path: root/gst/apetag/gsttagdemux.c

/* GStreamer Base Class for Tag Demuxing
 * Copyright (C) 2005 Jan Schmidt <thaytan@mad.scientist.com>
 * Copyright (C) 2006 Tim-Philipp Müller <tim centricular net>
 *
 * 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:gsttagdemux
 * @see_also: GstApeDemux
 * @short_description: Base class for demuxing tags that are in chunks
 *                     directly at the beginning or at the end of a file
 * 
 * <refsect2>
 * <para>
 * Provides a base class for demuxing tags at the beginning or end of a
 * stream and handles things like typefinding, querying, seeking, and
 * different modes of operation (chain-based, pull_range-based, and providing
 * downstream elements with random access if upstream supports that). The tag
 * is stripped from the output, and all offsets are adjusted for the tag
 * sizes, so that to the downstream element the stream will appear as if
 * there was no tag at all. Also, once the tag has been parsed, GstTagDemux
 * will try to determine the media type of the resulting stream and add a
 * source pad with the appropriate caps in order to facilitate auto-plugging.
 * </para>
 * <title>Deriving from GstTagDemux</title>
 * <para>
 * Subclasses have to do four things:
 * <itemizedlist>
 *  <listitem><para>
 *  In their base init function, they must add a pad template for the sink
 *  pad to the element class, describing the media type they can parse in
 *  the caps of the pad template.
 *  </para></listitem>
 *  <listitem><para>
 *  In their class init function, they must override
 *  GST_TAG_DEMUX_CLASS(demux_klass)->identify_tag with their own identify
 *  function.
 *  </para></listitem>
 *  <listitem><para>
 *  In their class init function, they must override
 *  GST_TAG_DEMUX_CLASS(demux_klass)->parse_tag with their own parse
 *  function.
 *  </para></listitem>
 *  <listitem><para>
 *  In their instance init function, they must set
 *  GST_TAG_DEMUX(demux)->min_start_size and/or 
 *  GST_TAG_DEMUX(demux)->min_end_size to the minimum size required for the
 *  identify function to decide whether the stream has a supported tag or
 *  not. A class parsing ID3v1 tags, for example, would set min_end_size to
 *  128 bytes.
 *  </para></listitem>
 * </itemizedlist>
 * </para>
 * </refsect2>
 */

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

#include "gsttagdemux.h"

#include <gst/gst-i18n-plugin.h>
#include <string.h>

typedef enum
{
  GST_TAG_DEMUX_READ_START_TAG,
  GST_TAG_DEMUX_TYPEFINDING,
  GST_TAG_DEMUX_STREAMING
} GstTagDemuxState;

struct _GstTagDemuxPrivate
{
  GstPad *srcpad;
  GstPad *sinkpad;

  /* Number of bytes to remove from the
   * start of file (tag at beginning) */
  guint strip_start;

  /* Number of bytes to remove from the
   * end of file (tag at end) */
  guint strip_end;

  gint64 upstream_size;

  GstTagDemuxState state;
  GstBuffer *collect;
  GstCaps *src_caps;

  GstTagList *event_tags;
  GstTagList *parsed_tags;
  gboolean send_tag_event;
};

/* Require at least 8kB of data before we attempt typefind. 
 * Seems a decent value based on test files
 * 40kB is massive overkill for the maximum, I think, but it 
 * doesn't do any harm (tpm: increased to 64kB after watching
 * typefinding fail on a wavpack file that needed 42kB to succeed) */
#define TYPE_FIND_MIN_SIZE 8192
#define TYPE_FIND_MAX_SIZE 65536

GST_DEBUG_CATEGORY_STATIC (tagdemux_debug);
#define GST_CAT_DEFAULT (tagdemux_debug)

static GstStaticPadTemplate src_factory = GST_STATIC_PAD_TEMPLATE ("src",
    GST_PAD_SRC,
    GST_PAD_SOMETIMES,
    GST_STATIC_CAPS ("ANY")
    );

static void gst_tag_demux_dispose (GObject * object);

static GstFlowReturn gst_tag_demux_chain (GstPad * pad, GstBuffer * buf);

static gboolean gst_tag_demux_src_activate_pull (GstPad * pad, gboolean active);
static GstFlowReturn gst_tag_demux_read_range (GstTagDemux * tagdemux,
    guint64 offset, guint length, GstBuffer ** buffer);

static gboolean gst_tag_demux_src_checkgetrange (GstPad * srcpad);
static GstFlowReturn gst_tag_demux_src_getrange (GstPad * srcpad,
    guint64 offset, guint length, GstBuffer ** buffer);

static gboolean gst_tag_demux_add_srcpad (GstTagDemux * tagdemux,
    GstCaps * new_caps);
static gboolean gst_tag_demux_remove_srcpad (GstTagDemux * tagdemux);

static gboolean gst_tag_demux_srcpad_event (GstPad * pad, GstEvent * event);
static gboolean gst_tag_demux_sink_activate (GstPad * sinkpad);
static GstStateChangeReturn gst_tag_demux_change_state (GstElement * element,
    GstStateChange transition);
static gboolean gst_tag_demux_pad_query (GstPad * pad, GstQuery * query);
static const GstQueryType *gst_tag_demux_get_query_types (GstPad * pad);
static gboolean gst_tag_demux_get_upstream_size (GstTagDemux * tagdemux);
static GstCaps *gst_tag_demux_do_typefind (GstTagDemux * tagdemux,
    GstBuffer * buffer);
static void gst_tag_demux_send_tag_event (GstTagDemux * tagdemux);

static void gst_tag_demux_base_init (gpointer g_class);
static void gst_tag_demux_class_init (gpointer g_class, gpointer d);
static void gst_tag_demux_init (GstTagDemux * obj, GstTagDemuxClass * klass);

static gpointer parent_class;   /* NULL */

/* Cannot use boilerplate macros here because we want the abstract flag */
GType
gst_tag_demux_get_type (void)
{
  static GType object_type;     /* 0 */

  if (object_type == 0) {
    static const GTypeInfo object_info = {
      sizeof (GstTagDemuxClass),
      gst_tag_demux_base_init,
      NULL,                     /* base_finalize */
      gst_tag_demux_class_init,
      NULL,                     /* class_finalize */
      NULL,                     /* class_data */
      sizeof (GstTagDemux),
      0,                        /* n_preallocs */
      (GInstanceInitFunc) gst_tag_demux_init
    };

