gstexiftag.c

/* GStreamer
 * Copyright (C) 2010 Thiago Santos <thiago.sousa.santos@collabora.co.uk>
 *
 * gstexiftag.c: library for reading / modifying exif tags
 *
 * 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:gsttagexif
 * @short_description: tag mappings and support functions for plugins
 *                     dealing with exif tags
 * @see_also: #GstTagList
 *
 * Contains utility function to parse #GstTagList<!-- -->s from exif
 * buffers and to create exif buffers from #GstTagList<!-- -->s
 *
 * Note that next IFD fields on the created exif buffers are set to 0.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <gst/gsttagsetter.h>
#include <gst/base/gstbytewriter.h>
#include "gsttageditingprivate.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gst/math-compat.h>

/* Some useful constants */
#define TIFF_LITTLE_ENDIAN  0x4949
#define TIFF_BIG_ENDIAN     0x4D4D
#define TIFF_HEADER_SIZE    8
#define EXIF_TAG_ENTRY_SIZE (2 + 2 + 4 + 4)

/* Exif tag types */
#define EXIF_TYPE_BYTE       1
#define EXIF_TYPE_ASCII      2
#define EXIF_TYPE_SHORT      3
#define EXIF_TYPE_LONG       4
#define EXIF_TYPE_RATIONAL   5
#define EXIF_TYPE_UNDEFINED  7
#define EXIF_TYPE_SLONG      9
#define EXIF_TYPE_SRATIONAL 10

typedef struct _GstExifTagMatch GstExifTagMatch;
typedef struct _GstExifWriter GstExifWriter;
typedef struct _GstExifReader GstExifReader;
typedef struct _GstExifTagData GstExifTagData;

typedef void (*GstExifSerializationFunc) (GstExifWriter * writer,
    const GstTagList * taglist, const GstExifTagMatch * exiftag);

/*
 * Function used to deserialize tags that don't follow the usual
 * deserialization conversions. Usually those that have 'Ref' complementary
 * tags.
 *
 * Those functions receive a exif tag data in the parameters, plus the taglist
 * and the reader and buffer if they need to get more information to build
 * its tags. There are lots of parameters, but this is needed to make it
 * versatile. Explanation of them follows:
 *
 * exif_reader: The #GstExifReader with the reading parameter and taglist for
 * results.
 * reader: The #GstByteReader pointing to the start of the next tag entry in
 * the ifd, useful for tags that use other complementary tags.
 * the buffer start
 * exiftag: The #GstExifTagMatch that contains this tag info
 * tagdata: values from the already parsed tag
 */
typedef gint (*GstExifDeserializationFunc) (GstExifReader * exif_reader,
    GstByteReader * reader, const GstExifTagMatch * exiftag,
    GstExifTagData * tagdata);

#define EXIF_SERIALIZATION_FUNC(name) \
static void serialize_ ## name (GstExifWriter * writer, \
    const GstTagList * taglist, const GstExifTagMatch * exiftag)

#define EXIF_DESERIALIZATION_FUNC(name) \
static gint deserialize_ ## name (GstExifReader * exif_reader, \
    GstByteReader * reader, const GstExifTagMatch * exiftag, \
    GstExifTagData * tagdata)

#define EXIF_SERIALIZATION_DESERIALIZATION_FUNC(name) \
  EXIF_SERIALIZATION_FUNC (name); \
  EXIF_DESERIALIZATION_FUNC (name)

/*
 * A common case among serialization/deserialization routines is that
 * the gstreamer tag is a string (with a predefined set of allowed values)
 * and exif is an int. These macros cover these cases
 */
#define EXIF_SERIALIZATION_MAP_STRING_TO_INT_FUNC(name,funcname) \
static void \
serialize_ ## name (GstExifWriter * writer, const GstTagList * taglist, \
    const GstExifTagMatch * exiftag) \
{ \
  gchar *str = NULL; \
  gint exif_value; \
\
  if (!gst_tag_list_get_string_index (taglist, exiftag->gst_tag, 0, &str)) { \
    GST_WARNING ("No %s tag present in taglist", exiftag->gst_tag); \
    return; \
  } \
\
  exif_value = __exif_tag_ ## funcname ## _to_exif_value (str); \
  if (exif_value == -1) { \
    g_free (str); \
    return; \
  } \
  g_free (str); \
\
  switch (exiftag->exif_type) { \
    case EXIF_TYPE_SHORT: \
      gst_exif_writer_write_short_tag (writer, exiftag->exif_tag, exif_value); \
      break; \
    case EXIF_TYPE_LONG: \
      gst_exif_writer_write_long_tag (writer, exiftag->exif_tag, exif_value); \
      break; \
    case EXIF_TYPE_UNDEFINED: \
    { \
        guint8 data = (guint8) exif_value; \
        write_exif_undefined_tag (writer, exiftag->exif_tag, &data, 1); \
    } \
      break; \
    default: \
      g_assert_not_reached (); \
      GST_WARNING ("Unmapped serialization for type %d", exiftag->exif_type); \
      break; \
   } \
}

