gstreamer/gst/id3demux/gstid3demux.c

/* -*- Mode: C; tab-width: 2; indent-tabs-mode: t; c-basic-offset: 2 -*- */
/* Copyright 2005 Jan Schmidt <thaytan@mad.scientist.com>
 * Copyright (C) 2003-2004 Benjamin Otte <otte@gnome.org>
 *
 * 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:element-id3demux
 * @short_description: reads tag information from ID3v1 and ID3v2 (<= 2.4.0) data blocks and outputs them as GStreamer tag messages and events.
 *
 * <refsect2>
 * <para>
 * id3demux accepts data streams with either (or both) ID3v2 regions at the start, or ID3v1 at the end. The mime type of the data between the tag blocks is detected using typefind functions, and the appropriate output mime type set on outgoing buffers. 
 * </para><para>
 * The element is only able to read ID3v1 tags from a seekable stream, because they are at the end of the stream. That is, when get_range mode is supported by the upstream elements. If get_range operation is available, id3demux makes it available downstream. This means that elements which require get_range mode, such as wavparse, can operate on files containing ID3 tag information.
 * </para>
 * <title>Example launch line</title>
 * <para>
 * <programlisting>
 * gst-launch filesrc location=file.mp3 ! id3demux ! fakesink -t
 * </programlisting>
 * This pipeline should read any available ID3 tag information and output it. The contents of the file inside the ID3 tag regions should be detected, and the appropriate mime type set on buffers produced from id3demux.
 * </para><para>
 * This id3demux element replaced an older element with the same name which relied on libid3tag from the MAD project.
 * </para>
 * </refsect2>
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <gst/gst.h>
#include <gst/base/gsttypefindhelper.h>
#include <gst/gst-i18n-plugin.h>
#include <gst/tag/tag.h>

#include "gstid3demux.h"
#include "id3tags.h"

static const GstElementDetails gst_id3demux_details =
GST_ELEMENT_DETAILS ("ID3 tag demuxer",
    "Codec/Demuxer/Metadata",
    "Read and output ID3v1 and ID3v2 tags while demuxing the contents",
    "Jan Schmidt <thaytan@mad.scientist.com>");

enum
{
  ARG_0,
  ARG_PREFER_V1
};

/* Require at least 4kB 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 */
#define ID3_TYPE_FIND_MIN_SIZE 4096
#define ID3_TYPE_FIND_MAX_SIZE 40960

GST_DEBUG_CATEGORY (id3demux_debug);
#define GST_CAT_DEFAULT (id3demux_debug)

static GstStaticPadTemplate sink_factory = GST_STATIC_PAD_TEMPLATE ("sink",
    GST_PAD_SINK,
    GST_PAD_ALWAYS,
    GST_STATIC_CAPS ("application/x-id3")
    );

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

static void gst_id3demux_class_init (GstID3DemuxClass * klass);
static void gst_id3demux_base_init (GstID3DemuxClass * klass);
static void gst_id3demux_init (GstID3Demux * id3demux);
static void gst_id3demux_dispose (GObject * object);

static void gst_id3demux_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec);
static void gst_id3demux_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec);

static GstFlowReturn gst_id3demux_chain (GstPad * pad, GstBuffer * buf);
static gboolean gst_id3demux_sink_event (GstPad * pad, GstEvent * event);
static gboolean gst_id3demux_src_activate_pull (GstPad * pad, gboolean active);
static GstFlowReturn gst_id3demux_read_range (GstID3Demux * id3demux,
    guint64 offset, guint length, GstBuffer ** buffer);

static gboolean gst_id3demux_src_checkgetrange (GstPad * srcpad);
static GstFlowReturn gst_id3demux_src_getrange (GstPad * srcpad,
    guint64 offset, guint length, GstBuffer ** buffer);

static gboolean gst_id3demux_add_srcpad (GstID3Demux * id3demux,
    GstCaps * new_caps);
static gboolean gst_id3demux_remove_srcpad (GstID3Demux * id3demux);

static gboolean gst_id3demux_srcpad_event (GstPad * pad, GstEvent * event);
static gboolean gst_id3demux_sink_activate (GstPad * sinkpad);
static GstStateChangeReturn gst_id3demux_change_state (GstElement * element,
    GstStateChange transition);
static gboolean gst_id3demux_pad_query (GstPad * pad, GstQuery * query);
static const GstQueryType *gst_id3demux_get_query_types (GstPad * pad);
static gboolean id3demux_get_upstream_size (GstID3Demux * id3demux);
static void gst_id3demux_send_tag_event (GstID3Demux * id3demux);

static GstElementClass *parent_class = NULL;