    /* FIXME: register as 'GstApeDemuxBase' for now */
    object_type = g_type_register_static (GST_TYPE_ELEMENT,
        "GstTagDemux", &object_info, G_TYPE_FLAG_ABSTRACT);
  }

  return object_type;
}

static void
gst_tag_demux_base_init (gpointer klass)
{
  GstElementClass *element_class = GST_ELEMENT_CLASS (klass);

  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&src_factory));

  GST_DEBUG_CATEGORY_INIT (tagdemux_debug, "tagdemux", 0,
      "GStreamer tag demux base class");
}

static void
gst_tag_demux_class_init (gpointer klass, gpointer d)
{
  GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

  parent_class = g_type_class_peek_parent (klass);

  gobject_class->dispose = gst_tag_demux_dispose;

  element_class->change_state = GST_DEBUG_FUNCPTR (gst_tag_demux_change_state);

  g_type_class_add_private (klass, sizeof (GstTagDemuxPrivate));
}

static void
gst_tag_demux_reset (GstTagDemux * tagdemux)
{
  tagdemux->priv->strip_start = 0;
  tagdemux->priv->strip_end = 0;
  tagdemux->priv->upstream_size = -1;
  tagdemux->priv->state = GST_TAG_DEMUX_READ_START_TAG;
  tagdemux->priv->send_tag_event = FALSE;

  gst_buffer_replace (&(tagdemux->priv->collect), NULL);
  gst_caps_replace (&(tagdemux->priv->src_caps), NULL);

  gst_tag_demux_remove_srcpad (tagdemux);

  if (tagdemux->priv->event_tags) {
    gst_tag_list_free (tagdemux->priv->event_tags);
    tagdemux->priv->event_tags = NULL;
  }
  if (tagdemux->priv->parsed_tags) {
    gst_tag_list_free (tagdemux->priv->parsed_tags);
    tagdemux->priv->parsed_tags = NULL;
  }
}

static void
gst_tag_demux_init (GstTagDemux * demux, GstTagDemuxClass * gclass)
{
  GstElementClass *element_klass = GST_ELEMENT_CLASS (gclass);
  GstPadTemplate *tmpl;

  demux->priv = g_type_instance_get_private ((GTypeInstance *) demux,
      GST_TYPE_TAG_DEMUX);

  /* subclasses must set these to sane values */
  demux->min_start_size = 0;
  demux->min_end_size = 0;

  /* subclasses may set these, we just set defaults */
  demux->prefer_start_tag = TRUE;

  tmpl = gst_element_class_get_pad_template (element_klass, "sink");
  if (tmpl) {
    demux->priv->sinkpad = gst_pad_new_from_template (tmpl, "sink");

    gst_pad_set_activate_function (demux->priv->sinkpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_sink_activate));
    gst_pad_set_chain_function (demux->priv->sinkpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_chain));
    gst_element_add_pad (GST_ELEMENT (demux), demux->priv->sinkpad);
  }

  gst_tag_demux_reset (demux);
}

static void
gst_tag_demux_dispose (GObject * object)
{
  GstTagDemux *tagdemux = GST_TAG_DEMUX (object);

  gst_tag_demux_reset (tagdemux);

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

static gboolean
gst_tag_demux_add_srcpad (GstTagDemux * tagdemux, GstCaps * new_caps)
{
  GstPad *srcpad = NULL;

  if (tagdemux->priv->src_caps == NULL ||
      !gst_caps_is_equal (new_caps, tagdemux->priv->src_caps)) {

    gst_caps_replace (&(tagdemux->priv->src_caps), new_caps);
    if (tagdemux->priv->srcpad != NULL) {
      GST_DEBUG_OBJECT (tagdemux, "Changing src pad caps to %" GST_PTR_FORMAT,
          tagdemux->priv->src_caps);

      gst_pad_set_caps (tagdemux->priv->srcpad, tagdemux->priv->src_caps);
    }
  } else {
    /* Caps never changed */
    gst_caps_unref (new_caps);
  }

  if (tagdemux->priv->srcpad == NULL) {
    srcpad = tagdemux->priv->srcpad =
        gst_pad_new_from_template (gst_element_class_get_pad_template
        (GST_ELEMENT_GET_CLASS (tagdemux), "src"), "src");
    g_return_val_if_fail (tagdemux->priv->srcpad != NULL, FALSE);

    gst_pad_set_query_type_function (tagdemux->priv->srcpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_get_query_types));
    gst_pad_set_query_function (tagdemux->priv->srcpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_pad_query));
    gst_pad_set_event_function (tagdemux->priv->srcpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_srcpad_event));
    gst_pad_set_activatepull_function (tagdemux->priv->srcpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_src_activate_pull));
    gst_pad_set_checkgetrange_function (tagdemux->priv->srcpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_src_checkgetrange));
    gst_pad_set_getrange_function (tagdemux->priv->srcpad,
        GST_DEBUG_FUNCPTR (gst_tag_demux_src_getrange));

    gst_pad_use_fixed_caps (tagdemux->priv->srcpad);

    if (tagdemux->priv->src_caps)
      gst_pad_set_caps (tagdemux->priv->srcpad, tagdemux->priv->src_caps);

