gstreamer/gst/timecode/gsttimecodewait.c

/*
 * GStreamer
 * Copyright (C) 2016 Vivia Nikolaidou <vivia@toolsonair.com>
 *
 * Based on gstvideoframe-audiolevel.c:
 * Copyright (C) 2015 Vivia Nikolaidou <vivia@toolsonair.com>
 *
 * 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., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

/**
 * SECTION:element-timecodewait
 *
 * This element acts like a synchronized audio/video "level". It gathers
 * all audio buffers sent between two video frames, and then sends a message
 * that contains the RMS value of all samples for these buffers.
 *
 * <refsect2>
 * <title>Example launch line</title>
 * |[
 * gst-launch-1.0 filesrc location="my_file" ! decodebin name=d ! "audio/x-raw" ! timecodewait name=l target-timecode-str="00:00:04:00" ! autoaudiosink d. ! "video/x-raw" ! timecodestamper ! l. l. ! queue ! timeoverlay time-mode=time-code ! autovideosink
 * </refsect2>
 */

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

#include "gsttimecodewait.h"

#define GST_CAT_DEFAULT gst_timecodewait_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);

static GstStaticPadTemplate audio_sink_template =
GST_STATIC_PAD_TEMPLATE ("asink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("audio/x-raw")
    );

static GstStaticPadTemplate audio_src_template =
GST_STATIC_PAD_TEMPLATE ("asrc",
    GST_PAD_SRC,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("audio/x-raw")
    );

static GstStaticPadTemplate video_sink_template =
GST_STATIC_PAD_TEMPLATE ("vsink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("video/x-raw")
    );

static GstStaticPadTemplate video_src_template =
GST_STATIC_PAD_TEMPLATE ("vsrc",
    GST_PAD_SRC,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("video/x-raw")
    );

#define parent_class gst_timecodewait_parent_class
G_DEFINE_TYPE (GstTimeCodeWait, gst_timecodewait, GST_TYPE_ELEMENT);

enum
{
  PROP_0,
  PROP_TARGET_TIME_CODE,
  PROP_TARGET_TIME_CODE_STRING
};

#define DEFAULT_TARGET_TIMECODE_STR "00:00:00:00"

static void gst_timecodewait_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec);
static void gst_timecodewait_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec);

static GstFlowReturn gst_timecodewait_asink_chain (GstPad * pad,
    GstObject * parent, GstBuffer * inbuf);
static GstFlowReturn gst_timecodewait_vsink_chain (GstPad * pad,
    GstObject * parent, GstBuffer * inbuf);
static gboolean gst_timecodewait_asink_event (GstPad * pad,
    GstObject * parent, GstEvent * event);
static gboolean gst_timecodewait_vsink_event (GstPad * pad,
    GstObject * parent, GstEvent * event);
static GstIterator *gst_timecodewait_iterate_internal_links (GstPad *
    pad, GstObject * parent);

static void gst_timecodewait_finalize (GObject * gobject);

static GstStateChangeReturn gst_timecodewait_change_state (GstElement *
    element, GstStateChange transition);

static void
gst_timecodewait_class_init (GstTimeCodeWaitClass * klass)
{
  GstElementClass *gstelement_class;
  GObjectClass *gobject_class = (GObjectClass *) klass;

  GST_DEBUG_CATEGORY_INIT (gst_timecodewait_debug,
      "timecodewait", 0, "timecodewait");

  gstelement_class = (GstElementClass *) klass;

  gst_element_class_set_static_metadata (gstelement_class,
      "Timecode Wait", "Filter/Audio/Video",
      "Drops all audio/video until a specific timecode has been reached",
      "Vivia Nikolaidou <vivia@toolsonair.com>");

  gobject_class->set_property = gst_timecodewait_set_property;
  gobject_class->get_property = gst_timecodewait_get_property;

