gstreamer/gst/gstcaps.c

/* GStreamer
 * Copyright (C) <2003> David A. Schleef <ds@schleef.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.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <string.h>
#include <signal.h>

#include "gst_private.h"
#include <gst/gst.h>

#define CAPS_POISON(caps) G_STMT_START{ \
  if (caps) { \
    GstCaps *_newcaps = gst_caps_copy (caps); \
    gst_caps_free(caps); \
    caps = _newcaps; \
  } \
} G_STMT_END
#define STRUCTURE_POISON(structure) G_STMT_START{ \
  if (structure) { \
    GstStructure *_newstruct = gst_structure_copy (structure); \
    gst_structure_free(structure); \
    structure = _newstruct; \
  } \
} G_STMT_END


static void gst_caps_transform_to_string (const GValue * src_value,
    GValue * dest_value);
static gboolean gst_caps_from_string_inplace (GstCaps * caps,
    const gchar * string);
static GstCaps *gst_caps_copy_conditional (const GstCaps * src);

GType
gst_caps_get_type (void)
{
  static GType gst_caps_type = 0;

  if (!gst_caps_type) {
    gst_caps_type = g_boxed_type_register_static ("GstCaps",
        (GBoxedCopyFunc) gst_caps_copy_conditional,
        (GBoxedFreeFunc) gst_caps_free);

    g_value_register_transform_func (gst_caps_type,
        G_TYPE_STRING, gst_caps_transform_to_string);
  }

  return gst_caps_type;
}

/* creation/deletion */

/**
 * gst_caps_new_empty:
 *
 * Creates a new #GstCaps that is empty.  That is, the returned
 * #GstCaps contains no media formats.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_new_empty (void)
{
  GstCaps *caps = g_new0 (GstCaps, 1);

  caps->type = GST_TYPE_CAPS;
  caps->structs = g_ptr_array_new ();

  return caps;
}

/**
 * gst_caps_new_any:
 *
 * Creates a new #GstCaps that indicates that it is compatible with
 * any media format.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_new_any (void)
{
  GstCaps *caps = gst_caps_new_empty ();

  caps->flags = GST_CAPS_FLAGS_ANY;

  return caps;
}

/**
 * gst_caps_new_simple:
 * @media_type: the media type of the structure
 * @fieldname: first field to set
 * @...: additional arguments
 *
 * Creates a new #GstCaps that contains one #GstStructure.  The
 * structure is defined by the arguments, which have the same format
 * as @gst_structure_new().
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_new_simple (const char *media_type, const char *fieldname, ...)
{
  GstCaps *caps;
  GstStructure *structure;
  va_list var_args;

  caps = gst_caps_new_empty ();

  va_start (var_args, fieldname);
  structure = gst_structure_new_valist (media_type, fieldname, var_args);
  va_end (var_args);

  gst_caps_append_structure (caps, structure);

  return caps;
}

/**
 * gst_caps_new_full:
 * @struct1: the first structure to add
 * @...: additional structures to add
 *
 * Creates a new #GstCaps and adds all the structures listed as
 * arguments.  The list must be NULL-terminated.  The structures
 * are not copied; the returned #GstCaps owns the structures.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_new_full (GstStructure * struct1, ...)
{
  GstCaps *caps;
  va_list var_args;

  va_start (var_args, struct1);
  caps = gst_caps_new_full_valist (struct1, var_args);
  va_end (var_args);

  return caps;
}

/**
 * gst_caps_new_full_valist:
 * @structure: the first structure to add
 * @var_args: additional structures to add
 *
 * Creates a new #GstCaps and adds all the structures listed as
 * arguments.  The list must be NULL-terminated.  The structures
 * are not copied; the returned #GstCaps owns the structures.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_new_full_valist (GstStructure * structure, va_list var_args)
{
  GstCaps *caps;

  caps = gst_caps_new_empty ();

  while (structure) {
    gst_caps_append_structure (caps, structure);
    structure = va_arg (var_args, GstStructure *);
  }

  return caps;
}

/**
 * gst_caps_copy:
 * @caps: the #GstCaps to copy
 *
 * Deeply copies a #GstCaps, including all structures and all the
 * structures' values.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_copy (const GstCaps * caps)
{
  GstCaps *newcaps;
  GstStructure *structure;
  int i;

  g_return_val_if_fail (GST_IS_CAPS (caps), NULL);

  newcaps = gst_caps_new_empty ();
  newcaps->flags = caps->flags;

  for (i = 0; i < caps->structs->len; i++) {
    structure = gst_caps_get_structure (caps, i);
    gst_caps_append_structure (newcaps, gst_structure_copy (structure));
  }

  if (caps->preferred) {
    newcaps->preferred = gst_structure_copy (caps->preferred);
  }

  return newcaps;
}

/**
 * gst_caps_free:
 * @caps: the #GstCaps to free
 *
 * Frees a #GstCaps and all its structures and the structures'
 * values.
 */
void
gst_caps_free (GstCaps * caps)
{
  GstStructure *structure;
  int i;

  g_return_if_fail (GST_IS_CAPS (caps));

  if (caps->preferred) {
    gst_structure_free (caps->preferred);
  }
  for (i = 0; i < caps->structs->len; i++) {
    structure = gst_caps_get_structure (caps, i);
    gst_structure_free (structure);
  }
  g_ptr_array_free (caps->structs, TRUE);
#ifdef USE_POISONING
  memset (caps, 0xff, sizeof (GstCaps));
#endif
  g_free (caps);
}