    GST_DEBUG_OBJECT (tagdemux, "Adding src pad with caps %" GST_PTR_FORMAT,
        tagdemux->priv->src_caps);

    gst_object_ref (tagdemux->priv->srcpad);
    if (!(gst_element_add_pad (GST_ELEMENT (tagdemux), tagdemux->priv->srcpad)))
      return FALSE;
    gst_element_no_more_pads (GST_ELEMENT (tagdemux));
  }

  return TRUE;
}

static gboolean
gst_tag_demux_remove_srcpad (GstTagDemux * demux)
{
  gboolean res = TRUE;

  if (demux->priv->srcpad != NULL) {
    GST_DEBUG_OBJECT (demux, "Removing src pad");
    res = gst_element_remove_pad (GST_ELEMENT (demux), demux->priv->srcpad);
    g_return_val_if_fail (res != FALSE, FALSE);
    gst_object_unref (demux->priv->srcpad);
    demux->priv->srcpad = NULL;
  }

  return res;
};

static gboolean
gst_tag_demux_trim_buffer (GstTagDemux * tagdemux, GstBuffer ** buf_ref)
{
  GstBuffer *buf = *buf_ref;

  guint trim_start = 0;
  guint out_size = GST_BUFFER_SIZE (buf);
  guint64 out_offset = GST_BUFFER_OFFSET (buf);
  gboolean need_sub = FALSE;

  /* Adjust offset and length */
  if (!GST_BUFFER_OFFSET_IS_VALID (buf)) {
    /* Can't change anything without an offset */
    return TRUE;
  }

  /* If the buffer crosses the tag at the end of file, trim it */
  if (tagdemux->priv->strip_end > 0) {
    if (gst_tag_demux_get_upstream_size (tagdemux)) {
      guint64 v1tag_offset =
          tagdemux->priv->upstream_size - tagdemux->priv->strip_end;

      if (out_offset >= v1tag_offset) {
        GST_DEBUG_OBJECT (tagdemux, "Buffer is past the end of the data");
        goto no_out_buffer;
      }

      if (out_offset + out_size > v1tag_offset) {
        out_size = v1tag_offset - out_offset;
        need_sub = TRUE;
      }
    }
  }

  if (tagdemux->priv->strip_start > 0) {
    /* If the buffer crosses the tag at the start of file, trim it */
    if (out_offset <= tagdemux->priv->strip_start) {
      if (out_offset + out_size <= tagdemux->priv->strip_start) {
        GST_DEBUG_OBJECT (tagdemux, "Buffer is before the start of the data");
        goto no_out_buffer;
      }

      trim_start = tagdemux->priv->strip_start - out_offset;
      out_size -= trim_start;
      out_offset = 0;
    } else {
      out_offset -= tagdemux->priv->strip_start;
    }
    need_sub = TRUE;
  }

  g_assert (out_size > 0);

  if (need_sub == TRUE) {
    if (out_size != GST_BUFFER_SIZE (buf) || !gst_buffer_is_writable (buf)) {
      GstBuffer *sub;

      GST_DEBUG_OBJECT (tagdemux, "Sub-buffering to trim size %d offset %"
          G_GINT64_FORMAT " to %d offset %" G_GINT64_FORMAT,
          GST_BUFFER_SIZE (buf), GST_BUFFER_OFFSET (buf), out_size, out_offset);

      sub = gst_buffer_create_sub (buf, trim_start, out_size);
      g_return_val_if_fail (sub != NULL, FALSE);
      gst_buffer_unref (buf);
      *buf_ref = buf = sub;
    } else {
      GST_DEBUG_OBJECT (tagdemux, "Adjusting buffer from size %d offset %"
          G_GINT64_FORMAT " to %d offset %" G_GINT64_FORMAT,
          GST_BUFFER_SIZE (buf), GST_BUFFER_OFFSET (buf), out_size, out_offset);
    }

    GST_BUFFER_OFFSET (buf) = out_offset;
    GST_BUFFER_OFFSET_END (buf) = out_offset + out_size;
    gst_buffer_set_caps (buf, tagdemux->priv->src_caps);
  }

  return TRUE;

no_out_buffer:
  gst_buffer_unref (buf);
  *buf_ref = NULL;
  return TRUE;
}

static void
gst_tag_demux_chain_parse_tag (GstTagDemux * demux, GstBuffer * collect)
{
  GstTagDemuxResult parse_ret;
  GstTagDemuxClass *klass;
  guint tagsize = 0;
  guint available;

  klass = GST_TAG_DEMUX_CLASS (G_OBJECT_GET_CLASS (demux));

  /* If we receive a buffer that's from the middle of the file, 
   * we can't read tags so move to typefinding */
  if (GST_BUFFER_OFFSET (collect) != 0) {
    GST_DEBUG_OBJECT (demux, "Received buffer from non-zero offset %"
        G_GINT64_FORMAT ". Can't read tags", GST_BUFFER_OFFSET (collect));
    demux->priv->state = GST_TAG_DEMUX_TYPEFINDING;
    return;
  }

  g_assert (klass->identify_tag != NULL);
  g_assert (klass->parse_tag != NULL);

  available = GST_BUFFER_SIZE (collect);

  if (available < demux->min_start_size) {
    GST_DEBUG_OBJECT (demux, "Only %u bytes available, but %u needed "
        "to identify tag", available, demux->min_start_size);
    return;                     /* wait for more data */
  }

  if (!klass->identify_tag (demux, collect, TRUE, &tagsize)) {
    GST_DEBUG_OBJECT (demux, "Could not identify start tag");
    demux->priv->state = GST_TAG_DEMUX_TYPEFINDING;
    return;
  }

  GST_DEBUG_OBJECT (demux, "Identified tag, size = %u bytes", tagsize);

  do {
    GstTagList *tags = NULL;
    guint newsize, saved_size;

    demux->priv->strip_start = tagsize;

    if (available < tagsize) {
      GST_DEBUG_OBJECT (demux, "Only %u bytes available, but %u needed "
          "to parse tag", available, tagsize);
      return;                   /* wait for more data */
    }

    saved_size = GST_BUFFER_SIZE (collect);
    GST_BUFFER_SIZE (collect) = tagsize;
    newsize = tagsize;

    parse_ret = klass->parse_tag (demux, collect, TRUE, &newsize, &tags);