  g_object_class_install_property (gobject_class, PROP_TARGET_TIME_CODE_STRING,
      g_param_spec_string ("target-timecode-string", "Target timecode (string)",
          "Timecode to wait for (string). Must take the form 00:00:00:00",
          DEFAULT_TARGET_TIMECODE_STR,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));

  g_object_class_install_property (gobject_class, PROP_TARGET_TIME_CODE,
      g_param_spec_boxed ("target-timecode", "Target timecode (object)",
          "Timecode to wait for (object)",
          GST_TYPE_VIDEO_TIME_CODE,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));

  gobject_class->finalize = gst_timecodewait_finalize;
  gstelement_class->change_state = gst_timecodewait_change_state;

  gst_element_class_add_static_pad_template (gstelement_class,
      &audio_src_template);
  gst_element_class_add_static_pad_template (gstelement_class,
      &audio_sink_template);

  gst_element_class_add_static_pad_template (gstelement_class,
      &video_src_template);
  gst_element_class_add_static_pad_template (gstelement_class,
      &video_sink_template);
}

static void
gst_timecodewait_init (GstTimeCodeWait * self)
{
  self->asinkpad =
      gst_pad_new_from_static_template (&audio_sink_template, "asink");
  gst_pad_set_chain_function (self->asinkpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_asink_chain));
  gst_pad_set_event_function (self->asinkpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_asink_event));
  gst_pad_set_iterate_internal_links_function (self->asinkpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_iterate_internal_links));
  gst_element_add_pad (GST_ELEMENT (self), self->asinkpad);

  self->vsinkpad =
      gst_pad_new_from_static_template (&video_sink_template, "vsink");
  gst_pad_set_chain_function (self->vsinkpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_vsink_chain));
  gst_pad_set_event_function (self->vsinkpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_vsink_event));
  gst_pad_set_iterate_internal_links_function (self->vsinkpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_iterate_internal_links));
  gst_element_add_pad (GST_ELEMENT (self), self->vsinkpad);

  self->asrcpad =
      gst_pad_new_from_static_template (&audio_src_template, "asrc");
  gst_pad_set_iterate_internal_links_function (self->asrcpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_iterate_internal_links));
  gst_element_add_pad (GST_ELEMENT (self), self->asrcpad);

  self->vsrcpad =
      gst_pad_new_from_static_template (&video_src_template, "vsrc");
  gst_pad_set_iterate_internal_links_function (self->vsrcpad,
      GST_DEBUG_FUNCPTR (gst_timecodewait_iterate_internal_links));
  gst_element_add_pad (GST_ELEMENT (self), self->vsrcpad);

  GST_PAD_SET_PROXY_CAPS (self->asinkpad);
  GST_PAD_SET_PROXY_ALLOCATION (self->asinkpad);

  GST_PAD_SET_PROXY_CAPS (self->asrcpad);
  GST_PAD_SET_PROXY_SCHEDULING (self->asrcpad);

  GST_PAD_SET_PROXY_CAPS (self->vsinkpad);
  GST_PAD_SET_PROXY_ALLOCATION (self->vsinkpad);

  GST_PAD_SET_PROXY_CAPS (self->vsrcpad);
  GST_PAD_SET_PROXY_SCHEDULING (self->vsrcpad);

  self->running_time_of_timecode = GST_CLOCK_TIME_NONE;

  self->video_eos_flag = FALSE;
  self->audio_flush_flag = FALSE;
  self->shutdown_flag = FALSE;
  self->from_string = FALSE;
  self->tc = gst_video_time_code_new_empty ();

  g_mutex_init (&self->mutex);
  g_cond_init (&self->cond);
}

static GstStateChangeReturn
gst_timecodewait_change_state (GstElement * element, GstStateChange transition)
{
  GstStateChangeReturn ret;
  GstTimeCodeWait *self = GST_TIMECODEWAIT (element);

  switch (transition) {
    case GST_STATE_CHANGE_PAUSED_TO_READY:
      g_mutex_lock (&self->mutex);
      self->shutdown_flag = TRUE;
      g_cond_signal (&self->cond);
      g_mutex_unlock (&self->mutex);
      break;
    case GST_STATE_CHANGE_READY_TO_PAUSED:
      g_mutex_lock (&self->mutex);
      self->shutdown_flag = FALSE;
      self->video_eos_flag = FALSE;
      self->audio_flush_flag = FALSE;
      g_mutex_unlock (&self->mutex);
    default:
      break;
  }