/**
 * gst_static_caps_get:
 * @static_caps: the #GstStaticCaps to convert
 *
 * Converts a #GstStaticCaps to a #GstCaps.
 *
 * Returns: the new #GstCaps
 */
const GstCaps *
gst_static_caps_get (GstStaticCaps * static_caps)
{
  GstCaps *caps = (GstCaps *) static_caps;
  gboolean ret;

  if (caps->type == 0) {
    caps->type = GST_TYPE_CAPS;
    caps->structs = g_ptr_array_new ();
    ret = gst_caps_from_string_inplace (caps, static_caps->string);

    if (!ret) {
      g_critical ("Could not convert static caps \"%s\"", static_caps->string);
    }
  }

  return caps;
}

/* manipulation */

/**
 * gst_caps_append:
 * @caps1: the #GstCaps that will be appended to
 * @caps2: the #GstCaps to append
 *
 * Appends the structures contained in @caps2 to @caps1.  The structures
 * in @caps2 are not copied -- they are transferred to @caps1, and then
 * @caps2 is freed.
 */
void
gst_caps_append (GstCaps * caps1, GstCaps * caps2)
{
  GstStructure *structure;
  int i;

  g_return_if_fail (GST_IS_CAPS (caps1));
  g_return_if_fail (GST_IS_CAPS (caps2));

#ifdef USE_POISONING
  CAPS_POISON (caps2);
#endif
  if (gst_caps_is_any (caps1) || gst_caps_is_any (caps2)) {
    /* FIXME: this leaks */
    caps1->flags |= GST_CAPS_FLAGS_ANY;
    for (i = 0; i < caps2->structs->len; i++) {
      structure = gst_caps_get_structure (caps2, i);
      gst_structure_remove_all_fields (structure);
    }
  } else {
    for (i = 0; i < caps2->structs->len; i++) {
      structure = gst_caps_get_structure (caps2, i);
      gst_caps_append_structure (caps1, structure);
    }
  }

  if (caps2->preferred) {
    if (caps1->preferred) {
      gst_structure_free (caps2->preferred);
    } else {
      caps1->preferred = caps2->preferred;
    }
  }

  g_ptr_array_free (caps2->structs, TRUE);
#ifdef USE_POISONING
  memset (caps2, 0xff, sizeof (GstCaps));
#endif
  g_free (caps2);
}

/**
 * gst_caps_append_structure:
 * @caps: the #GstCaps that will be appended to
 * @structure: the #GstStructure to append
 *
 * Appends @structure to @caps.  The structure is not copied; @caps
 * becomes the owner of @structure.
 */
void
gst_caps_append_structure (GstCaps * caps, GstStructure * structure)
{
  g_return_if_fail (GST_IS_CAPS (caps));

  if (structure) {
#if 0
#ifdef USE_POISONING
    STRUCTURE_POISON (structure);
#endif
#endif
    g_ptr_array_add (caps->structs, structure);
  }
}

static GstStructure *
gst_caps_remove_and_get_structure (GstCaps * caps, guint idx)
{
  /* don't use index_fast, gst_caps_simplify relies on the order */
  return g_ptr_array_remove_index (caps->structs, idx);
}

/*
 * gst_caps_remove_structure:
 * @caps: the #GstCaps to remove from
 * @idx: Index of the structure to remove
 *
 * removes the stucture with the given index from the list of structures 
 * contained in @caps.
 */
void
gst_caps_remove_structure (GstCaps * caps, guint idx)
{
  GstStructure *structure;

  g_return_if_fail (caps != NULL);
  g_return_if_fail (idx <= gst_caps_get_size (caps));

  structure = gst_caps_remove_and_get_structure (caps, idx);
  gst_structure_free (structure);
}

/**
 * gst_caps_split_one:
 * @caps: 
 *
 * This function is not implemented.
 *
 * Returns:
 */
GstCaps *
gst_caps_split_one (GstCaps * caps)
{
  /* FIXME */
  g_critical ("unimplemented");

  return NULL;
}

/**
 * gst_caps_get_size:
 * @caps: a #GstCaps
 *
 * Gets the number of structures contained in @caps.
 *
 * Returns: the number of structures that @caps contains
 */
int
gst_caps_get_size (const GstCaps * caps)
{
  g_return_val_if_fail (GST_IS_CAPS (caps), 0);

  return caps->structs->len;
}

/**
 * gst_caps_get_structure:
 * @caps: a #GstCaps
 * @index: the index of the structure
 *
 * Finds the structure in @caps that has the index @index, and 
 * returns it.
 *
 * WARNING: This function takes a const GstCaps *, but returns a
 * non-const GstStructure *.  This is for programming convenience --
 * the caller should be aware that structures inside a constant
 * @GstCaps should not be modified.
 *
 * Returns: a pointer to the #GstStructure corresponding to @index
 */
GstStructure *
gst_caps_get_structure (const GstCaps * caps, int index)
{
  g_return_val_if_fail (GST_IS_CAPS (caps), NULL);
  g_return_val_if_fail (index >= 0, NULL);
  g_return_val_if_fail (index < caps->structs->len, NULL);

  return g_ptr_array_index (caps->structs, index);
}

/**
 * gst_caps_copy_1:
 * @caps: the @GstCaps to copy
 *
 * Creates a new @GstCaps and appends a copy of the first structure
 * contained in @caps.
 *
 * Returns: the new @GstCaps
 */
GstCaps *
gst_caps_copy_1 (const GstCaps * caps)
{
  GstCaps *newcaps;
  GstStructure *structure;

  g_return_val_if_fail (GST_IS_CAPS (caps), NULL);

  newcaps = gst_caps_new_empty ();
  newcaps->flags = caps->flags;

  if (caps->structs->len > 0) {
    structure = gst_caps_get_structure (caps, 0);
    gst_caps_append_structure (newcaps, gst_structure_copy (structure));
  }

  if (caps->preferred) {
    newcaps->preferred = gst_structure_copy (caps->preferred);
  }

  return newcaps;
}

/**
 * gst_caps_set_simple:
 * @caps: the @GstCaps to set
 * @field: first field to set
 * @...: additional parameters
 *
 * Sets fields in a simple #GstCaps.  A simple #GstCaps is one that
 * only has one structure.  The arguments must be passed in the same
 * manner as @gst_structure_set(), and be NULL-terminated.
 */
void
gst_caps_set_simple (GstCaps * caps, char *field, ...)
{
  GstStructure *structure;
  va_list var_args;

  g_return_if_fail (GST_IS_CAPS (caps));
  g_return_if_fail (caps->structs->len == 1);

  structure = gst_caps_get_structure (caps, 0);

  va_start (var_args, field);
  gst_structure_set_valist (structure, field, var_args);
  va_end (var_args);
}

