gstreamer/gst/playback/gststreamsynchronizer.c

/* GStreamer
 * Copyright (C) 2010 Sebastian Dröge <sebastian.droege@collabora.co.uk>
 *
 * 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.
 */

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

#include "gststreamsynchronizer.h"

GST_DEBUG_CATEGORY_STATIC (stream_synchronizer_debug);
#define GST_CAT_DEFAULT stream_synchronizer_debug

#define GST_STREAM_SYNCHRONIZER_LOCK(obj) G_STMT_START {                \
    GST_TRACE_OBJECT (obj,                                              \
                    "locking from thread %p",                           \
                    g_thread_self ());                                  \
    g_mutex_lock (&GST_STREAM_SYNCHRONIZER_CAST(obj)->lock);            \
    GST_TRACE_OBJECT (obj,                                              \
                    "locked from thread %p",                            \
                    g_thread_self ());                                  \
} G_STMT_END

#define GST_STREAM_SYNCHRONIZER_UNLOCK(obj) G_STMT_START {              \
    GST_TRACE_OBJECT (obj,                                              \
                    "unlocking from thread %p",                         \
                    g_thread_self ());                                  \
    g_mutex_unlock (&GST_STREAM_SYNCHRONIZER_CAST(obj)->lock);              \
} G_STMT_END

static GstStaticPadTemplate srctemplate = GST_STATIC_PAD_TEMPLATE ("src_%u",
    GST_PAD_SRC,
    GST_PAD_SOMETIMES,
    GST_STATIC_CAPS_ANY);
static GstStaticPadTemplate sinktemplate = GST_STATIC_PAD_TEMPLATE ("sink_%u",
    GST_PAD_SINK,
    GST_PAD_REQUEST,
    GST_STATIC_CAPS_ANY);

#define gst_stream_synchronizer_parent_class parent_class
G_DEFINE_TYPE (GstStreamSynchronizer, gst_stream_synchronizer,
    GST_TYPE_ELEMENT);

typedef struct
{
  GstStreamSynchronizer *transform;
  guint stream_number;
  GstPad *srcpad;
  GstPad *sinkpad;
  GstSegment segment;

  gboolean wait;                /* TRUE if waiting/blocking */
  gboolean new_stream;
  gboolean drop_discont;
  gboolean is_eos;              /* TRUE if EOS was received */
  gboolean seen_data;

  GCond stream_finish_cond;

  /* seqnum of the previously received STREAM_START
   * default: G_MAXUINT32 */
  guint32 stream_start_seqnum;
  guint32 segment_seqnum;
} GstStream;

/* Must be called with lock! */
static inline GstPad *
gst_stream_get_other_pad (GstStream * stream, GstPad * pad)
{
  if (stream->sinkpad == pad)
    return gst_object_ref (stream->srcpad);
  if (stream->srcpad == pad)
    return gst_object_ref (stream->sinkpad);

  return NULL;
}

static GstPad *
gst_stream_get_other_pad_from_pad (GstStreamSynchronizer * self, GstPad * pad)
{
  GstStream *stream;
  GstPad *opad = NULL;

  GST_STREAM_SYNCHRONIZER_LOCK (self);
  stream = gst_pad_get_element_private (pad);
  if (!stream)
    goto out;

  opad = gst_stream_get_other_pad (stream, pad);

out:
  GST_STREAM_SYNCHRONIZER_UNLOCK (self);

  if (!opad)
    GST_WARNING_OBJECT (pad, "Trying to get other pad after releasing");

  return opad;
}

/* Generic pad functions */
static GstIterator *
gst_stream_synchronizer_iterate_internal_links (GstPad * pad,
    GstObject * parent)
{
  GstIterator *it = NULL;
  GstPad *opad;

  opad =
      gst_stream_get_other_pad_from_pad (GST_STREAM_SYNCHRONIZER (parent), pad);
  if (opad) {
    GValue value = { 0, };

    g_value_init (&value, GST_TYPE_PAD);
    g_value_set_object (&value, opad);
    it = gst_iterator_new_single (GST_TYPE_PAD, &value);
    g_value_unset (&value);
    gst_object_unref (opad);
  }

  return it;
}

static gboolean
gst_stream_synchronizer_query (GstPad * pad, GstObject * parent,
    GstQuery * query)
{
  GstPad *opad;
  gboolean ret = FALSE;

