## GstValue GstValue — GValue and GParamSpec implementations specific to GStreamer |

## Synopsis

    #include <gst/gst.h>

    #define             GST_VALUE_HOLDS_FOURCC              (x)
    #define             GST_MAKE_FOURCC                     (a,b,c,d)
    #define             GST_STR_FOURCC                      (f)
    #define             GST_FOURCC_FORMAT
    #define             GST_FOURCC_ARGS                     (fourcc)
    #define             GST_TYPE_FOURCC
    void                gst_value_set_fourcc                (GValue *value,
                                                             guint32 fourcc);
    guint32             gst_value_get_fourcc                (const GValue *value);

    #define             GST_VALUE_HOLDS_INT_RANGE           (x)
    #define             GST_TYPE_INT_RANGE
    void                gst_value_set_int_range             (GValue *value,
                                                             gint start,
                                                             gint end);
    gint                gst_value_get_int_range_min         (const GValue *value);
    gint                gst_value_get_int_range_max         (const GValue *value);

    #define             GST_VALUE_HOLDS_DOUBLE_RANGE        (x)
    #define             GST_TYPE_DOUBLE_RANGE
    void                gst_value_set_double_range          (GValue *value,
                                                             gdouble start,
                                                             gdouble end);
    gdouble             gst_value_get_double_range_min      (const GValue *value);
    gdouble             gst_value_get_double_range_max      (const GValue *value);

    #define             GST_VALUE_HOLDS_LIST                (x)
    #define             GST_TYPE_LIST
    #define             GST_VALUE_HOLDS_ARRAY               (x)
    #define             GST_TYPE_ARRAY
    void                gst_value_list_append_value         (GValue *value,
                                                             const GValue *append_value);
    void                gst_value_list_prepend_value        (GValue *value,
                                                             const GValue *prepend_value);
    void                gst_value_list_concat               (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);
    guint               gst_value_list_get_size             (const GValue *value);
    const GValue*       gst_value_list_get_value            (const GValue *value,
                                                             guint index);

    #define             GST_VALUE_HOLDS_FRACTION            (x)
    #define             GST_TYPE_FRACTION
    void                gst_value_set_fraction              (GValue *value,
                                                             gint numerator,
                                                             gint denominator);
    gint                gst_value_get_fraction_numerator    (const GValue *value);
    gint                gst_value_get_fraction_denominator  (const GValue *value);
    gboolean            gst_value_fraction_multiply         (GValue *product,
                                                             const GValue *factor1,
                                                             const GValue *factor2);
    gboolean            gst_value_fraction_subtract         (GValue *dest,
                                                             const GValue *minuend,
                                                             const GValue *subtrahend);

                        GstParamSpecFraction;
    GParamSpec*         gst_param_spec_fraction             (const gchar *name,
                                                             const gchar *nick,
                                                             const gchar *blurb,
                                                             gint min_num,
                                                             gint min_denom,
                                                             gint max_num,
                                                             gint max_denom,
                                                             gint default_num,
                                                             gint default_denom,
                                                             GParamFlags flags);

    #define             GST_VALUE_HOLDS_FRACTION_RANGE      (x)
    #define             GST_TYPE_FRACTION_RANGE
    void                gst_value_set_fraction_range        (GValue *value,
                                                             const GValue *start,
                                                             const GValue *end);
    const GValue*       gst_value_get_fraction_range_min    (const GValue *value);
    const GValue*       gst_value_get_fraction_range_max    (const GValue *value);
    void                gst_value_set_fraction_range_full   (GValue *value,
                                                             gint numerator_start,
                                                             gint denominator_start,
                                                             gint numerator_end,
                                                             gint denominator_end);

    #define             GST_VALUE_HOLDS_DATE                (x)
    #define             GST_TYPE_DATE
    void                gst_value_set_date                  (GValue *value,
                                                             const GDate *date);
    const GDate*        gst_value_get_date                  (const GValue *value);

    #define             GST_VALUE_HOLDS_CAPS                (x)
    void                gst_value_set_caps                  (GValue *value,
                                                             const GstCaps *caps);
    const GstCaps*      gst_value_get_caps                  (const GValue *value);

    #define             GST_VALUE_HOLDS_STRUCTURE           (x)
    void                gst_value_set_structure             (GValue *value,
                                                             const GstStructure *structure);
    const GstStructure* gst_value_get_structure             (const GValue *value);