/**
 * gst_caps_set_simple_valist:
 * @caps: the @GstCaps to copy
 * @field: first field to set
 * @varargs: additional parameters
 *
 * Sets fields in a simple #GstCaps.  A simple #GstCaps is one that
 * only has one structure.  The arguments must be passed in the same
 * manner as @gst_structure_set(), and be NULL-terminated.
 */
void
gst_caps_set_simple_valist (GstCaps * caps, char *field, va_list varargs)
{
  GstStructure *structure;

  g_return_if_fail (GST_IS_CAPS (caps));
  g_return_if_fail (caps->structs->len != 1);

  structure = gst_caps_get_structure (caps, 0);

  gst_structure_set_valist (structure, field, varargs);
}

/* tests */

/**
 * gst_caps_is_any:
 * @caps: the @GstCaps to test
 *
 * Determines if @caps represents any media format.
 *
 * Returns: TRUE if @caps represents any format.
 */
gboolean
gst_caps_is_any (const GstCaps * caps)
{
  g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);

  return (caps->flags & GST_CAPS_FLAGS_ANY);
}

/**
 * gst_caps_is_empty:
 * @caps: the @GstCaps to test
 *
 * Determines if @caps represents no media formats.
 *
 * Returns: TRUE if @caps represents no formats.
 */
gboolean
gst_caps_is_empty (const GstCaps * caps)
{
  g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);

  if (caps->flags & GST_CAPS_FLAGS_ANY)
    return FALSE;

  return (caps->structs == NULL) || (caps->structs->len == 0);
}

/**
 * gst_caps_is_chained:
 * @caps: the @GstCaps to test
 *
 * Determines if @caps contains multiple #GstStructures.
 *
 * This function is deprecated, and should not be used in new code.
 * Use #gst_caps_is_simple() instead.
 *
 * Returns: TRUE if @caps contains more than one structure
 */
gboolean
gst_caps_is_chained (const GstCaps * caps)
{
  g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);

  return (caps->structs->len > 1);
}

static gboolean
gst_caps_is_fixed_foreach (GQuark field_id, GValue * value, gpointer unused)
{
  GType type = G_VALUE_TYPE (value);

  return gst_type_is_fixed (type);
}

/**
 * gst_caps_is_fixed:
 * @caps: the @GstCaps to test
 *
 * Fixed @GstCaps describe exactly one format, that is, they have exactly
 * one structure, and each field in the structure describes a fixed type.
 * Examples of non-fixed types are GST_TYPE_INT_RANGE and GST_TYPE_LIST.
 *
 * Returns: TRUE if @caps is fixed
 */
gboolean
gst_caps_is_fixed (const GstCaps * caps)
{
  GstStructure *structure;

  g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);

  if (caps->structs->len != 1)
    return FALSE;

  structure = gst_caps_get_structure (caps, 0);

  return gst_structure_foreach (structure, gst_caps_is_fixed_foreach, NULL);
}

static gboolean
gst_structure_is_equal_foreach (GQuark field_id, GValue * val2, gpointer data)
{
  GstStructure *struct1 = (GstStructure *) data;
  const GValue *val1 = gst_structure_id_get_value (struct1, field_id);

  if (val1 == NULL)
    return FALSE;
  if (gst_value_compare (val1, val2) == GST_VALUE_EQUAL) {
    return TRUE;
  }

  return FALSE;
}

/**
 * gst_caps_is_equal_fixed:
 * @caps1: the #GstCaps to test
 * @caps2: the #GstCaps to test
 *
 * Tests if two #GstCaps are equal.  This function only works on fixed
 * #GstCaps.
 *
 * Returns: TRUE if the arguments represent the same format
 */
gboolean
gst_caps_is_equal_fixed (const GstCaps * caps1, const GstCaps * caps2)
{
  GstStructure *struct1, *struct2;

  g_return_val_if_fail (gst_caps_is_fixed (caps1), FALSE);
  g_return_val_if_fail (gst_caps_is_fixed (caps2), FALSE);

  struct1 = gst_caps_get_structure (caps1, 0);
  struct2 = gst_caps_get_structure (caps2, 0);

  if (struct1->name != struct2->name) {
    return FALSE;
  }
  if (struct1->fields->len != struct2->fields->len) {
    return FALSE;
  }

  return gst_structure_foreach (struct1, gst_structure_is_equal_foreach,
      struct2);
}

/**
 * gst_caps_is_always_compatible:
 * @caps1: the #GstCaps to test
 * @caps2: the #GstCaps to test
 *
 * A given #GstCaps structure is always compatible with another if
 * every media format that is in the first is also contained in the
 * second.  That is, @caps1 is a subset of @caps2.
 *
 * Returns: TRUE if @caps1 is a subset of @caps2.
 */
gboolean
gst_caps_is_always_compatible (const GstCaps * caps1, const GstCaps * caps2)
{
  g_return_val_if_fail (GST_IS_CAPS (caps1), FALSE);
  g_return_val_if_fail (GST_IS_CAPS (caps2), FALSE);

  return gst_caps_is_subset (caps1, caps2);
}

/**
 * gst_caps_is_subset:
 * @subset: a #GstCaps
 * @superset: a potentially greater #GstCaps
 *
 * Checks if all caps represented by @subset are also represented by @superset
 * <note>This function does not work reliably if optional properties for caps
 * are included on one caps and omitted on the other.</note>
 *
 * Returns: TRUE if @subset is a subset of @superset
 */
gboolean
gst_caps_is_subset (const GstCaps * subset, const GstCaps * superset)
{
  GstCaps *caps;
  gboolean ret;

  g_return_val_if_fail (subset != NULL, FALSE);
  g_return_val_if_fail (superset != NULL, FALSE);

  if (gst_caps_is_empty (subset) || gst_caps_is_any (superset))
    return TRUE;
  if (gst_caps_is_any (subset) || gst_caps_is_empty (superset))
    return FALSE;

  caps = gst_caps_subtract (subset, superset);
  ret = gst_caps_is_empty (caps);
  gst_caps_free (caps);
  return ret;
}