#define EXIF_DESERIALIZATION_MAP_STRING_TO_INT_FUNC(name,funcname) \
static gint \
deserialize_ ## name (GstExifReader * exif_reader, \
    GstByteReader * reader, const GstExifTagMatch * exiftag, \
    GstExifTagData * tagdata) \
{ \
  const gchar *str = NULL; \
  gint value; \
\
  GST_LOG ("Starting to parse %s tag in exif 0x%x", exiftag->gst_tag, \
      exiftag->exif_tag); \
\
  /* validate tag */ \
  if (tagdata->count != 1) { \
    GST_WARNING ("0x%X has unexpected count", tagdata->count); \
    return 0; \
  } \
\
  if (tagdata->tag_type == EXIF_TYPE_SHORT) { \
    if (exif_reader->byte_order == G_LITTLE_ENDIAN) { \
      value = GST_READ_UINT16_LE (tagdata->offset_as_data); \
    } else { \
      value = GST_READ_UINT16_BE (tagdata->offset_as_data); \
    } \
  } else if (tagdata->tag_type == EXIF_TYPE_UNDEFINED) { \
    value = GST_READ_UINT8 (tagdata->offset_as_data); \
  } else { \
    GST_WARNING ("0x%X has unexpected type %d", exiftag->exif_tag, \
        tagdata->tag_type); \
    return 0; \
  } \
\
  str = __exif_tag_## funcname ## _from_exif_value (value); \
  if (str == NULL) { \
    GST_WARNING ("Invalid value for tag 0x%X: %d", tagdata->tag, value); \
    return 0; \
  } \
  gst_tag_list_add (exif_reader->taglist, GST_TAG_MERGE_REPLACE, \
      exiftag->gst_tag, str, NULL); \
\
  return 0; \
}

#define EXIF_SERIALIZATION_DESERIALIZATION_MAP_STRING_TO_INT_FUNC(name,funcname) \
  EXIF_SERIALIZATION_MAP_STRING_TO_INT_FUNC(name,funcname); \
  EXIF_DESERIALIZATION_MAP_STRING_TO_INT_FUNC(name,funcname);

struct _GstExifTagMatch
{
  const gchar *gst_tag;
  guint16 exif_tag;
  guint16 exif_type;

  /* for tags that need special handling */
  guint16 complementary_tag;
  GstExifSerializationFunc serialize;
  GstExifDeserializationFunc deserialize;
};

struct _GstExifTagData
{
  guint16 tag;
  guint16 tag_type;
  guint32 count;
  guint32 offset;
  const guint8 *offset_as_data;
};

/*
 * Holds the info and variables necessary to write
 * the exif tags properly
 */
struct _GstExifWriter
{
  GstByteWriter tagwriter;
  GstByteWriter datawriter;

  gint byte_order;
  guint tags_total;
};

struct _GstExifReader
{
  GstTagList *taglist;
  const GstBuffer *buffer;
  guint32 base_offset;
  gint byte_order;

  /* tags waiting for their complementary tags */
  GSList *pending_tags;
};

EXIF_SERIALIZATION_DESERIALIZATION_FUNC (aperture_value);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (contrast);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (exposure_program);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (exposure_mode);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (flash);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (gain_control);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (geo_coordinate);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (geo_direction);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (geo_elevation);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (metering_mode);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (orientation);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (saturation);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (scene_capture_type);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (scene_type);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (sensitivity_type);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (sharpness);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (shutter_speed);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (source);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (speed);
EXIF_SERIALIZATION_DESERIALIZATION_FUNC (white_balance);

EXIF_DESERIALIZATION_FUNC (resolution);
EXIF_DESERIALIZATION_FUNC (add_to_pending_tags);

/* FIXME copyright tag has a weird "artist\0editor\0" format that is
 * not yet handled */

