = 0;
  GstCaps *found_caps = NULL;
  GstTypeFindElement *typefind;

  typefind = GST_TYPE_FIND_ELEMENT (GST_OBJECT_PARENT (pad));

  /* 1. try to activate in pull mode. if not, switch to push and succeed.
     2. try to pull type find.
     3. deactivate pull mode.
     4. src pad might have been activated push by the state change. deactivate.
     5. if we didn't find any caps, fail.
     6. emit have-type; maybe the app connected the source pad to something.
     7. if the sink pad is activated, we are in pull mode. succeed.
     otherwise activate both pads in push mode and succeed.
   */

  /* 1 */
  if (!gst_pad_check_pull_range (pad) || !gst_pad_activate_pull (pad, TRUE)) {
    start_typefinding (typefind);
    return gst_pad_activate_push (pad, TRUE);
  }

  /* 2 */
  {
    GstPad *peer;

    peer = gst_pad_get_peer (pad);
    if (peer) {
      gint64 size;
      GstFormat format = GST_FORMAT_BYTES;

      if (!gst_pad_query_duration (peer, &format, &size)) {
        GST_WARNING_OBJECT (typefind, "Could not query upstream length!");
        return FALSE;
      }

      found_caps = gst_type_find_helper_get_range (GST_OBJECT (peer),
          (GstTypeFindHelperGetRangeFunction) (GST_PAD_GETRANGEFUNC (peer)),
          (guint64) size, &probability);

      gst_object_unref (peer);
    }
  }

  /* 3 */
  gst_pad_activate_pull (pad, FALSE);

  /* 4 */
  gst_pad_activate_push (typefind->src, FALSE);

  /* 5 */
  if (!found_caps || probability < typefind->min_probability) {
    GST_ELEMENT_ERROR (typefind, STREAM, TYPE_NOT_FOUND, (NULL), (NULL));
    gst_caps_replace (&found_caps, NULL);
    return FALSE;
  }

  /* 6 */
  g_signal_emit (typefind, gst_type_find_element_signals[HAVE_TYPE],
      0, probability, found_caps);
  gst_caps_unref (found_caps);
  typefind->mode = MODE_NORMAL;

  /* 7 */
  if (gst_pad_is_active (pad))
    return TRUE;
  else {
    gboolean ret;

    ret = gst_pad_activate_push (typefind->src, TRUE);
    ret &= gst_pad_activate_push (pad, TRUE);
    return ret;
  }
}

static GstStateChangeReturn
gst_type_find_element_change_state (GstElement * element,
    GstStateChange transition)
{
  GstStateChangeReturn ret;
  GstTypeFindElement *typefind;

  typefind = GST_TYPE_FIND_ELEMENT (element);


  ret = GST_ELEMENT_CLASS (parent_class)->change_state (element, transition);

  switch (transition) {
    case GST_STATE_CHANGE_PAUSED_TO_READY:
      gst_caps_replace (&typefind->caps, NULL);
      g_list_foreach (typefind->cached_events,
          (GFunc) gst_mini_object_unref, NULL);
      g_list_free (typefind->cached_events);
      typefind->cached_events = NULL;
      break;
    default:
      break;
  }

  return ret;
}