/**
 * gst_caps_is_equal:
 * @caps1: a #GstCaps
 * @caps2: another #GstCaps
 *
 * Checks if the given caps represent the same set of caps.
 * <note>This function does not work reliably if optional properties for caps
 * are included on one caps and omitted on the other.</note>
 *
 * Returns: TRUE if both caps are equal
 */
gboolean
gst_caps_is_equal (const GstCaps * caps1, const GstCaps * caps2)
{
  g_return_val_if_fail (caps1 != NULL, FALSE);
  g_return_val_if_fail (caps2 != NULL, FALSE);

  if (gst_caps_is_fixed (caps1) && gst_caps_is_fixed (caps2))
    return gst_caps_is_equal_fixed (caps1, caps2);

  return gst_caps_is_subset (caps1, caps2) && gst_caps_is_subset (caps2, caps1);
}

typedef struct
{
  GstStructure *dest;
  const GstStructure *intersect;
  gboolean first_run;
}
IntersectData;

static gboolean
gst_caps_structure_intersect_field (GQuark id, GValue * val1, gpointer data)
{
  IntersectData *idata = (IntersectData *) data;
  GValue dest_value = { 0 };
  const GValue *val2 = gst_structure_id_get_value (idata->intersect, id);

  if (val2 == NULL) {
    gst_structure_id_set_value (idata->dest, id, val1);
  } else if (idata->first_run) {
    if (gst_value_intersect (&dest_value, val1, val2)) {
      gst_structure_id_set_value (idata->dest, id, &dest_value);
      g_value_unset (&dest_value);
    } else {
      return FALSE;
    }
  }

  return TRUE;
}

static GstStructure *
gst_caps_structure_intersect (const GstStructure * struct1,
    const GstStructure * struct2)
{
  IntersectData data;

  g_return_val_if_fail (struct1 != NULL, NULL);
  g_return_val_if_fail (struct2 != NULL, NULL);

  if (struct1->name != struct2->name)
    return NULL;

  data.dest = gst_structure_id_empty_new (struct1->name);
  data.intersect = struct2;
  data.first_run = TRUE;
  if (!gst_structure_foreach ((GstStructure *) struct1,
          gst_caps_structure_intersect_field, &data))
    goto error;

  data.intersect = struct1;
  data.first_run = FALSE;
  if (!gst_structure_foreach ((GstStructure *) struct2,
          gst_caps_structure_intersect_field, &data))
    goto error;

  return data.dest;

error:
  gst_structure_free (data.dest);
  return NULL;
}

#if 0
static GstStructure *
gst_caps_structure_union (const GstStructure * struct1,
    const GstStructure * struct2)
{
  int i;
  GstStructure *dest;
  const GstStructureField *field1;
  const GstStructureField *field2;
  int ret;

  /* FIXME this doesn't actually work */

  if (struct1->name != struct2->name)
    return NULL;

  dest = gst_structure_id_empty_new (struct1->name);

  for (i = 0; i < struct1->fields->len; i++) {
    GValue dest_value = { 0 };

    field1 = GST_STRUCTURE_FIELD (struct1, i);
    field2 = gst_structure_id_get_field (struct2, field1->name);

    if (field2 == NULL) {
      continue;
    } else {
      if (gst_value_union (&dest_value, &field1->value, &field2->value)) {
        gst_structure_set_value (dest, g_quark_to_string (field1->name),
            &dest_value);
      } else {
        ret = gst_value_compare (&field1->value, &field2->value);
      }
    }
  }

  return dest;
}
#endif

/* operations */

/**
 * gst_caps_intersect:
 * @caps1: a #GstCaps to intersect
 * @caps2: a #GstCaps to intersect
 *
 * Creates a new #GstCaps that contains all the formats that are common
 * to both @caps1 and @caps2.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_intersect (const GstCaps * caps1, const GstCaps * caps2)
{
  int i, j;
  GstStructure *struct1;
  GstStructure *struct2;
  GstCaps *dest;

  g_return_val_if_fail (GST_IS_CAPS (caps1), NULL);
  g_return_val_if_fail (GST_IS_CAPS (caps2), NULL);

  if (gst_caps_is_empty (caps1) || gst_caps_is_empty (caps2)) {
    return gst_caps_new_empty ();
  }
  if (gst_caps_is_any (caps1))
    return gst_caps_copy (caps2);
  if (gst_caps_is_any (caps2))
    return gst_caps_copy (caps1);

  dest = gst_caps_new_empty ();
  for (i = 0; i < caps1->structs->len; i++) {
    struct1 = gst_caps_get_structure (caps1, i);
    for (j = 0; j < caps2->structs->len; j++) {
      GstStructure *istruct;

      struct2 = gst_caps_get_structure (caps2, j);
      istruct = gst_caps_structure_intersect (struct1, struct2);

      gst_caps_append_structure (dest, istruct);
    }
  }

  if (caps1->preferred) {
    dest->preferred = gst_structure_copy (caps1->preferred);
  } else if (caps2->preferred) {
    dest->preferred = gst_structure_copy (caps2->preferred);
  }

  gst_caps_do_simplify (dest);
  return dest;
}

typedef struct
{
  const GstStructure *subtract_from;
  GSList *put_into;
}
SubtractionEntry;


gboolean
gst_caps_structure_subtract_field (GQuark field_id, GValue * value,
    gpointer user_data)
{
  SubtractionEntry *e = user_data;
  GValue subtraction = { 0, };
  const GValue *other;
  GstStructure *structure;