/* exif tag numbers */
#define EXIF_TAG_GPS_LATITUDE_REF 0x1
#define EXIF_TAG_GPS_LATITUDE 0x2
#define EXIF_TAG_GPS_LONGITUDE_REF 0x3
#define EXIF_TAG_GPS_LONGITUDE 0x4
#define EXIF_TAG_GPS_ALTITUDE_REF 0x5
#define EXIF_TAG_GPS_ALTITUDE 0x6
#define EXIF_TAG_GPS_SPEED_REF 0xC
#define EXIF_TAG_GPS_SPEED 0xD
#define EXIF_TAG_GPS_TRACK_REF 0xE
#define EXIF_TAG_GPS_TRACK 0xF
#define EXIF_TAG_GPS_IMAGE_DIRECTION_REF 0x10
#define EXIF_TAG_GPS_IMAGE_DIRECTION 0x11
#define EXIF_TAG_GPS_HORIZONTAL_POSITIONING_ERROR 0x1F
#define EXIF_TAG_IMAGE_DESCRIPTION 0x10E
#define EXIF_TAG_MAKE 0x10F
#define EXIF_TAG_MODEL 0x110
#define EXIF_TAG_ORIENTATION 0x112
#define EXIF_TAG_XRESOLUTION 0x11A
#define EXIF_TAG_YRESOLUTION 0x11B
#define EXIF_TAG_RESOLUTION_UNIT 0x128
#define EXIF_TAG_SOFTWARE 0x131
#define EXIF_TAG_DATE_TIME 0x132
#define EXIF_TAG_ARTIST 0x13B
#define EXIF_TAG_COPYRIGHT 0x8298
#define EXIF_TAG_EXPOSURE_TIME 0x829A
#define EXIF_TAG_F_NUMBER 0x829D
#define EXIF_TAG_EXPOSURE_PROGRAM 0x8822
#define EXIF_TAG_PHOTOGRAPHIC_SENSITIVITY 0x8827
#define EXIF_TAG_SENSITIVITY_TYPE 0x8830
#define EXIF_TAG_ISO_SPEED 0x8833
#define EXIF_TAG_DATE_TIME_ORIGINAL 0x9003
#define EXIF_TAG_DATE_TIME_DIGITIZED 0x9004
#define EXIF_TAG_SHUTTER_SPEED_VALUE 0x9201
#define EXIF_TAG_APERTURE_VALUE 0x9202
#define EXIF_TAG_EXPOSURE_BIAS 0x9204
#define EXIF_TAG_METERING_MODE 0x9207
#define EXIF_TAG_FLASH 0x9209
#define EXIF_TAG_FOCAL_LENGTH 0x920A
#define EXIF_TAG_MAKER_NOTE 0x927C
#define EXIF_TAG_FILE_SOURCE 0xA300
#define EXIF_TAG_SCENE_TYPE 0xA301
#define EXIF_TAG_EXPOSURE_MODE 0xA402
#define EXIF_TAG_WHITE_BALANCE 0xA403
#define EXIF_TAG_DIGITAL_ZOOM_RATIO 0xA404
#define EXIF_TAG_SCENE_CAPTURE_TYPE 0xA406
#define EXIF_TAG_GAIN_CONTROL 0xA407
#define EXIF_TAG_CONTRAST 0xA408
#define EXIF_TAG_SATURATION 0xA409
#define EXIF_TAG_SHARPNESS 0xA40A

/* IFD pointer tags */
#define EXIF_IFD_TAG 0x8769
#define EXIF_GPS_IFD_TAG 0x8825

/* version tags */
#define EXIF_VERSION_TAG 0x9000
#define EXIF_FLASHPIX_VERSION_TAG 0xA000

/* useful macros for speed tag */
#define METERS_PER_SECOND_TO_KILOMETERS_PER_HOUR (3.6)
#define KILOMETERS_PER_HOUR_TO_METERS_PER_SECOND (1/3.6)
#define MILES_PER_HOUR_TO_METERS_PER_SECOND (0.44704)
#define KNOTS_TO_METERS_PER_SECOND (0.514444)

/*
 * Should be kept in ascending id order
 *
 * {gst-tag, exif-tag, exig-type, complementary-exif-tag, serialization-func,
 *     deserialization-func}
 */
static const GstExifTagMatch tag_map_ifd0[] = {
  {GST_TAG_IMAGE_HORIZONTAL_PPI, EXIF_TAG_XRESOLUTION, EXIF_TYPE_RATIONAL,
      0, NULL, deserialize_add_to_pending_tags},
  {GST_TAG_IMAGE_VERTICAL_PPI, EXIF_TAG_YRESOLUTION, EXIF_TYPE_RATIONAL,
      0, NULL, deserialize_add_to_pending_tags},
  {NULL, EXIF_TAG_RESOLUTION_UNIT, EXIF_TYPE_SHORT, 0, NULL,
      deserialize_resolution},
  {GST_TAG_DESCRIPTION, EXIF_TAG_IMAGE_DESCRIPTION, EXIF_TYPE_ASCII, 0, NULL,
      NULL},
  {GST_TAG_DEVICE_MANUFACTURER, EXIF_TAG_MAKE, EXIF_TYPE_ASCII, 0, NULL, NULL},
  {GST_TAG_DEVICE_MODEL, EXIF_TAG_MODEL, EXIF_TYPE_ASCII, 0, NULL, NULL},
  {GST_TAG_IMAGE_ORIENTATION, EXIF_TAG_ORIENTATION, EXIF_TYPE_SHORT, 0,
        serialize_orientation,
      deserialize_orientation},
  {GST_TAG_APPLICATION_NAME, EXIF_TAG_SOFTWARE, EXIF_TYPE_ASCII, 0, NULL, NULL},
  {GST_TAG_DATE_TIME, EXIF_TAG_DATE_TIME, EXIF_TYPE_ASCII, 0, NULL, NULL},
  {GST_TAG_ARTIST, EXIF_TAG_ARTIST, EXIF_TYPE_ASCII, 0, NULL, NULL},
  {GST_TAG_COPYRIGHT, EXIF_TAG_COPYRIGHT, EXIF_TYPE_ASCII, 0, NULL, NULL},
  {NULL, EXIF_IFD_TAG, EXIF_TYPE_LONG, 0, NULL, NULL},
  {NULL, EXIF_GPS_IFD_TAG, EXIF_TYPE_LONG, 0, NULL, NULL},
  {NULL, 0, 0, 0, NULL, NULL}
};

static const GstExifTagMatch tag_map_exif[] = {
  {GST_TAG_CAPTURING_SHUTTER_SPEED, EXIF_TAG_EXPOSURE_TIME, EXIF_TYPE_RATIONAL,
        0,
      NULL, NULL},
  {GST_TAG_CAPTURING_FOCAL_RATIO, EXIF_TAG_F_NUMBER, EXIF_TYPE_RATIONAL, 0,
        NULL,
      NULL},
  {GST_TAG_CAPTURING_EXPOSURE_PROGRAM, EXIF_TAG_EXPOSURE_PROGRAM,
        EXIF_TYPE_SHORT, 0, serialize_exposure_program,
      deserialize_exposure_program},