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

  switch (transition) {
    case GST_STATE_CHANGE_PAUSED_TO_READY:
      g_mutex_lock (&self->mutex);
      self->running_time_of_timecode = GST_CLOCK_TIME_NONE;
      gst_segment_init (&self->asegment, GST_FORMAT_UNDEFINED);
      self->asegment.position = GST_CLOCK_TIME_NONE;
      gst_segment_init (&self->vsegment, GST_FORMAT_UNDEFINED);
      self->vsegment.position = GST_CLOCK_TIME_NONE;
      g_mutex_unlock (&self->mutex);
      break;
    default:
      break;
  }

  return ret;
}

static void
gst_timecodewait_finalize (GObject * object)
{
  GstTimeCodeWait *self = GST_TIMECODEWAIT (object);

  if (self->tc) {
    gst_video_time_code_free (self->tc);
    self->tc = NULL;
  }

  g_mutex_clear (&self->mutex);
  g_cond_clear (&self->cond);

  G_OBJECT_CLASS (parent_class)->finalize (object);
}

static void
gst_timecodewait_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec)
{
  GstTimeCodeWait *self = GST_TIMECODEWAIT (object);

  switch (prop_id) {
    case PROP_TARGET_TIME_CODE_STRING:{
      if (self->tc)
        g_value_take_string (value, gst_video_time_code_to_string (self->tc));
      else
        g_value_set_string (value, DEFAULT_TARGET_TIMECODE_STR);
      break;
    }
    case PROP_TARGET_TIME_CODE:{
      g_value_set_boxed (value, self->tc);
      break;
    }
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_timecodewait_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  GstTimeCodeWait *self = GST_TIMECODEWAIT (object);

  switch (prop_id) {
    case PROP_TARGET_TIME_CODE_STRING:{
      gchar **parts;
      const gchar *tc_str;
      guint hours, minutes, seconds, frames;

      tc_str = g_value_get_string (value);
      parts = g_strsplit (tc_str, ":", 4);
      if (!parts || parts[3] == NULL) {
        GST_ERROR_OBJECT (self,
            "Error: Could not parse timecode %s. Please input a timecode in the form 00:00:00:00",
            tc_str);
        g_strfreev (parts);
        return;
      }
      hours = g_ascii_strtoll (parts[0], NULL, 10);
      minutes = g_ascii_strtoll (parts[1], NULL, 10);
      seconds = g_ascii_strtoll (parts[2], NULL, 10);
      frames = g_ascii_strtoll (parts[3], NULL, 10);
      gst_video_time_code_init (self->tc, 0, 1, NULL, 0, hours, minutes,
          seconds, frames, 0);
      if (self->vinfo.finfo != NULL) {
        self->tc->config.fps_n = self->vinfo.fps_n;
        self->tc->config.fps_d = self->vinfo.fps_d;
      }
      self->from_string = TRUE;
      g_strfreev (parts);
      break;
    }
    case PROP_TARGET_TIME_CODE:{
      if (self->tc)
        gst_video_time_code_free (self->tc);
      self->tc = g_value_dup_boxed (value);
      self->from_string = FALSE;
      break;
    }
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static gboolean
gst_timecodewait_vsink_event (GstPad * pad, GstObject * parent,
    GstEvent * event)
{
  GstTimeCodeWait *self = GST_TIMECODEWAIT (parent);
  GST_LOG_OBJECT (pad, "Got %s event", GST_EVENT_TYPE_NAME (event));