GType
gst_id3demux_get_type (void)
{
  static GType plugin_type = 0;

  if (!plugin_type) {
    static const GTypeInfo plugin_info = {
      sizeof (GstID3DemuxClass),
      (GBaseInitFunc) gst_id3demux_base_init,
      NULL,
      (GClassInitFunc) gst_id3demux_class_init,
      NULL,
      NULL,
      sizeof (GstID3Demux),
      0,
      (GInstanceInitFunc) gst_id3demux_init,
    };
    plugin_type = g_type_register_static (GST_TYPE_ELEMENT,
        "GstID3Demux", &plugin_info, 0);
  }
  return plugin_type;
}

static void
gst_id3demux_base_init (GstID3DemuxClass * klass)
{
  GstElementClass *element_class = GST_ELEMENT_CLASS (klass);

  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&src_factory));
  gst_element_class_add_pad_template (element_class,
      gst_static_pad_template_get (&sink_factory));
  gst_element_class_set_details (element_class, &gst_id3demux_details);
}

static void
gst_id3demux_class_init (GstID3DemuxClass * klass)
{
  GObjectClass *gobject_class;
  GstElementClass *gstelement_class;

  gobject_class = (GObjectClass *) klass;
  gstelement_class = (GstElementClass *) klass;

  parent_class = g_type_class_peek_parent (klass);

  gobject_class->dispose = gst_id3demux_dispose;

  gobject_class->set_property = gst_id3demux_set_property;
  gobject_class->get_property = gst_id3demux_get_property;

  gstelement_class->change_state = gst_id3demux_change_state;

  g_object_class_install_property (gobject_class, ARG_PREFER_V1,
      g_param_spec_boolean ("prefer-v1", "Prefer version 1 tag",
          "Prefer tags from ID3v1 tag at end of file when both ID3v1 "
          "and ID3v2 tags are present", FALSE,
          G_PARAM_READWRITE | G_PARAM_CONSTRUCT));
}

static void
gst_id3demux_reset (GstID3Demux * id3demux)
{
  GstBuffer **buffer_p = &id3demux->collect;
  GstCaps **caps_p = &id3demux->src_caps;

  id3demux->strip_start = 0;
  id3demux->strip_end = 0;
  id3demux->upstream_size = -1;
  id3demux->state = GST_ID3DEMUX_READID3V2;
  id3demux->send_tag_event = FALSE;

  gst_buffer_replace (buffer_p, NULL);
  gst_caps_replace (caps_p, NULL);

  gst_id3demux_remove_srcpad (id3demux);

  if (id3demux->event_tags) {
    gst_tag_list_free (id3demux->event_tags);
    id3demux->event_tags = NULL;
  }
  if (id3demux->parsed_tags) {
    gst_tag_list_free (id3demux->parsed_tags);
    id3demux->parsed_tags = NULL;
  }

}

static void
gst_id3demux_init (GstID3Demux * id3demux)
{
  GstElementClass *klass = GST_ELEMENT_GET_CLASS (id3demux);

  id3demux->sinkpad =
      gst_pad_new_from_template (gst_element_class_get_pad_template (klass,
          "sink"), "sink");
  gst_pad_set_activate_function (id3demux->sinkpad,
      GST_DEBUG_FUNCPTR (gst_id3demux_sink_activate));
  gst_pad_set_event_function (id3demux->sinkpad,
      GST_DEBUG_FUNCPTR (gst_id3demux_sink_event));
  gst_pad_set_chain_function (id3demux->sinkpad,
      GST_DEBUG_FUNCPTR (gst_id3demux_chain));
  gst_element_add_pad (GST_ELEMENT (id3demux), id3demux->sinkpad);

  id3demux->prefer_v1 = FALSE;
  gst_id3demux_reset (id3demux);
}

static void
gst_id3demux_dispose (GObject * object)
{
  GstID3Demux *id3demux = GST_ID3DEMUX (object);

  gst_id3demux_reset (id3demux);