  /* don't need the serializer as we always write the iso speed alone */
  {GST_TAG_CAPTURING_ISO_SPEED, EXIF_TAG_PHOTOGRAPHIC_SENSITIVITY,
        EXIF_TYPE_SHORT, 0, NULL,
      deserialize_add_to_pending_tags},

  {GST_TAG_CAPTURING_ISO_SPEED, EXIF_TAG_SENSITIVITY_TYPE, EXIF_TYPE_SHORT, 0,
      serialize_sensitivity_type, deserialize_sensitivity_type},
  {GST_TAG_CAPTURING_ISO_SPEED, EXIF_TAG_ISO_SPEED, EXIF_TYPE_LONG, 0, NULL,
      NULL},
  {NULL, EXIF_VERSION_TAG, EXIF_TYPE_UNDEFINED, 0, NULL, NULL},
  {GST_TAG_DATE_TIME, EXIF_TAG_DATE_TIME_ORIGINAL, EXIF_TYPE_ASCII, 0, NULL,
      NULL},
  {GST_TAG_CAPTURING_SHUTTER_SPEED, EXIF_TAG_SHUTTER_SPEED_VALUE,
        EXIF_TYPE_SRATIONAL, 0,
      serialize_shutter_speed, deserialize_shutter_speed},
  {GST_TAG_CAPTURING_FOCAL_RATIO, EXIF_TAG_APERTURE_VALUE, EXIF_TYPE_RATIONAL,
        0,
      serialize_aperture_value, deserialize_aperture_value},
  {GST_TAG_CAPTURING_EXPOSURE_COMPENSATION, EXIF_TAG_EXPOSURE_BIAS,
      EXIF_TYPE_SRATIONAL, 0, NULL, NULL},
  {GST_TAG_CAPTURING_METERING_MODE, EXIF_TAG_METERING_MODE, EXIF_TYPE_SHORT, 0,
      serialize_metering_mode, deserialize_metering_mode},
  {GST_TAG_CAPTURING_FLASH_FIRED, EXIF_TAG_FLASH, EXIF_TYPE_SHORT, 0,
      serialize_flash, deserialize_flash},
  {GST_TAG_CAPTURING_FOCAL_LENGTH, EXIF_TAG_FOCAL_LENGTH, EXIF_TYPE_RATIONAL, 0,
      NULL, NULL},
  {GST_TAG_APPLICATION_DATA, EXIF_TAG_MAKER_NOTE, EXIF_TYPE_UNDEFINED, 0, NULL,
      NULL},
  {NULL, EXIF_FLASHPIX_VERSION_TAG, EXIF_TYPE_UNDEFINED, 0, NULL, NULL},
  {GST_TAG_CAPTURING_SOURCE, EXIF_TAG_FILE_SOURCE, EXIF_TYPE_UNDEFINED,
      0, serialize_source, deserialize_source},
  {GST_TAG_CAPTURING_SOURCE, EXIF_TAG_SCENE_TYPE, EXIF_TYPE_UNDEFINED,
      0, serialize_scene_type, deserialize_scene_type},
  {GST_TAG_CAPTURING_EXPOSURE_MODE, EXIF_TAG_EXPOSURE_MODE, EXIF_TYPE_SHORT,
      0, serialize_exposure_mode, deserialize_exposure_mode},
  {GST_TAG_CAPTURING_WHITE_BALANCE, EXIF_TAG_WHITE_BALANCE, EXIF_TYPE_SHORT,
      0, serialize_white_balance, deserialize_white_balance},
  {GST_TAG_CAPTURING_DIGITAL_ZOOM_RATIO, EXIF_TAG_DIGITAL_ZOOM_RATIO,
        EXIF_TYPE_RATIONAL, 0, NULL,
      NULL},
  {GST_TAG_CAPTURING_SCENE_CAPTURE_TYPE, EXIF_TAG_SCENE_CAPTURE_TYPE,
        EXIF_TYPE_SHORT, 0, serialize_scene_capture_type,
      deserialize_scene_capture_type},
  {GST_TAG_CAPTURING_GAIN_ADJUSTMENT, EXIF_TAG_GAIN_CONTROL,
        EXIF_TYPE_SHORT, 0, serialize_gain_control,
      deserialize_gain_control},
  {GST_TAG_CAPTURING_CONTRAST, EXIF_TAG_CONTRAST, EXIF_TYPE_SHORT, 0,
      serialize_contrast, deserialize_contrast},
  {GST_TAG_CAPTURING_SATURATION, EXIF_TAG_SATURATION, EXIF_TYPE_SHORT, 0,
      serialize_saturation, deserialize_saturation},
  {GST_TAG_CAPTURING_SHARPNESS, EXIF_TAG_SHARPNESS, EXIF_TYPE_SHORT, 0,
      serialize_sharpness, deserialize_sharpness},
  {NULL, 0, 0, 0, NULL, NULL}
};