  GST_LOG_OBJECT (pad, "Handling query %s", GST_QUERY_TYPE_NAME (query));

  opad =
      gst_stream_get_other_pad_from_pad (GST_STREAM_SYNCHRONIZER (parent), pad);
  if (opad) {
    ret = gst_pad_peer_query (opad, query);
    gst_object_unref (opad);
  }

  return ret;
}

/* srcpad functions */
static gboolean
gst_stream_synchronizer_src_event (GstPad * pad, GstObject * parent,
    GstEvent * event)
{
  GstStreamSynchronizer *self = GST_STREAM_SYNCHRONIZER (parent);
  GstPad *opad;
  gboolean ret = FALSE;

  GST_LOG_OBJECT (pad, "Handling event %s: %" GST_PTR_FORMAT,
      GST_EVENT_TYPE_NAME (event), event);

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_QOS:{
      gdouble proportion;
      GstClockTimeDiff diff;
      GstClockTime timestamp;
      gint64 running_time_diff = -1;
      GstStream *stream;

      gst_event_parse_qos (event, NULL, &proportion, &diff, &timestamp);
      gst_event_unref (event);

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      stream = gst_pad_get_element_private (pad);
      if (stream)
        running_time_diff = stream->segment.base;
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);

      if (running_time_diff == -1) {
        GST_WARNING_OBJECT (pad, "QOS event before group start");
        goto out;
      }
      if (timestamp < running_time_diff) {
        GST_DEBUG_OBJECT (pad, "QOS event from previous group");
        goto out;
      }

      GST_LOG_OBJECT (pad,
          "Adjusting QOS event: %" GST_TIME_FORMAT " - %" GST_TIME_FORMAT " = %"
          GST_TIME_FORMAT, GST_TIME_ARGS (timestamp),
          GST_TIME_ARGS (running_time_diff),
          GST_TIME_ARGS (timestamp - running_time_diff));

      timestamp -= running_time_diff;

      /* That case is invalid for QoS events */
      if (diff < 0 && -diff > timestamp) {
        GST_DEBUG_OBJECT (pad, "QOS event from previous group");
        ret = TRUE;
        goto out;
      }

      event =
          gst_event_new_qos (GST_QOS_TYPE_UNDERFLOW, proportion, diff,
          timestamp);
      break;
    }
    default:
      break;
  }

  opad = gst_stream_get_other_pad_from_pad (self, pad);
  if (opad) {
    ret = gst_pad_push_event (opad, event);
    gst_object_unref (opad);
  }

out:
  return ret;
}

/* sinkpad functions */
static gboolean
gst_stream_synchronizer_sink_event (GstPad * pad, GstObject * parent,
    GstEvent * event)
{
  GstStreamSynchronizer *self = GST_STREAM_SYNCHRONIZER (parent);
  GstPad *opad;
  gboolean ret = FALSE;

  GST_LOG_OBJECT (pad, "Handling event %s: %" GST_PTR_FORMAT,
      GST_EVENT_TYPE_NAME (event), event);

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_STREAM_START:
    {
      GstStream *stream, *ostream;
      guint32 seqnum = gst_event_get_seqnum (event);
      GList *l;
      gboolean all_wait = TRUE;
      gboolean new_stream = TRUE;

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      stream = gst_pad_get_element_private (pad);
      if (stream && stream->stream_start_seqnum != seqnum) {
        stream->is_eos = FALSE;
        stream->stream_start_seqnum = seqnum;
        stream->drop_discont = TRUE;