    #define             GST_VALUE_HOLDS_MINI_OBJECT         (value)
    #define             GST_VALUE_HOLDS_BUFFER              (x)
    #define             gst_value_get_buffer                (v)
    #define             gst_value_set_buffer                (v,b)
    #define             gst_value_take_buffer               (v,b)

    #define             GST_VALUE_LESS_THAN
    #define             GST_VALUE_EQUAL
    #define             GST_VALUE_GREATER_THAN
    #define             GST_VALUE_UNORDERED
    gint                (*GstValueCompareFunc)              (const GValue *value1,
                                                             const GValue *value2);
    gchar*              (*GstValueSerializeFunc)            (const GValue *value1);
    gboolean            (*GstValueDeserializeFunc)          (GValue *dest,
                                                             const gchar *s);
    gboolean            (*GstValueUnionFunc)                (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);
    gboolean            (*GstValueIntersectFunc)            (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);
    gboolean            (*GstValueSubtractFunc)             (GValue *dest,
                                                             const GValue *minuend,
                                                             const GValue *subtrahend);
                        GstValueTable;
    gboolean            gst_value_is_fixed                  (const GValue *value);
    void                gst_value_register                  (const GstValueTable *table);
    void                gst_value_init_and_copy             (GValue *dest,
                                                             const GValue *src);
    gchar*              gst_value_serialize                 (const GValue *value);
    gboolean            gst_value_deserialize               (GValue *dest,
                                                             const gchar *src);
    gint                gst_value_compare                   (const GValue *value1,
                                                             const GValue *value2);
    gboolean            gst_value_can_compare               (const GValue *value1,
                                                             const GValue *value2);
    gboolean            gst_value_union                     (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);
    gboolean            gst_value_can_union                 (const GValue *value1,
                                                             const GValue *value2);
    void                gst_value_register_union_func       (GType type1,
                                                             GType type2,
                                                             GstValueUnionFunc func);
    gboolean            gst_value_subtract                  (GValue *dest,
                                                             const GValue *minuend,
                                                             const GValue *subtrahend);
    gboolean            gst_value_can_subtract              (const GValue *minuend,
                                                             const GValue *subtrahend);
    void                gst_value_register_subtract_func    (GType minuend_type,
                                                             GType subtrahend_type,
                                                             GstValueSubtractFunc func);
    gboolean            gst_value_intersect                 (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);
    gboolean            gst_value_can_intersect             (const GValue *value1,
                                                             const GValue *value2);
    void                gst_value_register_intersect_func   (GType type1,
                                                             GType type2,
                                                             GstValueIntersectFunc func);
    void                gst_value_array_append_value        (GValue *value,
                                                             const GValue *append_value);
    guint               gst_value_array_get_size            (const GValue *value);
    const GValue*       gst_value_array_get_value           (const GValue *value,
                                                             guint index);
    void                gst_value_array_prepend_value       (GValue *value,
                                                             const GValue *prepend_value);

## Description

GValue and GParamSpec implementations specific to GStreamer.

Note that operations on the same GstValue (or GValue) from multiple threads may lead to undefined behaviour.

Last reviewed on 2006-03-07 (0.10.4)

## Details

### GST_VALUE_HOLDS_FOURCC()

    #define GST_VALUE_HOLDS_FOURCC(x)       (G_VALUE_HOLDS(x, gst_fourcc_get_type ()))

Checks if the given GValue contains a GST_TYPE_FOURCC value.

`x` : | the GValue to check

### GST_MAKE_FOURCC()

    #define GST_MAKE_FOURCC(a,b,c,d)        (guint32)((a)|(b)<<8|(c)<<16|(d)<<24)

Transform four characters into a guint32 fourcc value with host endianness.

    guint32 fourcc = GST_MAKE_FOURCC ('M', 'J', 'P', 'G');

`a` : | the first character
`b` : | the second character
`c` : | the third character
`d` : | the fourth character

### GST_STR_FOURCC()

    #define GST_STR_FOURCC(f)               (guint32)(((f)[0])|((f)[1]<<8)|((f)[2]<<16)|((f)[3]<<24))

Transform an input string into a guint32 fourcc value with host endianness. Caller is responsible for ensuring the input string consists of at least four characters.

    guint32 fourcc = GST_STR_FOURCC ("MJPG");

`f` : | a string with at least four characters

### GST_FOURCC_FORMAT

    #define GST_FOURCC_FORMAT "c%c%c%c"

Can be used together with GST_FOURCC_ARGS to properly output a guint32 fourcc value in a `printf()`-style text message.

    printf ("fourcc: %" GST_FOURCC_FORMAT "\n", GST_FOURCC_ARGS (fcc));

### GST_FOURCC_ARGS()

    #define             GST_FOURCC_ARGS(fourcc)

Can be used together with GST_FOURCC_FORMAT to properly output a guint32 fourcc value in a `printf()`-style text message.