    GST_BUFFER_SIZE (collect) = saved_size;

    switch (parse_ret) {
      case GST_TAG_DEMUX_RESULT_OK:
        demux->priv->strip_start = newsize;
        demux->priv->parsed_tags = tags;
        GST_DEBUG_OBJECT (demux, "Read start tag of size %u", newsize);
        break;
      case GST_TAG_DEMUX_RESULT_BROKEN_TAG:
        demux->priv->strip_start = newsize;
        demux->priv->parsed_tags = tags;
        GST_WARNING_OBJECT (demux, "Ignoring broken start tag of size %d",
            demux->priv->strip_start);
        break;
      case GST_TAG_DEMUX_RESULT_AGAIN:
        GST_DEBUG_OBJECT (demux, "Re-parse, this time with %u bytes", newsize);
        g_assert (newsize != tagsize);
        tagsize = newsize;
        break;
    }
  } while (parse_ret == GST_TAG_DEMUX_RESULT_AGAIN);

  GST_LOG_OBJECT (demux, "Parsed tag. Proceeding to typefinding");
  demux->priv->state = GST_TAG_DEMUX_TYPEFINDING;
  demux->priv->send_tag_event = TRUE;
}

static GstFlowReturn
gst_tag_demux_chain (GstPad * pad, GstBuffer * buf)
{
  GstTagDemux *demux;

  demux = GST_TAG_DEMUX (GST_PAD_PARENT (pad));
  g_return_val_if_fail (GST_IS_TAG_DEMUX (demux), GST_FLOW_ERROR);

  if (demux->priv->collect == NULL) {
    demux->priv->collect = buf;
  } else {
    demux->priv->collect = gst_buffer_join (demux->priv->collect, buf);
  }
  buf = NULL;

  switch (demux->priv->state) {
    case GST_TAG_DEMUX_READ_START_TAG:
      gst_tag_demux_chain_parse_tag (demux, demux->priv->collect);
      if (demux->priv->state != GST_TAG_DEMUX_TYPEFINDING)
        break;
      /* Fall-through */
    case GST_TAG_DEMUX_TYPEFINDING:{
      GstCaps *caps;
      GstBuffer *typefind_buf = NULL;

      if (GST_BUFFER_SIZE (demux->priv->collect) < TYPE_FIND_MIN_SIZE)
        break;                  /* Go get more data first */

      GST_DEBUG_OBJECT (demux, "Typefinding with size %d",
          GST_BUFFER_SIZE (demux->priv->collect));

      /* Trim the buffer and adjust offset for typefinding */
      typefind_buf = demux->priv->collect;
      gst_buffer_ref (typefind_buf);
      if (!gst_tag_demux_trim_buffer (demux, &typefind_buf))
        return GST_FLOW_ERROR;

      caps = gst_tag_demux_do_typefind (demux, typefind_buf);

      if (caps == NULL) {
        if (GST_BUFFER_SIZE (typefind_buf) < TYPE_FIND_MAX_SIZE) {
          /* Just break for more data */
          gst_buffer_unref (typefind_buf);
          return GST_FLOW_OK;
        }

        /* We failed typefind */
        GST_ELEMENT_ERROR (demux, STREAM, TYPE_NOT_FOUND, (NULL), (NULL));
        gst_buffer_unref (typefind_buf);
        gst_buffer_unref (demux->priv->collect);
        demux->priv->collect = NULL;
        return GST_FLOW_ERROR;
      }
      gst_buffer_unref (typefind_buf);

      if (!gst_tag_demux_add_srcpad (demux, caps)) {
        GST_DEBUG_OBJECT (demux, "Failed to add srcpad");
        gst_caps_unref (caps);
        goto error;
      }
      gst_caps_unref (caps);

      /* Move onto streaming and fall-through to push out existing
       * data */
      demux->priv->state = GST_TAG_DEMUX_STREAMING;
      /* fall-through */
    }
    case GST_TAG_DEMUX_STREAMING:{
      GstBuffer *outbuf = NULL;

      if (demux->priv->send_tag_event) {
        gst_tag_demux_send_tag_event (demux);
        demux->priv->send_tag_event = FALSE;
      }

      /* Trim the buffer and adjust offset */
      if (demux->priv->collect) {
        outbuf = demux->priv->collect;
        demux->priv->collect = NULL;
        if (!gst_tag_demux_trim_buffer (demux, &outbuf))
          return GST_FLOW_ERROR;
      }
      if (outbuf) {
        if (G_UNLIKELY (demux->priv->srcpad == NULL)) {
          gst_buffer_unref (outbuf);
          return GST_FLOW_ERROR;
        }

        GST_DEBUG_OBJECT (demux, "Pushing buffer %p", outbuf);
        /* gst_util_dump_mem (GST_BUFFER_DATA (outbuf),
           GST_BUFFER_SIZE (outbuf)); */
        return gst_pad_push (demux->priv->srcpad, outbuf);
      }
    }
  }
  return GST_FLOW_OK;

error:
  GST_DEBUG_OBJECT (demux, "error in chain function");

  return GST_FLOW_ERROR;
}

static gboolean
gst_tag_demux_get_upstream_size (GstTagDemux * tagdemux)
{
  GstPad *peer = NULL;
  GstFormat format;
  gint64 result;
  gboolean res = FALSE;

  /* Short-cut if we already queried upstream */
  if (tagdemux->priv->upstream_size > 0)
    return TRUE;

  if ((peer = gst_pad_get_peer (tagdemux->priv->sinkpad)) == NULL)
    return FALSE;

  format = GST_FORMAT_BYTES;
  if (gst_pad_query_duration (peer, &format, &result) &&
      format == GST_FORMAT_BYTES && result > 0) {
    tagdemux->priv->upstream_size = result;
    res = TRUE;
  }

  gst_object_unref (peer);
  return res;
}

static gboolean
gst_tag_demux_srcpad_event (GstPad * pad, GstEvent * event)
{
  gboolean res = FALSE;
  GstTagDemux *tagdemux = GST_TAG_DEMUX (GST_PAD_PARENT (pad));