        /* Check if this belongs to a stream that is already there,
         * e.g. we got the visualizations for an audio stream */
        for (l = self->streams; l; l = l->next) {
          ostream = l->data;

          if (ostream != stream && ostream->stream_start_seqnum == seqnum
              && !ostream->wait) {
            new_stream = FALSE;
            break;
          }
        }

        if (!new_stream) {
          GST_DEBUG_OBJECT (pad,
              "Stream %d belongs to running stream %d, no waiting",
              stream->stream_number, ostream->stream_number);
          stream->wait = FALSE;
          stream->new_stream = FALSE;
        } else {
          GST_DEBUG_OBJECT (pad, "Stream %d changed", stream->stream_number);

          stream->wait = TRUE;
          stream->new_stream = TRUE;

          for (l = self->streams; l; l = l->next) {
            GstStream *ostream = l->data;

            all_wait = all_wait && ostream->wait;
            if (!all_wait)
              break;
          }
          if (all_wait) {
            gint64 position = 0;

            GST_DEBUG_OBJECT (self, "All streams have changed -- unblocking");

            for (l = self->streams; l; l = l->next) {
              GstStream *ostream = l->data;
              gint64 stop_running_time;
              gint64 position_running_time;

              ostream->wait = FALSE;

              if (ostream->segment.format == GST_FORMAT_TIME) {
                stop_running_time =
                    gst_segment_to_running_time (&ostream->segment,
                    GST_FORMAT_TIME, ostream->segment.stop);
                position_running_time =
                    gst_segment_to_running_time (&ostream->segment,
                    GST_FORMAT_TIME, ostream->segment.position);
                position =
                    MAX (position, MAX (stop_running_time,
                        position_running_time));
              }
            }
            position = MAX (0, position);
            self->group_start_time = MAX (self->group_start_time, position);

            GST_DEBUG_OBJECT (self, "New group start time: %" GST_TIME_FORMAT,
                GST_TIME_ARGS (self->group_start_time));

            for (l = self->streams; l; l = l->next) {
              GstStream *ostream = l->data;
              g_cond_broadcast (&ostream->stream_finish_cond);
            }
          }
        }
      } else {
        GST_DEBUG_OBJECT (self, "No stream or STREAM_START from same source");
      }

      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
      break;
    }
    case GST_EVENT_SEGMENT:{
      GstStream *stream;
      GstSegment segment;

      gst_event_copy_segment (event, &segment);

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      stream = gst_pad_get_element_private (pad);
      if (stream) {
        if (stream->wait) {
          GST_DEBUG_OBJECT (pad, "Stream %d is waiting", stream->stream_number);
          g_cond_wait (&stream->stream_finish_cond, &self->lock);
          stream = gst_pad_get_element_private (pad);
          if (stream)
            stream->wait = FALSE;
        }
      }

      if (self->shutdown) {
        GST_STREAM_SYNCHRONIZER_UNLOCK (self);
        gst_event_unref (event);
        goto done;
      }

      if (stream && segment.format == GST_FORMAT_TIME) {
        if (stream->new_stream) {
          stream->new_stream = FALSE;
          segment.base = self->group_start_time;
        }

        GST_DEBUG_OBJECT (pad, "Segment was: %" GST_SEGMENT_FORMAT,
            &stream->segment);
        gst_segment_copy_into (&segment, &stream->segment);
        GST_DEBUG_OBJECT (pad, "Segment now is: %" GST_SEGMENT_FORMAT,
            &stream->segment);
        stream->segment_seqnum = gst_event_get_seqnum (event);