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

static gboolean
gst_id3demux_add_srcpad (GstID3Demux * id3demux, GstCaps * new_caps)
{
  if (id3demux->src_caps == NULL ||
      !gst_caps_is_equal (new_caps, id3demux->src_caps)) {

    gst_caps_replace (&(id3demux->src_caps), new_caps);
    if (id3demux->srcpad != NULL) {
      GST_DEBUG_OBJECT (id3demux, "Changing src pad caps to %" GST_PTR_FORMAT,
          id3demux->src_caps);

      gst_pad_set_caps (id3demux->srcpad, id3demux->src_caps);
    }
  } else {
    /* Caps never changed */
    gst_caps_unref (new_caps);
  }

  if (id3demux->srcpad == NULL) {
    id3demux->srcpad = gst_pad_new_from_static_template (&src_factory, "src");
    g_return_val_if_fail (id3demux->srcpad != NULL, FALSE);

    gst_pad_set_query_type_function (id3demux->srcpad,
        GST_DEBUG_FUNCPTR (gst_id3demux_get_query_types));
    gst_pad_set_query_function (id3demux->srcpad,
        GST_DEBUG_FUNCPTR (gst_id3demux_pad_query));
    gst_pad_set_event_function (id3demux->srcpad,
        GST_DEBUG_FUNCPTR (gst_id3demux_srcpad_event));
    gst_pad_set_activatepull_function (id3demux->srcpad,
        GST_DEBUG_FUNCPTR (gst_id3demux_src_activate_pull));
    gst_pad_set_checkgetrange_function (id3demux->srcpad,
        GST_DEBUG_FUNCPTR (gst_id3demux_src_checkgetrange));
    gst_pad_set_getrange_function (id3demux->srcpad,
        GST_DEBUG_FUNCPTR (gst_id3demux_src_getrange));

    gst_pad_use_fixed_caps (id3demux->srcpad);

    if (id3demux->src_caps)
      gst_pad_set_caps (id3demux->srcpad, id3demux->src_caps);

    GST_DEBUG_OBJECT (id3demux, "Adding src pad with caps %" GST_PTR_FORMAT,
        id3demux->src_caps);

    gst_object_ref (id3demux->srcpad);
    gst_pad_set_active (id3demux->srcpad, TRUE);
    if (!(gst_element_add_pad (GST_ELEMENT (id3demux), id3demux->srcpad)))
      return FALSE;
    gst_element_no_more_pads (GST_ELEMENT (id3demux));
  }

  return TRUE;
}

static gboolean
gst_id3demux_remove_srcpad (GstID3Demux * id3demux)
{
  gboolean res = TRUE;

  if (id3demux->srcpad != NULL) {
    GST_DEBUG_OBJECT (id3demux, "Removing src pad");
    res = gst_element_remove_pad (GST_ELEMENT (id3demux), id3demux->srcpad);
    g_return_val_if_fail (res != FALSE, FALSE);
    gst_object_unref (id3demux->srcpad);
    id3demux->srcpad = NULL;
  }

  return res;
};

/* will return FALSE if buffer is beyond end of data; will return TRUE
 * if buffer was trimmed successfully or didn't need trimming, but may
 * also return TRUE and set *buf_ref to NULL if the buffer was before
 * the start of the data */
static gboolean
gst_id3demux_trim_buffer (GstID3Demux * id3demux, 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 ID3v1 tag at the end of file, trim it */
  if (id3demux->strip_end > 0) {
    if (id3demux_get_upstream_size (id3demux)) {
      guint64 v1tag_offset = id3demux->upstream_size - id3demux->strip_end;

      if (out_offset >= v1tag_offset) {
        GST_DEBUG_OBJECT (id3demux, "Buffer is past the end of the data");
        goto no_out_buffer_end;
      }

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

  if (id3demux->strip_start > 0) {
    /* If the buffer crosses the ID3v2 tag at the start of file, trim it */
    if (out_offset <= id3demux->strip_start) {
      if (out_offset + out_size <= id3demux->strip_start) {
        GST_DEBUG_OBJECT (id3demux, "Buffer is before the start of the data");
        goto no_out_buffer_start;
      }

      trim_start = id3demux->strip_start - out_offset;
      out_size -= trim_start;
      out_offset = 0;
    } else {
      out_offset -= id3demux->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 (id3demux, "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 (id3demux, "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, id3demux->src_caps);
  }

  return TRUE;

no_out_buffer_end:
  {
    gst_buffer_unref (buf);
    *buf_ref = NULL;
    return FALSE;
  }
no_out_buffer_start:
  {
    gst_buffer_unref (buf);
    *buf_ref = NULL;
    return TRUE;
  }
}