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_SEGMENT:
      g_mutex_lock (&self->mutex);
      gst_event_copy_segment (event, &self->vsegment);
      if (self->vsegment.format != GST_FORMAT_TIME) {
        GST_ERROR_OBJECT (self, "Invalid segment format");
        g_mutex_unlock (&self->mutex);
        gst_event_unref (event);
        return FALSE;
      }
      self->vsegment.position = GST_CLOCK_TIME_NONE;
      g_mutex_unlock (&self->mutex);
      break;
    case GST_EVENT_GAP:
      gst_event_unref (event);
      return TRUE;
    case GST_EVENT_EOS:
      g_mutex_lock (&self->mutex);
      self->video_eos_flag = TRUE;
      g_cond_signal (&self->cond);
      g_mutex_unlock (&self->mutex);
      break;
    case GST_EVENT_FLUSH_START:
      g_mutex_lock (&self->mutex);
      gst_segment_init (&self->vsegment, GST_FORMAT_UNDEFINED);
      g_cond_signal (&self->cond);
      g_mutex_unlock (&self->mutex);
      self->vsegment.position = GST_CLOCK_TIME_NONE;
      break;
    case GST_EVENT_CAPS:{
      GstCaps *caps;
      gst_event_parse_caps (event, &caps);
      GST_DEBUG_OBJECT (self, "Got caps %" GST_PTR_FORMAT, caps);
      if (!gst_video_info_from_caps (&self->vinfo, caps)) {
        gst_event_unref (event);
        return FALSE;
      }
      g_mutex_lock (&self->mutex);
      if (self->from_string) {
        self->tc->config.fps_n = self->vinfo.fps_n;
        self->tc->config.fps_d = self->vinfo.fps_d;
      }
      g_mutex_unlock (&self->mutex);
      break;
    }
    default:
      break;
  }
  return gst_pad_event_default (pad, parent, event);
}

static gboolean
gst_timecodewait_asink_event (GstPad * pad, GstObject * parent,
    GstEvent * event)
{
  GstTimeCodeWait *self = GST_TIMECODEWAIT (parent);
  GST_LOG_OBJECT (pad, "Got %s event", GST_EVENT_TYPE_NAME (event));

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_SEGMENT:
      g_mutex_lock (&self->mutex);
      self->running_time_of_timecode = GST_CLOCK_TIME_NONE;
      gst_event_copy_segment (event, &self->asegment);
      if (self->asegment.format != GST_FORMAT_TIME) {
        GST_ERROR_OBJECT (self, "Invalid segment format");
        g_mutex_unlock (&self->mutex);
        return FALSE;
      }
      self->asegment.position = GST_CLOCK_TIME_NONE;
      g_mutex_unlock (&self->mutex);
      break;
    case GST_EVENT_FLUSH_START:
      g_mutex_lock (&self->mutex);
      self->audio_flush_flag = TRUE;
      g_cond_signal (&self->cond);
      g_mutex_unlock (&self->mutex);
      break;
    case GST_EVENT_FLUSH_STOP:
      g_mutex_lock (&self->mutex);
      self->audio_flush_flag = FALSE;
      self->running_time_of_timecode = GST_CLOCK_TIME_NONE;
      gst_segment_init (&self->asegment, GST_FORMAT_UNDEFINED);
      self->asegment.position = GST_CLOCK_TIME_NONE;
      g_mutex_unlock (&self->mutex);
      break;
    case GST_EVENT_CAPS:{
      GstCaps *caps;
      gst_event_parse_caps (event, &caps);
      GST_DEBUG_OBJECT (self, "Got caps %" GST_PTR_FORMAT, caps);
      g_mutex_lock (&self->mutex);
      if (!gst_audio_info_from_caps (&self->ainfo, caps)) {
        g_mutex_unlock (&self->mutex);
        return FALSE;
      }
      self->running_time_of_timecode = GST_CLOCK_TIME_NONE;
      g_mutex_unlock (&self->mutex);
      break;
    }
    default:
      break;
  }