        GST_DEBUG_OBJECT (pad, "Stream start running time: %" GST_TIME_FORMAT,
            GST_TIME_ARGS (stream->segment.base));
        {
          GstEvent *tmpev;

          tmpev = gst_event_new_segment (&stream->segment);
          gst_event_set_seqnum (tmpev, stream->segment_seqnum);
          gst_event_unref (event);
          event = tmpev;
        }
      } else if (stream) {
        GST_WARNING_OBJECT (pad, "Non-TIME segment: %s",
            gst_format_get_name (segment.format));
        gst_segment_init (&stream->segment, GST_FORMAT_UNDEFINED);
      }
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
      break;
    }
    case GST_EVENT_FLUSH_START:{
      GstStream *stream;

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      stream = gst_pad_get_element_private (pad);
      if (stream) {
        GST_DEBUG_OBJECT (pad, "Flushing streams");
        g_cond_broadcast (&stream->stream_finish_cond);
      }
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
      break;
    }
    case GST_EVENT_FLUSH_STOP:{
      GstStream *stream;

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      stream = gst_pad_get_element_private (pad);
      if (stream) {
        GST_DEBUG_OBJECT (pad, "Resetting segment for stream %d",
            stream->stream_number);
        gst_segment_init (&stream->segment, GST_FORMAT_UNDEFINED);

        stream->is_eos = FALSE;
        stream->wait = FALSE;
        stream->new_stream = FALSE;
        stream->drop_discont = FALSE;
        stream->seen_data = FALSE;
        g_cond_broadcast (&stream->stream_finish_cond);
      }
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
      break;
    }
    case GST_EVENT_EOS:{
      GstStream *stream;
      GList *l;
      gboolean all_eos = TRUE;
      gboolean seen_data;
      GSList *pads = NULL;
      GstPad *srcpad;
      GstClockTime timestamp;

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      stream = gst_pad_get_element_private (pad);
      if (!stream) {
        GST_STREAM_SYNCHRONIZER_UNLOCK (self);
        GST_WARNING_OBJECT (pad, "EOS for unknown stream");
        break;
      }

      GST_DEBUG_OBJECT (pad, "Have EOS for stream %d", stream->stream_number);
      stream->is_eos = TRUE;

      seen_data = stream->seen_data;
      srcpad = gst_object_ref (stream->srcpad);

      if (seen_data && stream->segment.position != -1)
        timestamp = stream->segment.position;
      else if (stream->segment.rate < 0.0 || stream->segment.stop == -1)
        timestamp = stream->segment.start;
      else
        timestamp = stream->segment.stop;

      for (l = self->streams; l; l = l->next) {
        GstStream *ostream = l->data;

        all_eos = all_eos && ostream->is_eos;
        if (!all_eos)
          break;
      }

      if (all_eos) {
        GST_DEBUG_OBJECT (self, "All streams are EOS -- forwarding");
        for (l = self->streams; l; l = l->next) {
          GstStream *ostream = l->data;
          /* local snapshot of current pads */
          gst_object_ref (ostream->srcpad);
          pads = g_slist_prepend (pads, ostream->srcpad);
        }
      }
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
      /* drop lock when sending eos, which may block in e.g. preroll */
      if (pads) {
        GstPad *pad;
        GSList *epad;

        ret = TRUE;
        epad = pads;
        while (epad) {
          pad = epad->data;
          GST_DEBUG_OBJECT (pad, "Pushing EOS");
          ret = ret && gst_pad_push_event (pad, gst_event_new_eos ());
          gst_object_unref (pad);
          epad = g_slist_next (epad);
        }
        g_slist_free (pads);
      } else {
        /* if EOS, but no data has passed, then send something to replace EOS
         * for preroll purposes */
        if (!seen_data) {
          GstEvent *gap_event;

          gap_event = gst_event_new_gap (timestamp, GST_CLOCK_TIME_NONE);
          ret = gst_pad_push_event (srcpad, gap_event);
        } else {
          GstEvent *gap_event;