static GstFlowReturn
gst_id3demux_chain (GstPad * pad, GstBuffer * buf)
{
  GstID3Demux *id3demux;

  id3demux = GST_ID3DEMUX (GST_PAD_PARENT (pad));
  g_return_val_if_fail (GST_IS_ID3DEMUX (id3demux), GST_FLOW_ERROR);

  if (id3demux->collect == NULL) {
    id3demux->collect = buf;
  } else {
    id3demux->collect = gst_buffer_join (id3demux->collect, buf);
  }
  buf = NULL;

  switch (id3demux->state) {
    case GST_ID3DEMUX_READID3V2:
      /* 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_IS_VALID (id3demux->collect) &&
          GST_BUFFER_OFFSET (id3demux->collect) != 0) {
        GST_DEBUG_OBJECT (id3demux,
            "Received buffer with non-zero offset %" G_GINT64_FORMAT
            ". Can't read tags", GST_BUFFER_OFFSET (id3demux->collect));
      } else {
        ID3TagsResult tag_result;

        tag_result = id3demux_read_id3v2_tag (id3demux->collect,
            &id3demux->strip_start, &id3demux->parsed_tags);
        if (tag_result == ID3TAGS_MORE_DATA)
          break;                /* Go get more data and try again */
        else if (tag_result == ID3TAGS_BROKEN_TAG)
          GST_WARNING_OBJECT (id3demux,
              "Ignoring broken ID3v2 tag of size %d", id3demux->strip_start);
        else
          GST_DEBUG_OBJECT (id3demux, "Found an ID3v2 tag of size %d\n",
              id3demux->strip_start);

        id3demux->send_tag_event = TRUE;
      }
      id3demux->state = GST_ID3DEMUX_TYPEFINDING;

      /* Fall-through */
    case GST_ID3DEMUX_TYPEFINDING:{
      GstTypeFindProbability probability = 0;
      GstBuffer *typefind_buf = NULL;
      GstCaps *caps;

      if (GST_BUFFER_SIZE (id3demux->collect) <
          ID3_TYPE_FIND_MIN_SIZE + id3demux->strip_start)
        break;                  /* Go get more data first */

      GST_DEBUG_OBJECT (id3demux, "Typefinding with size %d",
          GST_BUFFER_SIZE (id3demux->collect));

      /* Trim the buffer and adjust offset for typefinding */
      typefind_buf = id3demux->collect;
      gst_buffer_ref (typefind_buf);
      if (!gst_id3demux_trim_buffer (id3demux, &typefind_buf))
        return GST_FLOW_UNEXPECTED;

      if (typefind_buf == NULL)
        break;                  /* Still need more data */

      caps = gst_type_find_helper_for_buffer (GST_OBJECT (id3demux),
          typefind_buf, &probability);

      if (caps == NULL) {
        if (GST_BUFFER_SIZE (typefind_buf) < ID3_TYPE_FIND_MAX_SIZE) {
          /* Just break for more data */
          gst_buffer_unref (typefind_buf);
          return GST_FLOW_OK;
        }

        /* We failed typefind */
        GST_ELEMENT_ERROR (id3demux, STREAM, TYPE_NOT_FOUND, (NULL),
            ("Could not detect type for contents within an ID3 tag"));
        gst_buffer_unref (typefind_buf);
        gst_buffer_unref (id3demux->collect);
        id3demux->collect = NULL;
        return GST_FLOW_ERROR;
      }

      GST_DEBUG_OBJECT (id3demux, "Found type %" GST_PTR_FORMAT " with a "
          "probability of %u, buf size was %u", caps, probability,
          GST_BUFFER_SIZE (typefind_buf));

      gst_buffer_unref (typefind_buf);

      if (!gst_id3demux_add_srcpad (id3demux, caps)) {
        GST_DEBUG_OBJECT (id3demux, "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 */
      id3demux->state = GST_ID3DEMUX_STREAMING;

      /* Now that typefinding is complete, post the
       * tags message */
      if (id3demux->parsed_tags != NULL) {
        gst_element_post_message (GST_ELEMENT (id3demux),
            gst_message_new_tag (GST_OBJECT (id3demux),
                gst_tag_list_copy (id3demux->parsed_tags)));
      }
      /* fall-through */
    }
    case GST_ID3DEMUX_STREAMING:{
      GstBuffer *outbuf = NULL;

      if (id3demux->send_tag_event) {
        gst_id3demux_send_tag_event (id3demux);
        id3demux->send_tag_event = FALSE;
      }