  /* Handle SEEK events, with adjusted byte offsets and sizes. */

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_SEEK:
    {
      gdouble rate;
      GstFormat format;
      GstSeekType cur_type, stop_type;
      GstSeekFlags flags;
      gint64 cur, stop;

      gst_event_parse_seek (event, &rate, &format, &flags,
          &cur_type, &cur, &stop_type, &stop);

      if (format == GST_FORMAT_BYTES &&
          tagdemux->priv->state == GST_TAG_DEMUX_STREAMING &&
          gst_pad_is_linked (tagdemux->priv->sinkpad)) {
        GstEvent *upstream;

        switch (cur_type) {
          case GST_SEEK_TYPE_SET:
            cur += tagdemux->priv->strip_start;
            break;
          case GST_SEEK_TYPE_CUR:
            break;
          case GST_SEEK_TYPE_END:
            cur += tagdemux->priv->strip_end;
            break;
          default:
            g_assert_not_reached ();
            break;
        }
        switch (stop_type) {
          case GST_SEEK_TYPE_SET:
            stop += tagdemux->priv->strip_start;
            break;
          case GST_SEEK_TYPE_CUR:
            break;
          case GST_SEEK_TYPE_END:
            stop += tagdemux->priv->strip_end;
            break;
          default:
            break;
        }
        upstream = gst_event_new_seek (rate, format, flags,
            cur_type, cur, stop_type, stop);
        res = gst_pad_push_event (tagdemux->priv->sinkpad, upstream);
      }
      break;
    }
    default:
      break;
  }

  gst_event_unref (event);
  return res;
}

/* takes ownership of new_tags */

static void
gst_tag_demux_merge_tags (GstTagList ** tags, GstTagList * new_tags)
{
  g_return_if_fail (tags != NULL);

  if (new_tags == NULL)
    return;

  GST_LOG ("New tags: %" GST_PTR_FORMAT, new_tags);

  if (*tags != NULL) {
    GstTagList *merged;

    merged = gst_tag_list_merge (*tags, new_tags, GST_TAG_MERGE_REPLACE);
    gst_tag_list_free (*tags);
    gst_tag_list_free (new_tags);
    *tags = merged;
  } else {
    *tags = new_tags;
  }

  GST_LOG ("Tags now: %" GST_PTR_FORMAT, *tags);
}

/* Read and interpret any end tag when activating in pull_range.
 * Returns FALSE if pad activation should fail. */
static gboolean
gst_tag_demux_pull_end_tag (GstTagDemux * demux, GstTagList ** tags)
{
  GstTagDemuxResult parse_ret;
  GstTagDemuxClass *klass;
  GstFlowReturn flow_ret;
  GstTagList *new_tags = NULL;
  GstBuffer *buffer = NULL;
  gboolean have_tag;
  gboolean res = FALSE;
  guint64 offset;
  guint tagsize;

  klass = GST_TAG_DEMUX_CLASS (G_OBJECT_GET_CLASS (demux));

  g_assert (klass->identify_tag != NULL);
  g_assert (klass->parse_tag != NULL);

  if (demux->min_end_size == 0) {
    GST_DEBUG_OBJECT (demux, "Not looking for tag at the end");
    return TRUE;
  }

  if (demux->priv->upstream_size < demux->min_end_size) {
    GST_DEBUG_OBJECT (demux, "File too small");
    return TRUE;
  }

  /* Pull enough to identify the tag and retrieve its total size */
  offset = demux->priv->upstream_size - demux->min_end_size;

  flow_ret = gst_pad_pull_range (demux->priv->sinkpad, offset,
      demux->min_end_size, &buffer);

  if (flow_ret != GST_FLOW_OK) {
    GST_DEBUG_OBJECT (demux, "Could not read tag header from end of file, "
        "ret = %s", gst_flow_get_name (flow_ret));
    goto done;
  }

  if (GST_BUFFER_SIZE (buffer) < demux->min_end_size) {
    GST_DEBUG_OBJECT (demux, "Only managed to read %u bytes from file "
        "(required: %u bytes)", GST_BUFFER_SIZE (buffer), demux->min_end_size);
    goto done;
  }

  have_tag = klass->identify_tag (demux, buffer, FALSE, &tagsize);

  if (!have_tag) {
    GST_DEBUG_OBJECT (demux, "Could not find tag at end");
    goto done;
  }

  /* Now pull the entire tag */
  do {
    guint newsize, saved_size;

    GST_DEBUG_OBJECT (demux, "Identified tag at end, size=%u bytes", tagsize);

    demux->priv->strip_end = tagsize;

    g_assert (tagsize >= demux->min_end_size);

    /* Get buffer that's exactly the requested size */
    if (GST_BUFFER_SIZE (buffer) != tagsize) {
      gst_buffer_unref (buffer);
      buffer = NULL;

      offset = demux->priv->upstream_size - tagsize;

      flow_ret = gst_pad_pull_range (demux->priv->sinkpad, offset,
          tagsize, &buffer);

      if (flow_ret != GST_FLOW_OK) {
        GST_DEBUG_OBJECT (demux, "Could not read data from end of file at "
            "offset %" G_GUINT64_FORMAT ". ret = %s", offset,
            gst_flow_get_name (flow_ret));
        goto done;
      }

      if (GST_BUFFER_SIZE (buffer) < tagsize) {
        GST_DEBUG_OBJECT (demux, "Only managed to read %u bytes from file",
            GST_BUFFER_SIZE (buffer));
        goto done;
      }
    }