          /* FIXME: Also send a GAP event to let audio sinks start their
           * clock in case they did not have enough data yet */
          gap_event = gst_event_new_gap (timestamp, GST_CLOCK_TIME_NONE);
          ret = gst_pad_push_event (srcpad, gap_event);
        }
      }
      gst_object_unref (srcpad);
      gst_event_unref (event);
      goto done;
    }
    default:
      break;
  }

  opad = gst_stream_get_other_pad_from_pad (self, pad);
  if (opad) {
    ret = gst_pad_push_event (opad, event);
    gst_object_unref (opad);
  }

done:

  return ret;
}

static GstFlowReturn
gst_stream_synchronizer_sink_chain (GstPad * pad, GstObject * parent,
    GstBuffer * buffer)
{
  GstStreamSynchronizer *self = GST_STREAM_SYNCHRONIZER (parent);
  GstPad *opad;
  GstFlowReturn ret = GST_FLOW_ERROR;
  GstStream *stream;
  GstClockTime duration = GST_CLOCK_TIME_NONE;
  GstClockTime timestamp = GST_CLOCK_TIME_NONE;
  GstClockTime timestamp_end = GST_CLOCK_TIME_NONE;

  GST_LOG_OBJECT (pad, "Handling buffer %p: size=%" G_GSIZE_FORMAT
      ", timestamp=%" GST_TIME_FORMAT " duration=%" GST_TIME_FORMAT
      " offset=%" G_GUINT64_FORMAT " offset_end=%" G_GUINT64_FORMAT,
      buffer, gst_buffer_get_size (buffer),
      GST_TIME_ARGS (GST_BUFFER_TIMESTAMP (buffer)),
      GST_TIME_ARGS (GST_BUFFER_DURATION (buffer)),
      GST_BUFFER_OFFSET (buffer), GST_BUFFER_OFFSET_END (buffer));

  timestamp = GST_BUFFER_TIMESTAMP (buffer);
  duration = GST_BUFFER_DURATION (buffer);
  if (GST_CLOCK_TIME_IS_VALID (timestamp)
      && GST_CLOCK_TIME_IS_VALID (duration))
    timestamp_end = timestamp + duration;

  GST_STREAM_SYNCHRONIZER_LOCK (self);
  stream = gst_pad_get_element_private (pad);

  if (stream) {
    stream->seen_data = TRUE;
    if (stream->drop_discont) {
      if (GST_BUFFER_IS_DISCONT (buffer)) {
        GST_DEBUG_OBJECT (pad, "removing DISCONT from buffer %p", buffer);
        buffer = gst_buffer_make_writable (buffer);
        GST_BUFFER_FLAG_UNSET (buffer, GST_BUFFER_FLAG_DISCONT);
      }
      stream->drop_discont = FALSE;
    }

    if (stream->segment.format == GST_FORMAT_TIME
        && GST_CLOCK_TIME_IS_VALID (timestamp)) {
      GST_LOG_OBJECT (pad,
          "Updating position from %" GST_TIME_FORMAT " to %" GST_TIME_FORMAT,
          GST_TIME_ARGS (stream->segment.position), GST_TIME_ARGS (timestamp));
      if (stream->segment.rate > 0.0)
        stream->segment.position = timestamp;
      else
        stream->segment.position = timestamp_end;
    }
  }
  GST_STREAM_SYNCHRONIZER_UNLOCK (self);

  opad = gst_stream_get_other_pad_from_pad (self, pad);
  if (opad) {
    ret = gst_pad_push (opad, buffer);
    gst_object_unref (opad);
  }

  GST_LOG_OBJECT (pad, "Push returned: %s", gst_flow_get_name (ret));
  if (ret == GST_FLOW_OK) {
    GList *l;