  return gst_pad_event_default (pad, parent, event);
}

static GstFlowReturn
gst_timecodewait_vsink_chain (GstPad * pad, GstObject * parent,
    GstBuffer * inbuf)
{
  GstClockTime timestamp;
  GstTimeCodeWait *self = GST_TIMECODEWAIT (parent);
  GstClockTime duration;
  GstVideoTimeCode *tc = NULL;
  GstVideoTimeCodeMeta *tc_meta;

  timestamp = GST_BUFFER_TIMESTAMP (inbuf);
  if (timestamp == GST_CLOCK_TIME_NONE) {
    gst_buffer_unref (inbuf);
    return GST_FLOW_ERROR;
  }
  g_mutex_lock (&self->mutex);
  self->vsegment.position = timestamp;
  duration = GST_BUFFER_DURATION (inbuf);
  if (duration != GST_CLOCK_TIME_NONE)
    self->vsegment.position += duration;
  tc_meta = gst_buffer_get_video_time_code_meta (inbuf);
  if (tc_meta)
    tc = &tc_meta->tc;
  if (self->tc != NULL && tc != NULL) {
    if (gst_video_time_code_compare (tc, self->tc) < 0
        && self->running_time_of_timecode == GST_CLOCK_TIME_NONE) {
      GST_DEBUG_OBJECT (self, "Timecode not yet reached, ignoring frame");
      gst_buffer_unref (inbuf);
      inbuf = NULL;
    } else if (self->running_time_of_timecode == GST_CLOCK_TIME_NONE) {
      GST_INFO_OBJECT (self, "Target timecode reached at %" GST_TIME_FORMAT,
          GST_TIME_ARGS (self->vsegment.position));
      self->running_time_of_timecode =
          gst_segment_to_running_time (&self->vsegment, GST_FORMAT_TIME,
          self->vsegment.position);
    }
  }
  g_cond_signal (&self->cond);
  g_mutex_unlock (&self->mutex);
  if (inbuf)
    return gst_pad_push (self->vsrcpad, inbuf);
  else
    return GST_FLOW_OK;
}

/*
 * assumes sign1 and sign2 are either 1 or -1
 * returns 0 if sign1*num1 == sign2*num2
 * -1 if sign1*num1 < sign2*num2
 *  1 if sign1*num1 > sign2*num2
 */
static gint
gst_timecodewait_compare_guint64_with_signs (gint sign1,
    guint64 num1, gint sign2, guint64 num2)
{
  if (sign1 != sign2)
    return sign1;
  else if (num1 == num2)
    return 0;
  else
    return num1 > num2 ? sign1 : -sign1;
}

static GstFlowReturn
gst_timecodewait_asink_chain (GstPad * pad, GstObject * parent,
    GstBuffer * inbuf)
{
  GstClockTime timestamp;
  GstTimeCodeWait *self = GST_TIMECODEWAIT (parent);
  GstClockTime current_running_time;
  GstClockTime video_running_time = GST_CLOCK_TIME_NONE;
  GstClockTime duration;
  GstClockTime running_time_at_end = GST_CLOCK_TIME_NONE;
  gint asign, vsign = 1, esign = 1;