`fourcc` : | a guint32 fourcc value to output

### GST_TYPE_FOURCC

    #define GST_TYPE_FOURCC                  gst_fourcc_get_type ()

a GValue type that represents 4 byte identifier (e.g. used for codecs)

### gst_value_set_fourcc ()

    void                gst_value_set_fourcc                (GValue *value,
                                                             guint32 fourcc);

Sets `value` to `fourcc`.

`value` : | a GValue initialized to GST_TYPE_FOURCC
`fourcc` : | the guint32 fourcc to set

### gst_value_get_fourcc ()

    guint32             gst_value_get_fourcc                (const GValue *value);

Gets the guint32 fourcc contained in `value`.

`value` : | a GValue initialized to GST_TYPE_FOURCC
Returns : | the guint32 fourcc contained in `value`.

### GST_VALUE_HOLDS_INT_RANGE()

    #define GST_VALUE_HOLDS_INT_RANGE(x)    (G_VALUE_HOLDS(x, gst_int_range_get_type ()))

Checks if the given GValue contains a GST_TYPE_INT_RANGE value.

`x` : | the GValue to check

### GST_TYPE_INT_RANGE

    #define GST_TYPE_INT_RANGE               gst_int_range_get_type ()

a GValue type that represents an integer range

### gst_value_set_int_range ()

    void                gst_value_set_int_range             (GValue *value,
                                                             gint start,
                                                             gint end);

Sets `value` to the range specified by `start` and `end`.

`value` : | a GValue initialized to GST_TYPE_INT_RANGE
`start` : | the start of the range
`end` : | the end of the range

### gst_value_get_int_range_min ()

    gint                gst_value_get_int_range_min         (const GValue *value);

Gets the minimum of the range specified by `value`.

`value` : | a GValue initialized to GST_TYPE_INT_RANGE
Returns : | the minimum of the range

### gst_value_get_int_range_max ()

    gint                gst_value_get_int_range_max         (const GValue *value);

Gets the maximum of the range specified by `value`.

`value` : | a GValue initialized to GST_TYPE_INT_RANGE
Returns : | the maxumum of the range

### GST_VALUE_HOLDS_DOUBLE_RANGE()

    #define GST_VALUE_HOLDS_DOUBLE_RANGE(x) (G_VALUE_HOLDS(x, gst_double_range_get_type ()))

Checks if the given GValue contains a GST_TYPE_DOUBLE_RANGE value.

`x` : | the GValue to check

### GST_TYPE_DOUBLE_RANGE

    #define GST_TYPE_DOUBLE_RANGE            gst_double_range_get_type ()

a GValue type that represents a floating point range with double precission

### gst_value_set_double_range ()

    void                gst_value_set_double_range          (GValue *value,
                                                             gdouble start,
                                                             gdouble end);

Sets `value` to the range specified by `start` and `end`.

`value` : | a GValue initialized to GST_TYPE_DOUBLE_RANGE
`start` : | the start of the range
`end` : | the end of the range

### gst_value_get_double_range_min ()

    gdouble             gst_value_get_double_range_min      (const GValue *value);

Gets the minimum of the range specified by `value`.

`value` : | a GValue initialized to GST_TYPE_DOUBLE_RANGE
Returns : | the minumum of the range

### gst_value_get_double_range_max ()

    gdouble             gst_value_get_double_range_max      (const GValue *value);

Gets the maximum of the range specified by `value`.

`value` : | a GValue initialized to GST_TYPE_DOUBLE_RANGE
Returns : | the maxumum of the range

### GST_VALUE_HOLDS_LIST()

    #define GST_VALUE_HOLDS_LIST(x)		(G_VALUE_HOLDS(x, gst_value_list_get_type ()))

Checks if the given GValue contains a GST_TYPE_LIST value.