    GST_STREAM_SYNCHRONIZER_LOCK (self);
    stream = gst_pad_get_element_private (pad);
    if (stream && stream->segment.format == GST_FORMAT_TIME) {
      GstClockTime position;

      if (stream->segment.rate > 0.0)
        position = timestamp_end;
      else
        position = timestamp;

      if (GST_CLOCK_TIME_IS_VALID (position)) {
        GST_LOG_OBJECT (pad,
            "Updating position from %" GST_TIME_FORMAT " to %" GST_TIME_FORMAT,
            GST_TIME_ARGS (stream->segment.position), GST_TIME_ARGS (position));
        stream->segment.position = position;
      }
    }

    /* Advance EOS streams if necessary. For non-EOS
     * streams the demuxers should already do this! */
    if (!GST_CLOCK_TIME_IS_VALID (timestamp_end) &&
        GST_CLOCK_TIME_IS_VALID (timestamp)) {
      timestamp_end = timestamp + GST_SECOND;
    }

    for (l = self->streams; l; l = l->next) {
      GstStream *ostream = l->data;
      gint64 position;

      if (!ostream->is_eos || ostream->segment.format != GST_FORMAT_TIME)
        continue;

      if (ostream->segment.position != -1)
        position = ostream->segment.position;
      else
        position = ostream->segment.start;

      /* Is there a 1 second lag? */
      if (position != -1 && GST_CLOCK_TIME_IS_VALID (timestamp_end) &&
          position + GST_SECOND < timestamp_end) {
        gint64 new_start;

        new_start = timestamp_end - GST_SECOND;

        GST_DEBUG_OBJECT (ostream->sinkpad,
            "Advancing stream %u from %" GST_TIME_FORMAT " to %"
            GST_TIME_FORMAT, ostream->stream_number, GST_TIME_ARGS (position),
            GST_TIME_ARGS (new_start));

        ostream->segment.position = new_start;

        gst_pad_push_event (ostream->srcpad,
            gst_event_new_gap (position, new_start - position));
      }
    }
    GST_STREAM_SYNCHRONIZER_UNLOCK (self);
  }

  return ret;
}

/* GstElement vfuncs */
static GstPad *
gst_stream_synchronizer_request_new_pad (GstElement * element,
    GstPadTemplate * temp, const gchar * name, const GstCaps * caps)
{
  GstStreamSynchronizer *self = GST_STREAM_SYNCHRONIZER (element);
  GstStream *stream;
  gchar *tmp;

  GST_STREAM_SYNCHRONIZER_LOCK (self);
  GST_DEBUG_OBJECT (self, "Requesting new pad for stream %d",
      self->current_stream_number);

  stream = g_slice_new0 (GstStream);
  stream->transform = self;
  stream->stream_number = self->current_stream_number;
  g_cond_init (&stream->stream_finish_cond);
  stream->stream_start_seqnum = G_MAXUINT32;
  stream->segment_seqnum = G_MAXUINT32;

  tmp = g_strdup_printf ("sink_%u", self->current_stream_number);
  stream->sinkpad = gst_pad_new_from_static_template (&sinktemplate, tmp);
  g_free (tmp);
  gst_pad_set_element_private (stream->sinkpad, stream);
  gst_pad_set_iterate_internal_links_function (stream->sinkpad,
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_iterate_internal_links));
  gst_pad_set_query_function (stream->sinkpad,
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_query));
  gst_pad_set_event_function (stream->sinkpad,
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_sink_event));
  gst_pad_set_chain_function (stream->sinkpad,
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_sink_chain));

  tmp = g_strdup_printf ("src_%u", self->current_stream_number);
  stream->srcpad = gst_pad_new_from_static_template (&srctemplate, tmp);
  g_free (tmp);
  gst_pad_set_element_private (stream->srcpad, stream);
  gst_pad_set_iterate_internal_links_function (stream->srcpad,
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_iterate_internal_links));
  gst_pad_set_query_function (stream->srcpad,
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_query));
  gst_pad_set_event_function (stream->srcpad,
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_src_event));

  gst_segment_init (&stream->segment, GST_FORMAT_UNDEFINED);

  self->streams = g_list_prepend (self->streams, stream);
  self->current_stream_number++;
  GST_STREAM_SYNCHRONIZER_UNLOCK (self);