      /* Trim the buffer and adjust offset */
      if (id3demux->collect) {
        outbuf = id3demux->collect;
        id3demux->collect = NULL;
        if (!gst_id3demux_trim_buffer (id3demux, &outbuf))
          return GST_FLOW_UNEXPECTED;
      }
      if (outbuf) {
        if (G_UNLIKELY (id3demux->srcpad == NULL)) {
          gst_buffer_unref (outbuf);
          return GST_FLOW_ERROR;
        }

        GST_DEBUG_OBJECT (id3demux, "Pushing buffer %p", outbuf);

        /* Ensure the caps are set correctly */
        outbuf = gst_buffer_make_metadata_writable (outbuf);
        gst_buffer_set_caps (outbuf, GST_PAD_CAPS (id3demux->srcpad));

        return gst_pad_push (id3demux->srcpad, outbuf);
      }
    }
  }
  return GST_FLOW_OK;

error:
  GST_DEBUG_OBJECT (id3demux, "error in chain function");

  return GST_FLOW_ERROR;
}

static gboolean
gst_id3demux_sink_event (GstPad * pad, GstEvent * event)
{
  GstID3Demux *demux;
  gboolean ret;

  demux = GST_ID3DEMUX (gst_pad_get_parent (pad));

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_EOS:
      if (demux->srcpad == NULL) {
        GST_WARNING_OBJECT (demux, "EOS before we found a type");
        GST_ELEMENT_ERROR (demux, STREAM, TYPE_NOT_FOUND, (NULL), (NULL));
      }
      ret = gst_pad_event_default (pad, event);
      break;
    default:
      ret = gst_pad_event_default (pad, event);
      break;
  }

  gst_object_unref (demux);
  return ret;
}


static void
gst_id3demux_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
  GstID3Demux *id3demux;

  g_return_if_fail (GST_IS_ID3DEMUX (object));
  id3demux = GST_ID3DEMUX (object);

  switch (prop_id) {
    case ARG_PREFER_V1:
      id3demux->prefer_v1 = g_value_get_boolean (value);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static void
gst_id3demux_get_property (GObject * object, guint prop_id,
    GValue * value, GParamSpec * pspec)
{
  GstID3Demux *id3demux;

  g_return_if_fail (GST_IS_ID3DEMUX (object));
  id3demux = GST_ID3DEMUX (object);

  switch (prop_id) {
    case ARG_PREFER_V1:
      g_value_set_boolean (value, id3demux->prefer_v1);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static gboolean
id3demux_get_upstream_size (GstID3Demux * id3demux)
{
  GstFormat format;
  gint64 result;

  /* Short-cut if we already queried upstream */
  if (id3demux->upstream_size > 0)
    return TRUE;

  format = GST_FORMAT_BYTES;
  if (!gst_pad_query_peer_duration (id3demux->sinkpad, &format, &result) ||
      result < 0) {
    return FALSE;
  }

  id3demux->upstream_size = result;
  return TRUE;
}

static gboolean
gst_id3demux_srcpad_event (GstPad * pad, GstEvent * event)
{
  gboolean res = FALSE;
  GstID3Demux *id3demux = GST_ID3DEMUX (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 &&
          id3demux->state == GST_ID3DEMUX_STREAMING &&
          gst_pad_is_linked (id3demux->sinkpad)) {
        GstEvent *upstream;

        switch (cur_type) {
          case GST_SEEK_TYPE_SET:
            cur += id3demux->strip_start;
            break;
          case GST_SEEK_TYPE_CUR:
            break;
          case GST_SEEK_TYPE_END:
            cur += id3demux->strip_end;
            break;
          default:
            g_assert_not_reached ();
            break;
        }
        switch (stop_type) {
          case GST_SEEK_TYPE_SET:
            stop += id3demux->strip_start;
            break;
          case GST_SEEK_TYPE_CUR:
            break;
          case GST_SEEK_TYPE_END:
            stop += id3demux->strip_end;
            break;
          default:
            break;
        }
        upstream = gst_event_new_seek (rate, format, flags,
            cur_type, cur, stop_type, stop);
        res = gst_pad_push_event (id3demux->sinkpad, upstream);
      }
      break;
    }
    default:
      break;
  }