  timestamp = GST_BUFFER_TIMESTAMP (inbuf);
  if (timestamp == GST_CLOCK_TIME_NONE) {
    gst_buffer_unref (inbuf);
    return GST_FLOW_ERROR;
  }
  g_mutex_lock (&self->mutex);
  self->asegment.position = timestamp;
  asign =
      gst_segment_to_running_time_full (&self->asegment, GST_FORMAT_TIME,
      self->asegment.position, &current_running_time);
  if (asign == 0) {
    g_mutex_unlock (&self->mutex);
    gst_buffer_unref (inbuf);
    GST_ERROR_OBJECT (self, "Could not get current running time");
    return GST_FLOW_ERROR;
  }
  if (self->vsegment.format == GST_FORMAT_TIME) {
    vsign =
        gst_segment_to_running_time_full (&self->vsegment, GST_FORMAT_TIME,
        self->vsegment.position, &video_running_time);
    if (vsign == 0) {
      video_running_time = GST_CLOCK_TIME_NONE;
    }
  }
  while (!(self->video_eos_flag || self->audio_flush_flag
          || self->shutdown_flag) && (video_running_time == GST_CLOCK_TIME_NONE
          || gst_timecodewait_compare_guint64_with_signs (asign,
              current_running_time, vsign, video_running_time) == 1)
      && self->running_time_of_timecode == GST_CLOCK_TIME_NONE) {
    g_cond_wait (&self->cond, &self->mutex);
    vsign =
        gst_segment_to_running_time_full (&self->vsegment, GST_FORMAT_TIME,
        self->vsegment.position, &video_running_time);
    if (vsign == 0) {
      video_running_time = GST_CLOCK_TIME_NONE;
    }
  }
  if (self->audio_flush_flag || self->shutdown_flag) {
    GST_DEBUG_OBJECT (self, "Shutting down, ignoring frame");
    gst_buffer_unref (inbuf);
    return GST_FLOW_FLUSHING;
  }
  duration = GST_BUFFER_DURATION (inbuf);
  if (duration != GST_CLOCK_TIME_NONE) {
    esign =
        gst_segment_to_running_time_full (&self->asegment, GST_FORMAT_TIME,
        self->asegment.position + duration, &running_time_at_end);
    if (esign == 0) {
      g_mutex_unlock (&self->mutex);
      GST_ERROR_OBJECT (self, "Could not get running time at end");
      gst_buffer_unref (inbuf);
      return GST_FLOW_ERROR;
    }
  }
  if (self->running_time_of_timecode == GST_CLOCK_TIME_NONE
      || gst_timecodewait_compare_guint64_with_signs (esign,
          running_time_at_end, 1, self->running_time_of_timecode) == -1) {
    GST_DEBUG_OBJECT (self,
        "Dropped an audio buf at %" GST_TIME_FORMAT " with timecode %"
        GST_TIME_FORMAT " video timecode %" GST_TIME_FORMAT,
        GST_TIME_ARGS (current_running_time),
        GST_TIME_ARGS (self->running_time_of_timecode),
        GST_TIME_ARGS (video_running_time));
    gst_buffer_unref (inbuf);
    inbuf = NULL;
  } else if (current_running_time < self->running_time_of_timecode
      && running_time_at_end > self->running_time_of_timecode) {
    GstSegment asegment2 = self->asegment;

    gst_segment_set_running_time (&asegment2, GST_FORMAT_TIME,
        self->running_time_of_timecode);
    inbuf =
        gst_audio_buffer_clip (inbuf, &asegment2, self->ainfo.rate,
        self->ainfo.bpf);
  }
  g_mutex_unlock (&self->mutex);
  if (inbuf)
    return gst_pad_push (self->asrcpad, inbuf);
  else
    return GST_FLOW_OK;
}

static GstIterator *
gst_timecodewait_iterate_internal_links (GstPad * pad, GstObject * parent)
{
  GstIterator *it = NULL;
  GstPad *opad;
  GValue val = G_VALUE_INIT;
  GstTimeCodeWait *self = GST_TIMECODEWAIT (parent);

  if (self->asinkpad == pad)
    opad = gst_object_ref (self->asrcpad);
  else if (self->asrcpad == pad)
    opad = gst_object_ref (self->asinkpad);
  else if (self->vsinkpad == pad)
    opad = gst_object_ref (self->vsrcpad);
  else if (self->vsrcpad == pad)
    opad = gst_object_ref (self->vsinkpad);
  else
    goto out;

  g_value_init (&val, GST_TYPE_PAD);
  g_value_set_object (&val, opad);
  it = gst_iterator_new_single (GST_TYPE_PAD, &val);
  g_value_unset (&val);

  gst_object_unref (opad);

out:
  return it;
}