  /* Add pads and activate unless we're going to NULL */
  g_rec_mutex_lock (GST_STATE_GET_LOCK (self));
  if (GST_STATE_TARGET (self) != GST_STATE_NULL) {
    gst_pad_set_active (stream->srcpad, TRUE);
    gst_pad_set_active (stream->sinkpad, TRUE);
  }
  gst_element_add_pad (GST_ELEMENT_CAST (self), stream->srcpad);
  gst_element_add_pad (GST_ELEMENT_CAST (self), stream->sinkpad);
  g_rec_mutex_unlock (GST_STATE_GET_LOCK (self));

  return stream->sinkpad;
}

/* Must be called with lock! */
static void
gst_stream_synchronizer_release_stream (GstStreamSynchronizer * self,
    GstStream * stream)
{
  GList *l;

  GST_DEBUG_OBJECT (self, "Releasing stream %d", stream->stream_number);

  for (l = self->streams; l; l = l->next) {
    if (l->data == stream) {
      self->streams = g_list_delete_link (self->streams, l);
      break;
    }
  }
  g_assert (l != NULL);

  /* we can drop the lock, since stream exists now only local.
   * Moreover, we should drop, to prevent deadlock with STREAM_LOCK
   * (due to reverse lock order) when deactivating pads */
  GST_STREAM_SYNCHRONIZER_UNLOCK (self);

  gst_pad_set_element_private (stream->srcpad, NULL);
  gst_pad_set_element_private (stream->sinkpad, NULL);
  gst_pad_set_active (stream->srcpad, FALSE);
  gst_element_remove_pad (GST_ELEMENT_CAST (self), stream->srcpad);
  gst_pad_set_active (stream->sinkpad, FALSE);
  gst_element_remove_pad (GST_ELEMENT_CAST (self), stream->sinkpad);

  if (stream->segment.format == GST_FORMAT_TIME) {
    gint64 stop_running_time;
    gint64 position_running_time;

    stop_running_time =
        gst_segment_to_running_time (&stream->segment, GST_FORMAT_TIME,
        stream->segment.stop);
    position_running_time =
        gst_segment_to_running_time (&stream->segment, GST_FORMAT_TIME,
        stream->segment.position);
    stop_running_time = MAX (stop_running_time, position_running_time);

    if (stop_running_time > self->group_start_time) {
      GST_DEBUG_OBJECT (stream->sinkpad,
          "Updating global start running time from %" GST_TIME_FORMAT " to %"
          GST_TIME_FORMAT, GST_TIME_ARGS (self->group_start_time),
          GST_TIME_ARGS (stop_running_time));

      self->group_start_time = stop_running_time;
    }
  }

  g_cond_clear (&stream->stream_finish_cond);
  g_slice_free (GstStream, stream);

  /* NOTE: In theory we have to check here if all streams
   * are EOS but the one that was removed wasn't and then
   * send EOS downstream. But due to the way how playsink
   * works this is not necessary and will only cause problems
   * for gapless playback. playsink will only add/remove pads
   * when it's reconfigured, which happens when the streams
   * change
   */

  /* lock for good measure, since the caller had it */
  GST_STREAM_SYNCHRONIZER_LOCK (self);
}

static void
gst_stream_synchronizer_release_pad (GstElement * element, GstPad * pad)
{
  GstStreamSynchronizer *self = GST_STREAM_SYNCHRONIZER (element);
  GstStream *stream;