    GST_BUFFER_OFFSET (buffer) = offset;

    saved_size = GST_BUFFER_SIZE (buffer);
    GST_BUFFER_SIZE (buffer) = tagsize;
    newsize = tagsize;

    parse_ret = klass->parse_tag (demux, buffer, FALSE, &newsize, &new_tags);

    GST_BUFFER_SIZE (buffer) = saved_size;

    switch (parse_ret) {
      case GST_TAG_DEMUX_RESULT_OK:
        res = TRUE;
        demux->priv->strip_end = newsize;
        GST_DEBUG_OBJECT (demux, "Read tag at end, size %d",
            demux->priv->strip_end);
        break;
      case GST_TAG_DEMUX_RESULT_BROKEN_TAG:
        res = TRUE;
        demux->priv->strip_end = newsize;
        GST_WARNING_OBJECT (demux, "Ignoring broken tag at end, size %d",
            demux->priv->strip_end);
        break;
      case GST_TAG_DEMUX_RESULT_AGAIN:
        GST_DEBUG_OBJECT (demux, "Re-parse, this time with %d bytes", newsize);
        g_assert (newsize != tagsize);
        tagsize = newsize;
        break;
    }
  } while (parse_ret == GST_TAG_DEMUX_RESULT_AGAIN);

  gst_tag_demux_merge_tags (tags, new_tags);
  new_tags = NULL;

done:
  if (new_tags)
    gst_tag_list_free (new_tags);
  if (buffer)
    gst_buffer_unref (buffer);
  return res;
}

/* Read and interpret any tag at the start when activating in
 * pull_range. Returns FALSE if pad activation should fail. */
static gboolean
gst_tag_demux_pull_start_tag (GstTagDemux * demux, GstTagList ** tags)
{
  GstTagDemuxResult parse_ret;
  GstTagDemuxClass *klass;
  GstFlowReturn flow_ret;
  GstTagList *new_tags = NULL;
  GstBuffer *buffer = NULL;
  gboolean have_tag;
  gboolean res = FALSE;
  guint req, tagsize;

  klass = GST_TAG_DEMUX_CLASS (G_OBJECT_GET_CLASS (demux));

  g_assert (klass->identify_tag != NULL);
  g_assert (klass->parse_tag != NULL);

  if (demux->min_start_size == 0) {
    GST_DEBUG_OBJECT (demux, "Not looking for tag at the beginning");
    return TRUE;
  }

  /* Handle tag at start. Try with 4kB to start with */
  req = MAX (demux->min_start_size, 4096);

  /* Pull enough to identify the tag and retrieve its total size */
  flow_ret = gst_pad_pull_range (demux->priv->sinkpad, 0, req, &buffer);
  if (flow_ret != GST_FLOW_OK) {
    GST_DEBUG_OBJECT (demux, "Could not read data from start of file ret=%s",
        gst_flow_get_name (flow_ret));
    goto done;
  }

  if (GST_BUFFER_SIZE (buffer) < demux->min_start_size) {
    GST_DEBUG_OBJECT (demux, "Only managed to read %u bytes from file - "
        "no tag in this file", GST_BUFFER_SIZE (buffer));
    goto done;
  }

  have_tag = klass->identify_tag (demux, buffer, TRUE, &tagsize);

  if (!have_tag) {
    GST_DEBUG_OBJECT (demux, "Could not find start tag");
    res = TRUE;
    goto done;
  }

  GST_DEBUG_OBJECT (demux, "Identified start tag, size = %u bytes", tagsize);

  do {
    guint newsize, saved_size;

    demux->priv->strip_start = tagsize;

    /* Now pull the entire tag */
    g_assert (tagsize >= demux->min_start_size);

    if (GST_BUFFER_SIZE (buffer) < tagsize) {
      gst_buffer_unref (buffer);
      buffer = NULL;

      flow_ret = gst_pad_pull_range (demux->priv->sinkpad, 0, tagsize, &buffer);
      if (flow_ret != GST_FLOW_OK) {
        GST_DEBUG_OBJECT (demux, "Could not read data from start of file, "
            "ret = %s", gst_flow_get_name (flow_ret));
        goto done;
      }

      if (GST_BUFFER_SIZE (buffer) < tagsize) {
        GST_DEBUG_OBJECT (demux, "Only managed to read %u bytes from file",
            GST_BUFFER_SIZE (buffer));
        goto done;
      }
    }

    saved_size = GST_BUFFER_SIZE (buffer);
    GST_BUFFER_SIZE (buffer) = tagsize;
    newsize = tagsize;
    parse_ret = klass->parse_tag (demux, buffer, TRUE, &newsize, &new_tags);

    GST_BUFFER_SIZE (buffer) = saved_size;

    switch (parse_ret) {
      case GST_TAG_DEMUX_RESULT_OK:
        res = TRUE;
        demux->priv->strip_start = newsize;
        GST_DEBUG_OBJECT (demux, "Read start tag of size %d", newsize);
        break;
      case GST_TAG_DEMUX_RESULT_BROKEN_TAG:
        res = TRUE;
        demux->priv->strip_start = newsize;
        GST_WARNING_OBJECT (demux, "Ignoring broken start tag of size %d",
            demux->priv->strip_start);
        break;
      case GST_TAG_DEMUX_RESULT_AGAIN:
        GST_DEBUG_OBJECT (demux, "Re-parse, this time with %d bytes", newsize);
        g_assert (newsize != tagsize);
        tagsize = newsize;
        break;
    }
  } while (parse_ret == GST_TAG_DEMUX_RESULT_AGAIN);

  gst_tag_demux_merge_tags (tags, new_tags);
  new_tags = NULL;

done:
  if (new_tags)
    gst_tag_list_free (new_tags);
  if (buffer)
    gst_buffer_unref (buffer);
  return res;
}