  gst_event_unref (event);
  return res;
}

/* Read and interpret any ID3v1 tag when activating in pull_range */
static gboolean
gst_id3demux_read_id3v1 (GstID3Demux * id3demux, GstTagList ** tags)
{
  GstBuffer *buffer = NULL;
  gboolean res = FALSE;
  ID3TagsResult tag_res;
  GstFlowReturn flow_ret;
  guint64 id3v1_offset;

  if (id3demux->upstream_size < ID3V1_TAG_SIZE)
    return TRUE;
  id3v1_offset = id3demux->upstream_size - ID3V1_TAG_SIZE;

  flow_ret = gst_pad_pull_range (id3demux->sinkpad, id3v1_offset,
      ID3V1_TAG_SIZE, &buffer);
  if (flow_ret != GST_FLOW_OK) {
    GST_DEBUG_OBJECT (id3demux,
        "Could not read data from start of file ret=%d", flow_ret);
    goto beach;
  }

  if (GST_BUFFER_SIZE (buffer) != ID3V1_TAG_SIZE) {
    GST_DEBUG_OBJECT (id3demux,
        "Only managed to read %u bytes from file - not an ID3 file",
        GST_BUFFER_SIZE (buffer));
    goto beach;
  }

  tag_res = id3demux_read_id3v1_tag (buffer, &id3demux->strip_end, tags);
  if (tag_res == ID3TAGS_READ_TAG) {
    GST_DEBUG_OBJECT (id3demux,
        "Read ID3v1 tag - trimming %d bytes from end of file",
        id3demux->strip_end);
    res = TRUE;
  } else if (tag_res == ID3TAGS_BROKEN_TAG) {
    GST_WARNING_OBJECT (id3demux, "Ignoring broken ID3v1 tag");
    res = TRUE;
  }
beach:
  if (buffer)
    gst_buffer_unref (buffer);
  return res;
}

/* Read and interpret any ID3v2 tag when activating in pull_range */
static gboolean
gst_id3demux_read_id3v2 (GstID3Demux * id3demux, GstTagList ** tags)
{
  GstBuffer *buffer = NULL;
  gboolean res = FALSE;
  ID3TagsResult tag_res;
  GstFlowReturn flow_ret;

  /* Handle ID3V2 tag. Try with 4kB to start with */
  flow_ret = gst_pad_pull_range (id3demux->sinkpad, 0, 4096, &buffer);
  if (flow_ret != GST_FLOW_OK) {
    GST_DEBUG_OBJECT (id3demux,
        "Could not read data from start of file ret=%d", flow_ret);
    goto beach;
  }

  if (GST_BUFFER_SIZE (buffer) < ID3V2_HDR_SIZE) {
    GST_DEBUG_OBJECT (id3demux,
        "Only managed to read %u bytes from file - not an ID3 file",
        GST_BUFFER_SIZE (buffer));
    goto beach;
  }

  tag_res = id3demux_read_id3v2_tag (buffer, &id3demux->strip_start, tags);
  if (tag_res == ID3TAGS_MORE_DATA) {
    /* Need more data to interpret the tag */
    if (buffer) {
      gst_buffer_unref (buffer);
      buffer = NULL;
    }
    g_assert (id3demux->strip_start > ID3V2_HDR_SIZE);

    GST_DEBUG_OBJECT (id3demux, "Reading %u bytes to decode ID3v2",
        id3demux->strip_start);
    flow_ret = gst_pad_pull_range (id3demux->sinkpad, 0, id3demux->strip_start,
        &buffer);
    if (flow_ret != GST_FLOW_OK) {
      GST_DEBUG_OBJECT (id3demux,
          "Could not read data from start of file ret=%d", flow_ret);
      goto beach;
    }
    tag_res = id3demux_read_id3v2_tag (buffer, &id3demux->strip_start, tags);
  }

  if (tag_res == ID3TAGS_READ_TAG) {
    res = TRUE;
    GST_DEBUG_OBJECT (id3demux, "Read ID3v2 tag of size %d",
        id3demux->strip_start);
  } else if (tag_res == ID3TAGS_BROKEN_TAG) {
    res = TRUE;
    GST_WARNING_OBJECT (id3demux, "Ignoring broken ID3v2 tag of size %d",
        id3demux->strip_start);
  }
beach:
  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_id3demux_sink_activate (GstPad * sinkpad)
{
  GstTypeFindProbability probability = 0;
  GstID3Demux *id3demux = GST_ID3DEMUX (GST_PAD_PARENT (sinkpad));
  gboolean ret = FALSE;
  GstCaps *caps = NULL;