  other = gst_structure_id_get_value (e->subtract_from, field_id);
  if (!other) {
    return FALSE;
  }
  if (!gst_value_subtract (&subtraction, other, value))
    return TRUE;
  if (gst_value_compare (&subtraction, other) == GST_VALUE_EQUAL) {
    g_value_unset (&subtraction);
    return FALSE;
  } else {
    structure = gst_structure_copy (e->subtract_from);
    gst_structure_id_set_value (structure, field_id, &subtraction);
    g_value_unset (&subtraction);
    e->put_into = g_slist_prepend (e->put_into, structure);
    return TRUE;
  }
}

static gboolean
gst_caps_structure_subtract (GSList ** into, const GstStructure * minuend,
    const GstStructure * subtrahend)
{
  SubtractionEntry e;
  gboolean ret;

  e.subtract_from = minuend;
  e.put_into = NULL;

  ret = gst_structure_foreach ((GstStructure *) subtrahend,
      gst_caps_structure_subtract_field, &e);
  if (ret) {
    *into = e.put_into;
  } else {
    GSList *walk;

    for (walk = e.put_into; walk; walk = g_slist_next (walk)) {
      gst_structure_free (walk->data);
    }
    g_slist_free (e.put_into);
  }
  return ret;
}

/**
 * gst_caps_subtract:
 * @minuend: #GstCaps to substract from
 * @subtrahend: #GstCaps to substract
 *
 * Subtracts the @subtrahend from the @minuend.
 * <note>This function does not work reliably if optional properties for caps
 * are included on one caps and omitted on the other.</note>
 *
 * Returns: the resulting caps
 */
GstCaps *
gst_caps_subtract (const GstCaps * minuend, const GstCaps * subtrahend)
{
  int i, j;
  GstStructure *min;
  GstStructure *sub;
  GstCaps *dest = NULL, *src;

  g_return_val_if_fail (minuend != NULL, NULL);
  g_return_val_if_fail (subtrahend != NULL, NULL);

  if (gst_caps_is_empty (minuend) || gst_caps_is_any (subtrahend)) {
    return gst_caps_new_empty ();
  }
  if (gst_caps_is_empty (subtrahend))
    return gst_caps_copy (minuend);

  /* FIXME: Do we want this here or above?
     The reason we need this is that there is no definition about what
     ANY means for specific types, so it's not possible to reduce ANY partially
     You can only remove everything or nothing and that is done above.
     Note: there's a test that checks this behaviour. */
  g_return_val_if_fail (!gst_caps_is_any (minuend), NULL);
  g_assert (subtrahend->structs->len > 0);

  src = gst_caps_copy (minuend);
  for (i = 0; i < subtrahend->structs->len; i++) {
    sub = gst_caps_get_structure (subtrahend, i);
    if (dest) {
      gst_caps_free (src);
      src = dest;
    }
    dest = gst_caps_new_empty ();
    for (j = 0; j < src->structs->len; j++) {
      min = gst_caps_get_structure (src, j);
      if (gst_structure_get_name_id (min) == gst_structure_get_name_id (sub)) {
        GSList *list;

        if (gst_caps_structure_subtract (&list, min, sub)) {
          GSList *walk;

          for (walk = list; walk; walk = g_slist_next (walk)) {
            gst_caps_append_structure (dest, (GstStructure *) walk->data);
          }
          g_slist_free (list);
        } else {
          gst_caps_append_structure (dest, gst_structure_copy (min));
        }
      } else {
        gst_caps_append_structure (dest, gst_structure_copy (min));
      }
    }
    if (gst_caps_is_empty (dest)) {
      gst_caps_free (src);
      return dest;
    }
  }

  gst_caps_free (src);
  gst_caps_do_simplify (dest);
  return dest;
}

/**
 * gst_caps_union:
 * @caps1: a #GstCaps to union
 * @caps2: a #GstCaps to union
 *
 * Creates a new #GstCaps that contains all the formats that are in
 * either @caps1 and @caps2.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_union (const GstCaps * caps1, const GstCaps * caps2)
{
  GstCaps *dest1;
  GstCaps *dest2;

  if (gst_caps_is_any (caps1) || gst_caps_is_any (caps2))
    return gst_caps_new_any ();

  dest1 = gst_caps_copy (caps1);
  dest2 = gst_caps_copy (caps2);
  gst_caps_append (dest1, dest2);

  if (caps1->preferred) {
    dest1->preferred = gst_structure_copy (caps1->preferred);
  } else if (caps2->preferred) {
    dest1->preferred = gst_structure_copy (caps2->preferred);
  }

  gst_caps_do_simplify (dest1);
  return dest1;
}

typedef struct _NormalizeForeach
{
  GstCaps *caps;
  GstStructure *structure;
}
NormalizeForeach;

static gboolean
gst_caps_normalize_foreach (GQuark field_id, GValue * value, gpointer ptr)
{
  NormalizeForeach *nf = (NormalizeForeach *) ptr;
  GValue val = { 0 };
  int i;

  if (G_VALUE_TYPE (value) == GST_TYPE_LIST) {
    for (i = 1; i < gst_value_list_get_size (value); i++) {
      const GValue *v = gst_value_list_get_value (value, i);
      GstStructure *structure = gst_structure_copy (nf->structure);

      gst_structure_id_set_value (structure, field_id, v);
      gst_caps_append_structure (nf->caps, structure);
    }

    gst_value_init_and_copy (&val, gst_value_list_get_value (value, 0));
    gst_structure_id_set_value (nf->structure, field_id, &val);
    g_value_unset (&val);

    return FALSE;
  }
  return TRUE;
}

/**
 * gst_caps_normalize:
 * @caps: a #GstCaps to normalize
 *
 * Creates a new #GstCaps that represents the same set of formats as
 * @caps, but contains no lists.  Each list is expanded into separate
 * @GstStructures.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_normalize (const GstCaps * caps)
{
  NormalizeForeach nf;
  GstCaps *newcaps;
  int i;

  g_return_val_if_fail (GST_IS_CAPS (caps), NULL);

  newcaps = gst_caps_copy (caps);
  nf.caps = newcaps;

  for (i = 0; i < newcaps->structs->len; i++) {
    nf.structure = gst_caps_get_structure (newcaps, i);

    while (!gst_structure_foreach (nf.structure,
            gst_caps_normalize_foreach, &nf));
  }

  return newcaps;
}

static gint
gst_caps_compare_structures (gconstpointer one, gconstpointer two)
{
  gint ret;
  const GstStructure *struct1 = *((const GstStructure **) one);
  const GstStructure *struct2 = *((const GstStructure **) two);