static const GstExifTagMatch tag_map_gps[] = {
  {GST_TAG_GEO_LOCATION_LATITUDE, EXIF_TAG_GPS_LATITUDE, EXIF_TYPE_RATIONAL,
        EXIF_TAG_GPS_LATITUDE_REF,
      serialize_geo_coordinate, deserialize_geo_coordinate},
  {GST_TAG_GEO_LOCATION_LONGITUDE, EXIF_TAG_GPS_LONGITUDE, EXIF_TYPE_RATIONAL,
        EXIF_TAG_GPS_LONGITUDE_REF,
      serialize_geo_coordinate, deserialize_geo_coordinate},
  {GST_TAG_GEO_LOCATION_ELEVATION, EXIF_TAG_GPS_ALTITUDE, EXIF_TYPE_RATIONAL,
        EXIF_TAG_GPS_ALTITUDE_REF,
      serialize_geo_elevation, deserialize_geo_elevation},
  {GST_TAG_GEO_LOCATION_MOVEMENT_SPEED, EXIF_TAG_GPS_SPEED, EXIF_TYPE_RATIONAL,
        EXIF_TAG_GPS_SPEED_REF,
      serialize_speed, deserialize_speed},
  {GST_TAG_GEO_LOCATION_MOVEMENT_DIRECTION, EXIF_TAG_GPS_TRACK,
        EXIF_TYPE_RATIONAL, EXIF_TAG_GPS_TRACK_REF,
      serialize_geo_direction, deserialize_geo_direction},
  {GST_TAG_GEO_LOCATION_CAPTURE_DIRECTION, EXIF_TAG_GPS_IMAGE_DIRECTION,
        EXIF_TYPE_RATIONAL, EXIF_TAG_GPS_IMAGE_DIRECTION_REF,
      serialize_geo_direction, deserialize_geo_direction},
  {GST_TAG_GEO_LOCATION_HORIZONTAL_ERROR,
        EXIF_TAG_GPS_HORIZONTAL_POSITIONING_ERROR,
      EXIF_TYPE_RATIONAL, 0, NULL, NULL},
  {NULL, 0, 0, 0, NULL, NULL}
};

/* GstExifReader functions */
static void
gst_exif_reader_init (GstExifReader * reader, gint byte_order,
    const GstBuffer * buf, guint32 base_offset)
{
  ensure_exif_tags ();

  reader->taglist = gst_tag_list_new ();
  reader->buffer = buf;
  reader->base_offset = base_offset;
  reader->byte_order = byte_order;
  reader->pending_tags = NULL;
  if (reader->byte_order != G_LITTLE_ENDIAN &&
      reader->byte_order != G_BIG_ENDIAN) {
    GST_WARNING ("Unexpected byte order %d, using system default: %d",
        reader->byte_order, G_BYTE_ORDER);
    reader->byte_order = G_BYTE_ORDER;
  }
}

static void
gst_exif_reader_add_pending_tag (GstExifReader * reader, GstExifTagData * data)
{
  GstExifTagData *copy;

  copy = g_slice_new (GstExifTagData);
  memcpy (copy, data, sizeof (GstExifTagData));

  reader->pending_tags = g_slist_prepend (reader->pending_tags, copy);
}

static GstExifTagData *
gst_exif_reader_get_pending_tag (GstExifReader * reader, gint tagid)
{
  GSList *walker;

  for (walker = reader->pending_tags; walker; walker = g_slist_next (walker)) {
    GstExifTagData *data = (GstExifTagData *) walker->data;
    if (data->tag == tagid)
      return data;
  }

  return NULL;
}

static GstTagList *
gst_exif_reader_reset (GstExifReader * reader, gboolean return_taglist)
{
  GstTagList *ret = NULL;
  GSList *walker;

  for (walker = reader->pending_tags; walker; walker = g_slist_next (walker)) {
    GstExifTagData *data = (GstExifTagData *) walker->data;

    g_slice_free (GstExifTagData, data);
  }
  g_slist_free (reader->pending_tags);

  if (return_taglist) {
    ret = reader->taglist;
    reader->taglist = NULL;
  }

  if (reader->taglist) {
    gst_tag_list_free (reader->taglist);
  }

  return ret;
}

/* GstExifWriter functions */

static void
gst_exif_writer_init (GstExifWriter * writer, gint byte_order)
{
  ensure_exif_tags ();

  gst_byte_writer_init (&writer->tagwriter);
  gst_byte_writer_init (&writer->datawriter);

  writer->byte_order = byte_order;
  writer->tags_total = 0;
  if (writer->byte_order != G_LITTLE_ENDIAN &&
      writer->byte_order != G_BIG_ENDIAN) {
    GST_WARNING ("Unexpected byte order %d, using system default: %d",
        writer->byte_order, G_BYTE_ORDER);
    writer->byte_order = G_BYTE_ORDER;
  }
}