/* This function operates similarly to gst_type_find_element_activate
 * in the typefind element
 * 1. try to activate in pull mode. if not, switch to push and succeed.
 * 2. try to read tags in pull mode
 * 3. typefind the contents
 * 4. deactivate pull mode.
 * 5. if we didn't find any caps, fail.
 * 6. Add the srcpad
 * 7. if the sink pad is activated, we are in pull mode. succeed.
 *    otherwise activate both pads in push mode and succeed.
 */
static gboolean
gst_tag_demux_sink_activate (GstPad * sinkpad)
{
  GstTagDemux *demux = GST_TAG_DEMUX (GST_PAD_PARENT (sinkpad));
  gboolean ret = FALSE;
  GstBuffer *buf = NULL;
  GstCaps *caps = NULL;
  GstFlowReturn flow_ret;

  /* 1: */
  /* If we can activate pull_range upstream, then read any end and start
   * tags, otherwise activate in push mode and the chain function will 
   * collect buffers, read the start tag and output a buffer to end
   * preroll.
   */
  if (!gst_pad_check_pull_range (sinkpad) ||
      !gst_pad_activate_pull (sinkpad, TRUE)) {
    GST_DEBUG_OBJECT (demux, "No pull mode. Changing to push, but won't be "
        "able to read end tags");
    demux->priv->state = GST_TAG_DEMUX_READ_START_TAG;
    return gst_pad_activate_push (sinkpad, TRUE);
  }

  /* Look for tags at start and end of file */
  GST_DEBUG_OBJECT (demux, "Activated pull mode. Looking for tags");
  if (!gst_tag_demux_get_upstream_size (demux))
    return FALSE;

  demux->priv->strip_start = 0;
  demux->priv->strip_end = 0;

  /* we merge in REPLACE mode, so read the less important tag first */
  if (demux->prefer_start_tag) {
    if (!gst_tag_demux_pull_end_tag (demux, &demux->priv->parsed_tags) &&
        !gst_tag_demux_pull_start_tag (demux, &demux->priv->parsed_tags)) {
      return FALSE;
    }
  } else {
    if (!gst_tag_demux_pull_start_tag (demux, &demux->priv->parsed_tags) &&
        !gst_tag_demux_pull_end_tag (demux, &demux->priv->parsed_tags)) {
      return FALSE;
    }
  }

  if (demux->priv->parsed_tags != NULL) {
    demux->priv->send_tag_event = TRUE;
  }

  flow_ret = gst_tag_demux_read_range (demux, 0, TYPE_FIND_MAX_SIZE, &buf);
  if (flow_ret != GST_FLOW_OK) {
    GST_DEBUG_OBJECT (demux, "Could not read data from start of file ret=%s",
        gst_flow_get_name (flow_ret));
    goto done_activate;
  }

  /* gst_util_dump_mem (GST_BUFFER_DATA (buf), GST_BUFFER_SIZE (buf)); */
  caps = gst_tag_demux_do_typefind (demux, buf);
  gst_buffer_unref (buf);
  buf = NULL;

  /* 4 - Deactivate pull mode */
  if (!gst_pad_activate_pull (sinkpad, FALSE)) {
    if (caps)
      gst_caps_unref (caps);
    GST_DEBUG_OBJECT (demux, "Could not deactivate sinkpad after reading tags");
    return FALSE;
  }

  /* 5 - If we didn't find the caps, fail */
  if (caps == NULL) {
    GST_DEBUG_OBJECT (demux, "Could not detect type of contents");
    GST_ELEMENT_ERROR (demux, STREAM, TYPE_NOT_FOUND, (NULL), (NULL));
    goto done_activate;
  }

  /* tag reading and typefinding were already done, don't do them again in
   * the chain function if we end up in push mode */
  demux->priv->state = GST_TAG_DEMUX_STREAMING;

  /* 6 Add the srcpad for output now we know caps. */
  /* add_srcpad takes ownership of the caps */
  if (!gst_tag_demux_add_srcpad (demux, caps)) {
    GST_DEBUG_OBJECT (demux, "Could not add source pad");
    goto done_activate;
  }

  /* 7 - if the sinkpad is active, it was done by downstream so we're 
   * done, otherwise switch to push */
  ret = TRUE;
  if (!gst_pad_is_active (sinkpad)) {
    ret = gst_pad_activate_push (demux->priv->srcpad, TRUE);
    ret &= gst_pad_activate_push (sinkpad, TRUE);
  }

done_activate:
  if (buf)
    gst_buffer_unref (buf);

  return ret;
}

static gboolean
gst_tag_demux_src_activate_pull (GstPad * pad, gboolean active)
{
  GstTagDemux *demux = GST_TAG_DEMUX (GST_PAD_PARENT (pad));

  return gst_pad_activate_pull (demux->priv->sinkpad, active);
}

static gboolean
gst_tag_demux_src_checkgetrange (GstPad * srcpad)
{
  GstTagDemux *demux = GST_TAG_DEMUX (GST_PAD_PARENT (srcpad));

  return gst_pad_check_pull_range (demux->priv->sinkpad);
}

static GstFlowReturn
gst_tag_demux_read_range (GstTagDemux * demux,
    guint64 offset, guint length, GstBuffer ** buffer)
{
  GstFlowReturn ret;
  guint64 in_offset;
  guint in_length;

  g_return_val_if_fail (buffer != NULL, GST_FLOW_ERROR);