  /* FIXME: this orders aphabetically, but ordering the quarks might be faster 
     So what's the best way? */
  ret = strcmp (gst_structure_get_name (struct1),
      gst_structure_get_name (struct2));
  if (ret)
    return ret;

  return gst_structure_n_fields (struct2) - gst_structure_n_fields (struct1);
}

/**
 * gst_caps_simplify:
 * @caps: a #GstCaps to simplify
 *
 * Creates a new #GstCaps that represents the same set of formats as
 * @caps, but simpler.  Component structures that are identical are
 * merged.  Component structures that have ranges or lists that can
 * be merged are also merged.
 *
 * Returns: the new #GstCaps
 */
GstCaps *
gst_caps_simplify (const GstCaps * caps)
{
  GstCaps *ret;

  g_return_val_if_fail (caps != NULL, NULL);

  ret = gst_caps_copy (caps);
  gst_caps_do_simplify (ret);

  return ret;
}

typedef struct
{
  GQuark name;
  GValue value;
  GstStructure *compare;
}
UnionField;

static gboolean
gst_caps_structure_figure_out_union (GQuark field_id, GValue * value,
    gpointer user_data)
{
  UnionField *u = user_data;
  const GValue *val = gst_structure_id_get_value (u->compare, field_id);

  if (!val) {
    if (u->name)
      g_value_unset (&u->value);
    return FALSE;
  }
  if (gst_value_compare (val, value) == GST_VALUE_EQUAL)
    return TRUE;
  if (u->name) {
    g_value_unset (&u->value);
    return FALSE;
  }
  u->name = field_id;
  gst_value_union (&u->value, val, value);
  return TRUE;
}

static gboolean
gst_caps_structure_simplify (GstStructure ** result,
    const GstStructure * simplify, GstStructure * compare)
{
  GSList *list;
  UnionField field = { 0, {0,}, NULL };

  /* try to subtract to get a real subset */
  if (gst_caps_structure_subtract (&list, simplify, compare)) {
    switch (g_slist_length (list)) {
      case 0:
        *result = NULL;
        return TRUE;
      case 1:
        *result = list->data;
        g_slist_free (list);
        return TRUE;
      default:
      {
        GSList *walk;

        for (walk = list; walk; walk = g_slist_next (walk)) {
          gst_structure_free (walk->data);
        }
        g_slist_free (list);
        break;
      }
    }
  }

  /* try to union both structs */
  field.compare = compare;
  if (gst_structure_foreach ((GstStructure *) simplify,
          gst_caps_structure_figure_out_union, &field)) {
    gboolean ret = FALSE;

    /* now we know all of simplify's fields are the same in compare
     * but at most one field: field.name */
    if (G_IS_VALUE (&field.value)) {
      if (gst_structure_n_fields (simplify) == gst_structure_n_fields (compare)) {
        gst_structure_id_set_value (compare, field.name, &field.value);
        *result = NULL;
        ret = TRUE;
      }
      g_value_unset (&field.value);
    } else if (gst_structure_n_fields (simplify) <=
        gst_structure_n_fields (compare)) {
      /* compare is just more specific, will be optimized away later */
      /* FIXME: do this here? */
      GST_LOG ("found a case that will be optimized later.");
    } else {
      gchar *one = gst_structure_to_string (simplify);
      gchar *two = gst_structure_to_string (compare);

      GST_ERROR
          ("caps mismatch: structures %s and %s claim to be possible to unify, but aren't",
          one, two);
      g_free (one);
      g_free (two);
    }
    return ret;
  }

  return FALSE;
}

/**
 * gst_caps_do_simplify:
 * @caps: a #GstCaps to simplify
 *
 * Modifies the given @caps inplace into a representation that represents the 
 * same set of formats, but in a simpler form.  Component structures that are 
 * identical are merged.  Component structures that have values that can be 
 * merged are also merged.
 *
 * Returns: TRUE, if the caps could be simplified
 */
gboolean
gst_caps_do_simplify (GstCaps * caps)
{
  GstStructure *simplify, *compare, *result;
  gint i, j, start;
  gboolean changed = FALSE;

  g_return_val_if_fail (caps != NULL, FALSE);

  if (gst_caps_get_size (caps) < 2)
    return FALSE;

  g_ptr_array_sort (caps->structs, gst_caps_compare_structures);

  start = caps->structs->len - 1;
  for (i = caps->structs->len - 1; i >= 0; i--) {
    simplify = gst_caps_get_structure (caps, i);
    if (gst_structure_get_name_id (simplify) !=
        gst_structure_get_name_id (gst_caps_get_structure (caps, start)))
      start = i;
    for (j = start; j >= 0; j--) {
      if (j == i)
        continue;
      compare = gst_caps_get_structure (caps, j);
      if (gst_structure_get_name_id (simplify) !=
          gst_structure_get_name_id (compare)) {
        break;
      }
      if (gst_caps_structure_simplify (&result, simplify, compare)) {
#if 0
        g_print ("%s  -  %s  =  %s\n",
            gst_structure_to_string (simplify),
            gst_structure_to_string (compare),
            result ? gst_structure_to_string (result) : "---");
#endif
        if (result) {
          gst_structure_free (simplify);
          g_ptr_array_index (caps->structs, i) = result;
          simplify = result;
        } else {
          gst_caps_remove_structure (caps, i);
          start--;
          break;
        }
        changed = TRUE;
      }
    }
  }

  if (!changed)
    return FALSE;