static GstBuffer *
gst_exif_writer_reset_and_get_buffer (GstExifWriter * writer)
{
  GstBuffer *header;
  GstBuffer *data;

  header = gst_byte_writer_reset_and_get_buffer (&writer->tagwriter);
  data = gst_byte_writer_reset_and_get_buffer (&writer->datawriter);

  return gst_buffer_join (header, data);
}

/*
 * Given the exif tag with the passed id, returns the map index of the tag
 * corresponding to it. If use_complementary is true, then the complementary
 * are also used in the search.
 *
 * Returns -1 if not found
 */
static gint
exif_tag_map_find_reverse (guint16 exif_tag, const GstExifTagMatch * tag_map,
    gboolean use_complementary)
{
  gint i;

  for (i = 0; tag_map[i].exif_tag != 0; i++) {
    if (exif_tag == tag_map[i].exif_tag || (use_complementary &&
            exif_tag == tag_map[i].complementary_tag)) {
      return i;
    }
  }
  return -1;
}

static gboolean
gst_tag_list_has_ifd_tags (const GstTagList * taglist,
    const GstExifTagMatch * tag_map)
{
  gint i;

  for (i = 0; tag_map[i].exif_tag != 0; i++) {
    if (tag_map[i].gst_tag == NULL) {
      if (tag_map[i].exif_tag == EXIF_GPS_IFD_TAG &&
          gst_tag_list_has_ifd_tags (taglist, tag_map_gps))
        return TRUE;
      if (tag_map[i].exif_tag == EXIF_IFD_TAG &&
          gst_tag_list_has_ifd_tags (taglist, tag_map_exif))
        return TRUE;
      continue;
    }

    if (gst_tag_list_get_value_index (taglist, tag_map[i].gst_tag, 0)) {
      return TRUE;
    }
  }
  return FALSE;
}

/*
 * Writes the tag entry.
 *
 * The tag entry is the tag id, the tag type,
 * the count and the offset.
 *
 * The offset is the on the amount of data writen so far, as one
 * can't predict the total bytes that the tag entries will take.
 * This means those fields requires being updated later.
 */
static void
gst_exif_writer_write_tag_header (GstExifWriter * writer,
    guint16 exif_tag, guint16 exif_type, guint32 count, guint32 offset,
    gboolean is_data)
{
  GST_DEBUG ("Writing tag entry: id %x, type %u, count %u, offset %u",
      exif_tag, exif_type, count, offset);

  if (writer->byte_order == G_LITTLE_ENDIAN) {
    gst_byte_writer_put_uint16_le (&writer->tagwriter, exif_tag);
    gst_byte_writer_put_uint16_le (&writer->tagwriter, exif_type);
    gst_byte_writer_put_uint32_le (&writer->tagwriter, count);
    gst_byte_writer_put_uint32_le (&writer->tagwriter, offset);
  } else if (writer->byte_order == G_BIG_ENDIAN) {
    gst_byte_writer_put_uint16_be (&writer->tagwriter, exif_tag);
    gst_byte_writer_put_uint16_be (&writer->tagwriter, exif_type);
    gst_byte_writer_put_uint32_be (&writer->tagwriter, count);
    if (is_data) {
      gst_byte_writer_put_uint32_le (&writer->tagwriter, offset);
    } else {
      gst_byte_writer_put_uint32_be (&writer->tagwriter, offset);
    }
  } else {
    g_assert_not_reached ();
  }

  writer->tags_total++;
}

static void
gst_exif_writer_write_rational_data (GstExifWriter * writer, guint32 frac_n,
    guint32 frac_d)
{
  if (writer->byte_order == G_LITTLE_ENDIAN) {
    gst_byte_writer_put_uint32_le (&writer->datawriter, frac_n);
    gst_byte_writer_put_uint32_le (&writer->datawriter, frac_d);
  } else {
    gst_byte_writer_put_uint32_be (&writer->datawriter, frac_n);
    gst_byte_writer_put_uint32_be (&writer->datawriter, frac_d);
  }
}

static void
gst_exif_writer_write_signed_rational_data (GstExifWriter * writer,
    gint32 frac_n, gint32 frac_d)
{
  if (writer->byte_order == G_LITTLE_ENDIAN) {
    gst_byte_writer_put_int32_le (&writer->datawriter, frac_n);
    gst_byte_writer_put_int32_le (&writer->datawriter, frac_d);
  } else {
    gst_byte_writer_put_int32_be (&writer->datawriter, frac_n);
    gst_byte_writer_put_int32_be (&writer->datawriter, frac_d);
  }
}

static void
gst_exif_writer_write_rational_tag (GstExifWriter * writer,
    guint16 tag, guint32 frac_n, guint32 frac_d)
{
  guint32 offset = gst_byte_writer_get_size (&writer->datawriter);

  gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_RATIONAL,
      1, offset, FALSE);

  gst_exif_writer_write_rational_data (writer, frac_n, frac_d);
}

static void
gst_exif_writer_write_signed_rational_tag (GstExifWriter * writer,
    guint16 tag, gint32 frac_n, gint32 frac_d)
{
  guint32 offset = gst_byte_writer_get_size (&writer->datawriter);

  gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_SRATIONAL,
      1, offset, FALSE);

  gst_exif_writer_write_signed_rational_data (writer, frac_n, frac_d);
}

static void
gst_exif_writer_write_rational_tag_from_double (GstExifWriter * writer,
    guint16 tag, gdouble value)
{
  gint frac_n;
  gint frac_d;

  gst_util_double_to_fraction (value, &frac_n, &frac_d);

  gst_exif_writer_write_rational_tag (writer, tag, frac_n, frac_d);
}

static void
gst_exif_writer_write_signed_rational_tag_from_double (GstExifWriter * writer,
    guint16 tag, gdouble value)
{
  gint frac_n;
  gint frac_d;

  gst_util_double_to_fraction (value, &frac_n, &frac_d);

  gst_exif_writer_write_signed_rational_tag (writer, tag, frac_n, frac_d);
}

static void
gst_exif_writer_write_byte_tag (GstExifWriter * writer, guint16 tag,
    guint8 value)
{
  guint32 offset = 0;

  GST_WRITE_UINT8 ((guint8 *) & offset, value);
  gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_BYTE,
      1, offset, TRUE);
}

static void
gst_exif_writer_write_short_tag (GstExifWriter * writer, guint16 tag,
    guint16 value)
{
  guint32 offset = 0;

  if (writer->byte_order == G_LITTLE_ENDIAN) {
    GST_WRITE_UINT16_LE ((guint8 *) & offset, value);
  } else {
    GST_WRITE_UINT16_BE ((guint8 *) & offset, value);
  }

  gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_SHORT,
      1, offset, TRUE);
}

static void
gst_exif_writer_write_long_tag (GstExifWriter * writer, guint16 tag,
    guint32 value)
{
  guint32 offset = 0;
  if (writer->byte_order == G_LITTLE_ENDIAN) {
    GST_WRITE_UINT32_LE ((guint8 *) & offset, value);
  } else {
    GST_WRITE_UINT32_BE ((guint8 *) & offset, value);
  }

  gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_LONG,
      1, offset, TRUE);
}


static void
write_exif_undefined_tag (GstExifWriter * writer, guint16 tag,
    const guint8 * data, gint size)
{
  guint32 offset = 0;

  if (size > 4) {
    /* we only use the data offset here, later we add up the
     * resulting tag headers offset and the base offset */
    offset = gst_byte_writer_get_size (&writer->datawriter);
    gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_UNDEFINED,
        size, offset, FALSE);
    gst_byte_writer_put_data (&writer->datawriter, data, size);
  } else {
    /* small enough to go in the offset */
    memcpy ((guint8 *) & offset, data, size);
    gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_UNDEFINED,
        size, offset, TRUE);
  }
}

static void
write_exif_ascii_tag (GstExifWriter * writer, guint16 tag, const gchar * str)
{
  gint size;
  guint32 offset = 0;

  size = strlen (str) + 1;

  if (size > 4) {
    /* we only use the data offset here, later we add up the
     * resulting tag headers offset and the base offset */
    offset = gst_byte_writer_get_size (&writer->datawriter);
    gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_ASCII,
        size, offset, FALSE);
    gst_byte_writer_put_string (&writer->datawriter, str);
  } else {
    /* small enough to go in the offset */
    memcpy ((guint8 *) & offset, str, size);
    gst_exif_writer_write_tag_header (writer, tag, EXIF_TYPE_ASCII,
        size, offset, TRUE);
  }
}

static void
write_exif_ascii_tag_from_taglist (GstExifWriter * writer,
    const GstTagList * taglist, const GstExifTagMatch * exiftag)
{
  gchar *str = NULL;
  gboolean cleanup = FALSE;
  const GValue *value;
  gint tag_size = gst_tag_list_get_tag_size (taglist, exiftag->gst_tag);

  if (tag_size != 1) {
    /* FIXME support this by serializing them with a ','? */
    GST_WARNING ("Multiple string tags not supported yet");
    return;
  }

  value = gst_tag_list_get_value_index (taglist, exiftag->gst_tag, 0);

  /* do some conversion if needed */
  switch (G_VALUE_TYPE (value)) {
    case G_TYPE_STRING:
      str = (gchar *) g_value_get_string (value);
      break;
    default:
      if (G_VALUE_TYPE (value) == GST_TYPE_DATE_TIME) {
        GstDateTime *dt = (GstDateTime *) g_value_get_boxed (value);

        if (dt == NULL) {
          GST_WARNING ("NULL datetime received");
          break;
        }

        str = g_strdup_printf ("%04d:%02d:%02d %02d:%02d:%02d",
            gst_date_time_get_year (dt), gst_date_time_get_month (dt),
            gst_date_time_get_day (dt), gst_date_time_get_hour (dt),
            gst_date_time_get_minute (dt), gst_date_time_get_second (dt));

        cleanup = TRUE;
      } else {
        GST_WARNING ("Conversion from %s to ascii string not supported",
            G_VALUE_TYPE_NAME (value));
      }
      break;
  }

  if (str == NULL)
    return;

  write_exif_ascii_tag (writer, exiftag->exif_tag, str);
  if (cleanup)
    g_free (str);
}

static void
write_exif_undefined_tag_from_taglist (GstExifWriter * writer,
    const GstTagList * taglist, const GstExifTagMatch * exiftag)
{
  const GValue *value;
  const guint8 *data = NULL;
  gint size = 0;
  gint tag_size = gst_tag_list_get_tag_size (taglist, exiftag->gst_tag);

  if (tag_size != 1) {
    GST_WARNING ("Only the first item in the taglist will be serialized");
    return;
  }

  value = gst_tag_list_get_value_index (taglist, exiftag->gst_tag, 0);