  GST_STREAM_SYNCHRONIZER_LOCK (self);
  stream = gst_pad_get_element_private (pad);
  if (stream) {
    g_assert (stream->sinkpad == pad);

    gst_stream_synchronizer_release_stream (self, stream);
  }
  GST_STREAM_SYNCHRONIZER_UNLOCK (self);
}

static GstStateChangeReturn
gst_stream_synchronizer_change_state (GstElement * element,
    GstStateChange transition)
{
  GstStreamSynchronizer *self = GST_STREAM_SYNCHRONIZER (element);
  GstStateChangeReturn ret;

  switch (transition) {
    case GST_STATE_CHANGE_NULL_TO_READY:
      GST_DEBUG_OBJECT (self, "State change NULL->READY");
      self->shutdown = FALSE;
      break;
    case GST_STATE_CHANGE_READY_TO_PAUSED:
      GST_DEBUG_OBJECT (self, "State change READY->PAUSED");
      self->group_start_time = 0;
      self->shutdown = FALSE;
      break;
    case GST_STATE_CHANGE_PAUSED_TO_READY:{
      GList *l;

      GST_DEBUG_OBJECT (self, "State change READY->NULL");

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      for (l = self->streams; l; l = l->next) {
        GstStream *ostream = l->data;
        g_cond_broadcast (&ostream->stream_finish_cond);
      }
      self->shutdown = TRUE;
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
    }
    default:
      break;
  }

  ret = GST_ELEMENT_CLASS (parent_class)->change_state (element, transition);
  GST_DEBUG_OBJECT (self, "Base class state changed returned: %d", ret);
  if (G_UNLIKELY (ret != GST_STATE_CHANGE_SUCCESS))
    return ret;

  switch (transition) {
    case GST_STATE_CHANGE_PAUSED_TO_READY:{
      GList *l;

      GST_DEBUG_OBJECT (self, "State change PAUSED->READY");
      self->group_start_time = 0;

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      for (l = self->streams; l; l = l->next) {
        GstStream *stream = l->data;

        gst_segment_init (&stream->segment, GST_FORMAT_UNDEFINED);
        stream->wait = FALSE;
        stream->new_stream = FALSE;
        stream->drop_discont = FALSE;
        stream->is_eos = FALSE;
      }
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
      break;
    }
    case GST_STATE_CHANGE_READY_TO_NULL:{
      GST_DEBUG_OBJECT (self, "State change READY->NULL");

      GST_STREAM_SYNCHRONIZER_LOCK (self);
      self->current_stream_number = 0;
      GST_STREAM_SYNCHRONIZER_UNLOCK (self);
      break;
    }
    default:
      break;
  }

  return ret;
}

/* GObject vfuncs */
static void
gst_stream_synchronizer_finalize (GObject * object)
{
  GstStreamSynchronizer *self = GST_STREAM_SYNCHRONIZER (object);

  g_mutex_clear (&self->lock);

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

/* GObject type initialization */
static void
gst_stream_synchronizer_init (GstStreamSynchronizer * self)
{
  g_mutex_init (&self->lock);
}

static void
gst_stream_synchronizer_class_init (GstStreamSynchronizerClass * klass)
{
  GObjectClass *gobject_class = (GObjectClass *) klass;
  GstElementClass *element_class = (GstElementClass *) klass;

  gobject_class->finalize = gst_stream_synchronizer_finalize;

  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&srctemplate));
  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&sinktemplate));

  gst_element_class_set_static_metadata (element_class,
      "Stream Synchronizer", "Generic",
      "Synchronizes a group of streams to have equal durations and starting points",
      "Sebastian Dröge <sebastian.droege@collabora.co.uk>");

  element_class->change_state =
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_change_state);
  element_class->request_new_pad =
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_request_new_pad);
  element_class->release_pad =
      GST_DEBUG_FUNCPTR (gst_stream_synchronizer_release_pad);
}

gboolean
gst_stream_synchronizer_plugin_init (GstPlugin * plugin)
{
  GST_DEBUG_CATEGORY_INIT (stream_synchronizer_debug,
      "streamsynchronizer", 0, "Stream Synchronizer");

  return gst_element_register (plugin, "streamsynchronizer", GST_RANK_NONE,
      GST_TYPE_STREAM_SYNCHRONIZER);
}