  /* gst_caps_do_simplify (caps); */
  return TRUE;
}

#ifndef GST_DISABLE_LOADSAVE
/**
 * gst_caps_save_thyself:
 * @caps: a #GstCaps structure
 * @parent: a XML parent node
 *
 * Serializes a #GstCaps to XML and adds it as a child node of @parent.
 *
 * Returns: a XML node pointer
 */
xmlNodePtr
gst_caps_save_thyself (const GstCaps * caps, xmlNodePtr parent)
{
  char *s = gst_caps_to_string (caps);

  xmlNewChild (parent, NULL, "caps", s);
  g_free (s);
  return parent;
}

/**
 * gst_caps_load_thyself:
 * @parent: a XML node
 *
 * Creates a #GstCaps from its XML serialization.
 *
 * Returns: a new #GstCaps structure
 */
GstCaps *
gst_caps_load_thyself (xmlNodePtr parent)
{
  if (strcmp ("caps", parent->name) == 0) {
    return gst_caps_from_string (xmlNodeGetContent (parent));
  }

  return NULL;
}
#endif

/* utility */

/**
 * gst_caps_replace:
 * @caps: a pointer to #GstCaps
 * @newcaps: a #GstCaps to replace *caps
 *
 * Replaces *caps with @newcaps.  Frees the #GstCaps in the location
 * pointed to by @caps, if applicable, then modifies @caps to point to
 * @newcaps.
 */
void
gst_caps_replace (GstCaps ** caps, GstCaps * newcaps)
{
#if 0                           /* disable this, since too many plugins rely on undefined behavior */
#ifdef USE_POISONING
  //if (newcaps) CAPS_POISON (newcaps);
#endif
#endif
  if (*caps)
    gst_caps_free (*caps);
  *caps = newcaps;
}

/**
 * gst_caps_to_string:
 * @caps: a #GstCaps
 *
 * Converts @caps to a string representation.  This string representation
 * can be converted back to a #GstCaps by #gst_caps_from_string.
 *
 * Returns: a newly allocated string representing @caps.
 */
gchar *
gst_caps_to_string (const GstCaps * caps)
{
  int i;
  GstStructure *structure;
  GString *s;
  char *sstr;

  /* NOTE:  This function is potentially called by the debug system,
   * so any calls to gst_log() (and GST_DEBUG(), GST_LOG(), etc.)
   * should be careful to avoid recursion.  This includes any functions
   * called by gst_caps_to_string.  In particular, calls should
   * not use the GST_PTR_FORMAT extension.  */

  /* FIXME does this leak? */

  if (caps == NULL) {
    return g_strdup ("NULL");
  }
  if (gst_caps_is_any (caps)) {
    return g_strdup ("ANY");
  }
  if (gst_caps_is_empty (caps)) {
    return g_strdup ("EMPTY");
  }
  s = g_string_new ("");
  structure = gst_caps_get_structure (caps, 0);
  sstr = gst_structure_to_string (structure);
  g_string_append (s, sstr);
  g_free (sstr);

  for (i = 1; i < caps->structs->len; i++) {
    structure = gst_caps_get_structure (caps, i);

    g_string_append (s, "; ");
    sstr = gst_structure_to_string (structure);
    g_string_append (s, sstr);
    g_free (sstr);
  }

  return g_string_free (s, FALSE);
}

static gboolean
gst_caps_from_string_inplace (GstCaps * caps, const gchar * string)
{
  GstStructure *structure;
  gchar *s;

  g_return_val_if_fail (string, FALSE);
  if (strcmp ("ANY", string) == 0) {
    caps->flags = GST_CAPS_FLAGS_ANY;
    return TRUE;
  }
  if (strcmp ("EMPTY", string) == 0) {
    return TRUE;
  }

  structure = gst_structure_from_string (string, &s);
  if (structure == NULL) {
    return FALSE;
  }
  gst_caps_append_structure (caps, structure);

  while (*s == ';') {
    s++;
    while (g_ascii_isspace (*s))
      s++;
    structure = gst_structure_from_string (s, &s);
    if (structure == NULL) {
      return FALSE;
    }
    gst_caps_append_structure (caps, structure);
    while (g_ascii_isspace (*s))
      s++;
  }

  if (*s != 0) {
    return FALSE;
  }

  return TRUE;
}

/**
 * gst_caps_from_string:
 * @string: a string to convert to #GstCaps
 *
 * Converts @caps from a string representation.
 *
 * Returns: a newly allocated #GstCaps
 */
GstCaps *
gst_caps_from_string (const gchar * string)
{
  GstCaps *caps;

  caps = gst_caps_new_empty ();
  if (gst_caps_from_string_inplace (caps, string)) {
    return caps;
  } else {
    gst_caps_free (caps);
    return NULL;
  }
}

static void
gst_caps_transform_to_string (const GValue * src_value, GValue * dest_value)
{
  g_return_if_fail (G_IS_VALUE (src_value));
  g_return_if_fail (G_IS_VALUE (dest_value));
  g_return_if_fail (G_VALUE_HOLDS (src_value, GST_TYPE_CAPS));
  g_return_if_fail (G_VALUE_HOLDS (dest_value, G_TYPE_STRING)
      || G_VALUE_HOLDS (dest_value, G_TYPE_POINTER));

  dest_value->data[0].v_pointer =
      gst_caps_to_string (src_value->data[0].v_pointer);
}

static GstCaps *
gst_caps_copy_conditional (const GstCaps * src)
{
  if (src) {
    return gst_caps_copy (src);
  } else {
    return NULL;
  }
}