  /* do some conversion if needed */
  switch (G_VALUE_TYPE (value)) {
    case G_TYPE_STRING:
      data = (guint8 *) g_value_get_string (value);
      size = strlen ((gchar *) data);   /* no need to +1, undefined doesn't require it */
      break;
    default:
      if (G_VALUE_TYPE (value) == GST_TYPE_BUFFER) {
        GstBuffer *buf = gst_value_get_buffer (value);

        data = GST_BUFFER_DATA (buf);
        size = GST_BUFFER_SIZE (buf);
      } else {
        GST_WARNING ("Conversion from %s to raw data not supported",
            G_VALUE_TYPE_NAME (value));
      }
      break;
  }

  if (size == 0)
    return;

  write_exif_undefined_tag (writer, exiftag->exif_tag, data, size);
}

static void
write_exif_rational_tag_from_taglist (GstExifWriter * writer,
    const GstTagList * taglist, const GstExifTagMatch * exiftag)
{
  const GValue *value;
  gdouble num = 0;
  gint tag_size = gst_tag_list_get_tag_size (taglist, exiftag->gst_tag);

  if (tag_size != 1) {
    GST_WARNING ("Only the first item in the taglist will be serialized");
    return;
  }

  value = gst_tag_list_get_value_index (taglist, exiftag->gst_tag, 0);

  /* do some conversion if needed */
  switch (G_VALUE_TYPE (value)) {
    case G_TYPE_DOUBLE:
      num = g_value_get_double (value);
      gst_exif_writer_write_rational_tag_from_double (writer, exiftag->exif_tag,
          num);
      break;
    default:
      if (G_VALUE_TYPE (value) == GST_TYPE_FRACTION) {
        gst_exif_writer_write_rational_tag (writer, exiftag->exif_tag,
            gst_value_get_fraction_numerator (value),
            gst_value_get_fraction_denominator (value));
      } else {
        GST_WARNING ("Conversion from %s to rational not supported",
            G_VALUE_TYPE_NAME (value));
      }
      break;
  }
}

static void
write_exif_signed_rational_tag_from_taglist (GstExifWriter * writer,
    const GstTagList * taglist, const GstExifTagMatch * exiftag)
{
  const GValue *value;
  gdouble num = 0;
  gint tag_size = gst_tag_list_get_tag_size (taglist, exiftag->gst_tag);

  if (tag_size != 1) {
    GST_WARNING ("Only the first item in the taglist will be serialized");
    return;
  }

  value = gst_tag_list_get_value_index (taglist, exiftag->gst_tag, 0);

  /* do some conversion if needed */
  switch (G_VALUE_TYPE (value)) {
    case G_TYPE_DOUBLE:
      num = g_value_get_double (value);
      gst_exif_writer_write_signed_rational_tag_from_double (writer,
          exiftag->exif_tag, num);
      break;
    default:
      if (G_VALUE_TYPE (value) == GST_TYPE_FRACTION) {
        gst_exif_writer_write_signed_rational_tag (writer, exiftag->exif_tag,
            gst_value_get_fraction_numerator (value),
            gst_value_get_fraction_denominator (value));
      } else {
        GST_WARNING ("Conversion from %s to signed rational not supported",
            G_VALUE_TYPE_NAME (value));
      }
      break;
  }
}

static void
write_exif_integer_tag_from_taglist (GstExifWriter * writer,
    const GstTagList * taglist, const GstExifTagMatch * exiftag)
{
  const GValue *value;
  guint32 num = 0;
  gint tag_size = gst_tag_list_get_tag_size (taglist, exiftag->gst_tag);

  if (tag_size != 1) {
    GST_WARNING ("Only the first item in the taglist will be serialized");
    return;
  }

  value = gst_tag_list_get_value_index (taglist, exiftag->gst_tag, 0);

  /* do some conversion if needed */
  switch (G_VALUE_TYPE (value)) {
    case G_TYPE_INT:
      num = g_value_get_int (value);
      break;
    default:
      GST_WARNING ("Conversion from %s to int not supported",
          G_VALUE_TYPE_NAME (value));
      break;
  }

  switch (exiftag->exif_type) {
    case EXIF_TYPE_LONG:
      gst_exif_writer_write_long_tag (writer, exiftag->exif_tag, num);
      break;
    case EXIF_TYPE_SHORT:
      gst_exif_writer_write_short_tag (writer, exiftag->exif_tag, num);
      break;
    default:
      break;
  }