  /* 1: */
  /* If we can activate pull_range upstream, then read any ID3v1 and ID3v2
   * tags, otherwise activate in push mode and the chain function will 
   * collect buffers, read the ID3v2 tag and output a buffer to end
   * preroll.
   */
  if (!gst_pad_check_pull_range (sinkpad) ||
      !gst_pad_activate_pull (sinkpad, TRUE)) {
    GST_DEBUG_OBJECT (id3demux,
        "No pull mode. Changing to push, but won't be able to read ID3v1 tags");
    id3demux->state = GST_ID3DEMUX_READID3V2;
    return gst_pad_activate_push (sinkpad, TRUE);
  }

  /* Look for tags at start and end of file */
  GST_DEBUG_OBJECT (id3demux, "Activated pull mode. Looking for tags");
  if (!id3demux_get_upstream_size (id3demux))
    return FALSE;

  id3demux->strip_start = 0;
  id3demux->strip_end = 0;


  if (id3demux->prefer_v1) {
    if (!gst_id3demux_read_id3v2 (id3demux, &(id3demux->parsed_tags)))
      return FALSE;
    if (!gst_id3demux_read_id3v1 (id3demux, &(id3demux->parsed_tags)))
      return FALSE;
  } else {
    if (!gst_id3demux_read_id3v1 (id3demux, &(id3demux->parsed_tags)))
      return FALSE;
    if (!gst_id3demux_read_id3v2 (id3demux, &(id3demux->parsed_tags)))
      return FALSE;
  }
  if (id3demux->parsed_tags != NULL) {
    id3demux->send_tag_event = TRUE;
  }

  /* 3 - Do typefinding on data */
  caps = gst_type_find_helper_get_range (GST_OBJECT (id3demux),
      (GstTypeFindHelperGetRangeFunction) gst_id3demux_read_range,
      id3demux->upstream_size - id3demux->strip_start - id3demux->strip_end,
      &probability);

  GST_DEBUG_OBJECT (id3demux, "Found type %" GST_PTR_FORMAT " with a "
      "probability of %u", caps, probability);

  /* 4 - Deactivate pull mode */
  if (!gst_pad_activate_pull (sinkpad, FALSE)) {
    if (caps)
      gst_caps_unref (caps);
    GST_DEBUG_OBJECT (id3demux,
        "Could not deactivate sinkpad after reading tags");
    return FALSE;
  }

  /* 5 - If we didn't find the caps, fail */
  if (caps == NULL) {
    GST_ELEMENT_ERROR (id3demux, STREAM, TYPE_NOT_FOUND, (NULL),
        ("Could not detect type for contents within an ID3 tag"));
    goto done_activate;
  }

  /* Now that we've finished typefinding, post tag message on bus */
  if (id3demux->parsed_tags != NULL) {
    gst_element_post_message (GST_ELEMENT (id3demux),
        gst_message_new_tag (GST_OBJECT (id3demux),
            gst_tag_list_copy (id3demux->parsed_tags)));
  }

  /* tag reading and typefinding were already done, don't do them again in
     the chain function if we end up in push mode */
  id3demux->state = GST_ID3DEMUX_STREAMING;

  /* 6 Add the srcpad for output now we know caps. */
  /* add_srcpad takes ownership of the caps */
  if (!gst_id3demux_add_srcpad (id3demux, caps)) {
    GST_DEBUG_OBJECT (id3demux, "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 (id3demux->srcpad, TRUE);
    ret &= gst_pad_activate_push (sinkpad, TRUE);
  }

done_activate:

  return ret;
}

static gboolean
gst_id3demux_src_activate_pull (GstPad * pad, gboolean active)
{
  GstID3Demux *id3demux = GST_ID3DEMUX (GST_PAD_PARENT (pad));

  return gst_pad_activate_pull (id3demux->sinkpad, active);
}

static gboolean
gst_id3demux_src_checkgetrange (GstPad * srcpad)
{
  GstID3Demux *id3demux = GST_ID3DEMUX (GST_PAD_PARENT (srcpad));

  return gst_pad_check_pull_range (id3demux->sinkpad);
}

static GstFlowReturn
gst_id3demux_read_range (GstID3Demux * id3demux,
    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 ID3 information. 
   * For the returned buffer, adjust the output offset to match what downstream
   * should see */
  in_offset = offset + id3demux->strip_start;

  if (!id3demux_get_upstream_size (id3demux))
    return GST_FLOW_ERROR;

  if (in_offset + length >= id3demux->upstream_size - id3demux->strip_end) {
    if (in_offset + id3demux->strip_end >= id3demux->upstream_size)
      return GST_FLOW_UNEXPECTED;
    in_length = id3demux->upstream_size - id3demux->strip_end - in_offset;
  } else {
    in_length = length;
  }

  ret = gst_pad_pull_range (id3demux->sinkpad, in_offset, in_length, buffer);
  if (ret == GST_FLOW_OK && *buffer) {
    if (!gst_id3demux_trim_buffer (id3demux, buffer))
      goto read_beyond_end;