/* fixate utility functions */

/**
 * gst_caps_structure_fixate_field_nearest_int:
 * @structure: a #GstStructure
 * @field_name: a field in @structure
 * @target: the target value of the fixation
 *
 * Fixates a #GstStructure by changing the given field to the nearest
 * integer to @target that is a subset of the existing field.
 *
 * Returns: TRUE if the structure could be fixated
 */
gboolean
gst_caps_structure_fixate_field_nearest_int (GstStructure * structure,
    const char *field_name, int target)
{
  const GValue *value;

  g_return_val_if_fail (gst_structure_has_field (structure, field_name), FALSE);

  value = gst_structure_get_value (structure, field_name);

  if (G_VALUE_TYPE (value) == G_TYPE_INT) {
    /* already fixed */
    return FALSE;
  } else if (G_VALUE_TYPE (value) == GST_TYPE_INT_RANGE) {
    int x;

    x = gst_value_get_int_range_min (value);
    if (target < x)
      target = x;
    x = gst_value_get_int_range_max (value);
    if (target > x)
      target = x;
    gst_structure_set (structure, field_name, G_TYPE_INT, target, NULL);
    return TRUE;
  } else if (G_VALUE_TYPE (value) == GST_TYPE_LIST) {
    const GValue *list_value;
    int i, n;
    int best = 0;
    int best_index = -1;

    n = gst_value_list_get_size (value);
    for (i = 0; i < n; i++) {
      list_value = gst_value_list_get_value (value, i);
      if (G_VALUE_TYPE (list_value) == G_TYPE_INT) {
        int x = g_value_get_int (list_value);

        if (best_index == -1 || (ABS (target - x) < ABS (target - best))) {
          best_index = i;
          best = x;
        }
      }
    }
    if (best_index != -1) {
      gst_structure_set (structure, field_name, G_TYPE_INT, best, NULL);
      return TRUE;
    }
    return FALSE;
  }

  return FALSE;
}

/**
 * gst_caps_structure_fixate_field_nearest_double:
 * @structure: a #GstStructure
 * @field_name: a field in @structure
 * @target: the target value of the fixation
 *
 * Fixates a #GstStructure by changing the given field to the nearest
 * double to @target that is a subset of the existing field.
 *
 * Returns: TRUE if the structure could be fixated
 */
gboolean
gst_caps_structure_fixate_field_nearest_double (GstStructure * structure,
    const char *field_name, double target)
{
  const GValue *value;

  g_return_val_if_fail (gst_structure_has_field (structure, field_name), FALSE);

  value = gst_structure_get_value (structure, field_name);

  if (G_VALUE_TYPE (value) == G_TYPE_DOUBLE) {
    /* already fixed */
    return FALSE;
  } else if (G_VALUE_TYPE (value) == GST_TYPE_DOUBLE_RANGE) {
    double x;

    x = gst_value_get_double_range_min (value);
    if (target < x)
      target = x;
    x = gst_value_get_double_range_max (value);
    if (target > x)
      target = x;
    gst_structure_set (structure, field_name, G_TYPE_DOUBLE, target, NULL);
    return TRUE;
  } else if (G_VALUE_TYPE (value) == GST_TYPE_LIST) {
    const GValue *list_value;
    int i, n;
    double best = 0;
    int best_index = -1;

    n = gst_value_list_get_size (value);
    for (i = 0; i < n; i++) {
      list_value = gst_value_list_get_value (value, i);
      if (G_VALUE_TYPE (list_value) == G_TYPE_DOUBLE) {
        double x = g_value_get_double (list_value);

        if (best_index == -1 || (ABS (target - x) < ABS (target - best))) {
          best_index = i;
          best = x;
        }
      }
    }
    if (best_index != -1) {
      gst_structure_set (structure, field_name, G_TYPE_DOUBLE, best, NULL);
      return TRUE;
    }
    return FALSE;
  }

  return FALSE;

}


const GstStructure *
gst_caps_get_preferred (const GstCaps * caps)
{
  g_return_val_if_fail (GST_IS_CAPS (caps), NULL);

  return caps->preferred;
}

void
gst_caps_set_preferred (GstCaps * caps, const GstStructure * structure)
{
  g_return_if_fail (GST_IS_CAPS (caps));
  g_return_if_fail (GST_IS_STRUCTURE (structure));

  if (caps->preferred)
    gst_structure_free (caps->preferred);
  caps->preferred = gst_structure_copy (structure);
}

GstStructure *
gst_caps_get_structure_by_id (const GstCaps * caps, GQuark id)
{
  int i;
  GstStructure *structure;

  g_return_val_if_fail (GST_IS_CAPS (caps), NULL);

  for (i = 0; i < gst_caps_get_size (caps); i++) {
    structure = gst_caps_get_structure (caps, i);
    if (structure->name == id) {
      return structure;
    }
  }

  return NULL;
}

static gboolean
gst_caps_prefer_foreach (GQuark name, GValue * value, gpointer user_data)
{
  GstStructure *structure = (GstStructure *) user_data;
  const GValue *svalue;
  GValue ivalue = { 0 };
  gboolean ret;

  svalue = gst_structure_id_get_value (structure, name);
  if (svalue == NULL)
    return TRUE;

  if (G_VALUE_TYPE (value) == G_TYPE_INT) {
    int target = g_value_get_int (value);

    gst_caps_structure_fixate_field_nearest_int (structure,
        g_quark_to_string (name), target);
  } else if (G_VALUE_TYPE (value) == G_TYPE_DOUBLE) {
    double target = g_value_get_double (value);

    gst_caps_structure_fixate_field_nearest_double (structure,
        g_quark_to_string (name), target);
  } else {
    ret = gst_value_intersect (&ivalue, value, svalue);
    if (ret) {
      gst_structure_id_set_value (structure, name, &ivalue);
      g_value_unset (&ivalue);
    }
  }
  return TRUE;
}

GstCaps *
gst_caps_use_preferred (const GstCaps * caps)
{
  GstCaps *pcaps;
  GstStructure *structure;

  g_return_val_if_fail (GST_IS_CAPS (caps), NULL);

  if (!caps->preferred || gst_caps_is_any (caps) || gst_caps_is_empty (caps)
      || gst_caps_is_fixed (caps)) {
    return gst_caps_copy (caps);
  }

  if (gst_caps_is_simple (caps)) {
    structure = gst_caps_get_structure (caps, 0);
  } else {
    structure = gst_caps_get_structure_by_id (caps, caps->preferred->name);
  }

  if (structure) {
    structure = gst_structure_copy (structure);

    gst_structure_foreach (caps->preferred, gst_caps_prefer_foreach, structure);

    pcaps = gst_caps_new_full (structure, NULL);

    return pcaps;
  }

  /* FIXME */

  return NULL;
}