  /* Adjust offset and length of the request to trim off tag information. 
   * For the returned buffer, adjust the output offset to match what downstream
   * should see */
  in_offset = offset + demux->priv->strip_start;

  if (!gst_tag_demux_get_upstream_size (demux))
    return GST_FLOW_ERROR;

  if (in_offset + length >= demux->priv->upstream_size - demux->priv->strip_end)
    in_length = demux->priv->upstream_size - demux->priv->strip_end - in_offset;
  else
    in_length = length;

  ret = gst_pad_pull_range (demux->priv->sinkpad, in_offset, in_length, buffer);

  if (ret == GST_FLOW_OK && *buffer) {
    if (!gst_tag_demux_trim_buffer (demux, buffer))
      goto error;
  }

  return ret;

error:
  if (*buffer != NULL) {
    gst_buffer_unref (buffer);
    *buffer = NULL;
  }
  return GST_FLOW_ERROR;
}

static GstFlowReturn
gst_tag_demux_src_getrange (GstPad * srcpad,
    guint64 offset, guint length, GstBuffer ** buffer)
{
  GstTagDemux *demux = GST_TAG_DEMUX (GST_PAD_PARENT (srcpad));
  GstFlowReturn flow_ret;

  if (demux->priv->send_tag_event) {
    gst_tag_demux_send_tag_event (demux);
    demux->priv->send_tag_event = FALSE;
  }
  flow_ret = gst_tag_demux_read_range (demux, offset, length, buffer);
/*
  if (flow_ret == GST_FLOW_OK) {
    gst_util_dump_mem (GST_BUFFER_DATA (*buffer), GST_BUFFER_SIZE (*buffer));
  }
*/
  return flow_ret;
}

static GstStateChangeReturn
gst_tag_demux_change_state (GstElement * element, GstStateChange transition)
{
  GstStateChangeReturn ret;
  GstTagDemux *demux = GST_TAG_DEMUX (element);

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

  switch (transition) {
    case GST_STATE_CHANGE_PAUSED_TO_READY:
      gst_tag_demux_reset (demux);
      break;
    default:
      break;
  }
  return ret;
}

static gboolean
gst_tag_demux_pad_query (GstPad * pad, GstQuery * query)
{
  /* For a position or duration query, adjust the returned
   * bytes to strip off the end and start areas */

  GstTagDemux *demux = GST_TAG_DEMUX (GST_PAD_PARENT (pad));
  GstPad *peer = NULL;
  GstFormat format;
  gint64 result;

  if ((peer = gst_pad_get_peer (demux->priv->sinkpad)) == NULL)
    return FALSE;

  if (!gst_pad_query (peer, query)) {
    gst_object_unref (peer);
    return FALSE;
  }

  gst_object_unref (peer);

  switch (GST_QUERY_TYPE (query)) {
    case GST_QUERY_POSITION:
    {
      gst_query_parse_position (query, &format, &result);
      if (format == GST_FORMAT_BYTES) {
        result -= demux->priv->strip_start;
        gst_query_set_position (query, format, result);
      }
      break;
    }
    case GST_QUERY_DURATION:
    {
      gst_query_parse_duration (query, &format, &result);
      if (format == GST_FORMAT_BYTES) {
        result -= demux->priv->strip_start + demux->priv->strip_end;
        gst_query_set_duration (query, format, result);
      }
      break;
    }
    default:
      break;
  }

  return TRUE;
}

static const GstQueryType *
gst_tag_demux_get_query_types (GstPad * pad)
{
  static const GstQueryType types[] = {
    GST_QUERY_POSITION,
    GST_QUERY_DURATION,
    0
  };

  return types;
}

typedef struct
{
  guint best_probability;
  GstCaps *caps;
  GstBuffer *buffer;
} SimpleTypeFind;

static guint8 *
simple_find_peek (gpointer data, gint64 offset, guint size)
{
  SimpleTypeFind *find = (SimpleTypeFind *) data;

  if (offset < 0)
    return NULL;

  if (GST_BUFFER_SIZE (find->buffer) >= offset + size) {
    return GST_BUFFER_DATA (find->buffer) + offset;
  }
  return NULL;
}
static void
simple_find_suggest (gpointer data, guint probability, const GstCaps * caps)
{
  SimpleTypeFind *find = (SimpleTypeFind *) data;

  if (probability > find->best_probability) {
    GstCaps *copy = gst_caps_copy (caps);

    gst_caps_replace (&find->caps, copy);
    gst_caps_unref (copy);
    find->best_probability = probability;
  }
}

static GstCaps *
gst_tag_demux_do_typefind (GstTagDemux * tagdemux, GstBuffer * buffer)
{
  GList *walk, *type_list;
  SimpleTypeFind find;
  GstTypeFind gst_find;

  walk = type_list = gst_type_find_factory_get_list ();

  find.buffer = buffer;
  find.best_probability = 0;
  find.caps = NULL;
  gst_find.data = &find;
  gst_find.peek = simple_find_peek;
  gst_find.get_length = NULL;
  gst_find.suggest = simple_find_suggest;
  while (walk) {
    GstTypeFindFactory *factory = GST_TYPE_FIND_FACTORY (walk->data);

    gst_type_find_factory_call_function (factory, &gst_find);
    if (find.best_probability >= GST_TYPE_FIND_MAXIMUM)
      break;
    walk = g_list_next (walk);
  }
  gst_plugin_feature_list_free (type_list);
  if (find.best_probability > 0) {
    GST_DEBUG ("Found caps %" GST_PTR_FORMAT " with buf size %u", find.caps,
        GST_BUFFER_SIZE (buffer));
    return find.caps;
  }

  gst_caps_replace (&find.caps, NULL);
  return NULL;
}

static void
gst_tag_demux_send_tag_event (GstTagDemux * demux)
{
  /* FIXME: what's the correct merge mode? Docs need to tell... */
  GstTagList *merged = gst_tag_list_merge (demux->priv->event_tags,
      demux->priv->parsed_tags, GST_TAG_MERGE_KEEP);

  if (demux->priv->parsed_tags)
    gst_element_post_message (GST_ELEMENT (demux),
        gst_message_new_tag (GST_OBJECT (demux),
            gst_tag_list_copy (demux->priv->parsed_tags)));

  if (merged) {
    GstEvent *event = gst_event_new_tag (merged);

    GST_EVENT_TIMESTAMP (event) = 0;
    GST_DEBUG_OBJECT (demux, "Sending tag event on src pad");
    gst_pad_push_event (demux->priv->srcpad, event);
  }
}