    /* this should only happen in streaming mode */
    g_assert (*buffer != NULL);
  }

  return ret;

read_beyond_end:
  {
    GST_DEBUG_OBJECT (id3demux, "attempted read beyond end of file");
    if (*buffer != NULL) {
      gst_buffer_unref (buffer);
      *buffer = NULL;
    }
    return GST_FLOW_UNEXPECTED;
  }
}

static GstFlowReturn
gst_id3demux_src_getrange (GstPad * srcpad,
    guint64 offset, guint length, GstBuffer ** buffer)
{
  GstID3Demux *id3demux = GST_ID3DEMUX (GST_PAD_PARENT (srcpad));

  if (id3demux->send_tag_event) {
    gst_id3demux_send_tag_event (id3demux);
    id3demux->send_tag_event = FALSE;
  }
  return gst_id3demux_read_range (id3demux, offset, length, buffer);
}

static GstStateChangeReturn
gst_id3demux_change_state (GstElement * element, GstStateChange transition)
{
  GstStateChangeReturn ret;
  GstID3Demux *id3demux = GST_ID3DEMUX (element);

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

  switch (transition) {
    case GST_STATE_CHANGE_PAUSED_TO_READY:
      gst_id3demux_reset (id3demux);
      break;
    default:
      break;
  }
  return ret;
}

static gboolean
gst_id3demux_pad_query (GstPad * pad, GstQuery * query)
{
  /* For a position or duration query, adjust the returned
   * bytes to strip off the id3v1 and id3v2 areas */

  GstID3Demux *id3demux = GST_ID3DEMUX (GST_PAD_PARENT (pad));
  GstPad *peer = NULL;
  GstFormat format;
  gint64 result;

  if ((peer = gst_pad_get_peer (id3demux->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 -= id3demux->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 -= id3demux->strip_start + id3demux->strip_end;
        gst_query_set_duration (query, format, result);
      }
      break;
    }
    default:
      break;
  }

  return TRUE;
}

static const GstQueryType *
gst_id3demux_get_query_types (GstPad * pad)
{
  static const GstQueryType types[] = {
    GST_QUERY_POSITION,
    GST_QUERY_DURATION,
    0
  };

  return types;
}

static void
gst_id3demux_send_tag_event (GstID3Demux * id3demux)
{
  /* FIXME: what's the correct merge mode? Docs need to tell... */
  GstTagList *merged = gst_tag_list_merge (id3demux->event_tags,
      id3demux->parsed_tags, GST_TAG_MERGE_KEEP);

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

    GST_EVENT_TIMESTAMP (event) = 0;
    GST_DEBUG_OBJECT (id3demux, "Sending tag event on src pad");
    gst_pad_push_event (id3demux->srcpad, event);
  }
}

static gboolean
plugin_init (GstPlugin * plugin)
{
  GST_DEBUG_CATEGORY_INIT (id3demux_debug, "id3demux", 0,
      "GStreamer ID3 tag demuxer");

  gst_tag_register_musicbrainz_tags ();

  /* ensure private tag is registered */
  gst_tag_register (GST_ID3_DEMUX_TAG_ID3V2_FRAME, GST_TAG_FLAG_META,
      GST_TYPE_BUFFER, "ID3v2 frame", "unparsed id3v2 tag frame",
      gst_tag_merge_use_first);

  return gst_element_register (plugin, "id3demux",
      GST_RANK_PRIMARY, GST_TYPE_ID3DEMUX);
}

GST_PLUGIN_DEFINE (GST_VERSION_MAJOR,
    GST_VERSION_MINOR,
    "id3demux",
    "Demux ID3v1 and ID3v2 tags from a file",
    plugin_init, VERSION, GST_LICENSE, GST_PACKAGE_NAME, GST_PACKAGE_ORIGIN)