`x` : | the GValue to check

### GST_TYPE_LIST

    #define GST_TYPE_LIST                    gst_value_list_get_type ()

a GValue type that represents an unordered list of GValue values. This is used for example to express a list of possible values for a field in a caps structure, like a list of possible sample rates, of which only one will be chosen in the end. This means that all values in the list are meaningful on their own.

### GST_VALUE_HOLDS_ARRAY()

    #define GST_VALUE_HOLDS_ARRAY(x)	(G_VALUE_HOLDS(x, gst_value_array_get_type ()))

Checks if the given GValue contains a GST_TYPE_ARRAY value.

`x` : | the GValue to check

### GST_TYPE_ARRAY

    #define GST_TYPE_ARRAY			 gst_value_array_get_type ()

a GValue type that represents an ordered list of GValue values. This is used to express a set of values that is meaningful only in their specific combination and order of values. Each value on its own is not particularly meaningful, only the ordered array in its entirety is meaningful. This is used for example to express channel layouts for multichannel audio where each channel needs to be mapped to a position in the room.

### gst_value_list_append_value ()

    void                gst_value_list_append_value         (GValue *value,
                                                             const GValue *append_value);

Appends `append_value` to the GstValueList in `value`.

`value` : | a GValue of type GST_TYPE_LIST
`append_value` : | the value to append

### gst_value_list_prepend_value ()

    void                gst_value_list_prepend_value        (GValue *value,
                                                             const GValue *prepend_value);

Prepends `prepend_value` to the GstValueList in `value`.

`value` : | a GValue of type GST_TYPE_LIST
`prepend_value` : | the value to prepend

### gst_value_list_concat ()

    void                gst_value_list_concat               (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);

Concatenates copies of `value1` and `value2` into a list. Values that are not of type GST_TYPE_LIST are treated as if they were lists of length 1. `dest` will be initialized to the type GST_TYPE_LIST.

`dest` : | an uninitialized GValue to take the result
`value1` : | a GValue
`value2` : | a GValue

### gst_value_list_get_size ()

    guint               gst_value_list_get_size             (const GValue *value);

Gets the number of values contained in `value`.

`value` : | a GValue of type GST_TYPE_LIST
Returns : | the number of values

### gst_value_list_get_value ()

    const GValue*       gst_value_list_get_value            (const GValue *value,
                                                             guint index);

Gets the value that is a member of the list contained in `value` and has the index `index`.

`value` : | a GValue of type GST_TYPE_LIST
`index` : | index of value to get from the list
Returns : | the value at the given index

### GST_VALUE_HOLDS_FRACTION()

    #define GST_VALUE_HOLDS_FRACTION(x)	(G_VALUE_HOLDS(x, gst_fraction_get_type ()))

Checks if the given GValue contains a GST_TYPE_FRACTION value.

`x` : | the GValue to check

### GST_TYPE_FRACTION

    #define GST_TYPE_FRACTION                gst_fraction_get_type ()

a GValue type that represents a fraction of an integer numerator over an integer denominator

### gst_value_set_fraction ()

    void                gst_value_set_fraction              (GValue *value,
                                                             gint numerator,
                                                             gint denominator);

Sets `value` to the fraction specified by `numerator` over `denominator`. The fraction gets reduced to the smallest numerator and denominator, and if necessary the sign is moved to the numerator.

`value` : | a GValue initialized to GST_TYPE_FRACTION
`numerator` : | the numerator of the fraction
`denominator` : | the denominator of the fraction

### gst_value_get_fraction_numerator ()

    gint                gst_value_get_fraction_numerator    (const GValue *value);

Gets the numerator of the fraction specified by `value`.

`value` : | a GValue initialized to GST_TYPE_FRACTION
Returns : | the numerator of the fraction.

### gst_value_get_fraction_denominator ()

    gint                gst_value_get_fraction_denominator  (const GValue *value);

Gets the denominator of the fraction specified by `value`.

`value` : | a GValue initialized to GST_TYPE_FRACTION
Returns : | the denominator of the fraction.

### gst_value_fraction_multiply ()

    gboolean            gst_value_fraction_multiply         (GValue *product,
                                                             const GValue *factor1,
                                                             const GValue *factor2);

Multiplies the two GValues containing a GstFraction and sets `product` to the product of the two fractions.

`product` : | a GValue initialized to GST_TYPE_FRACTION
`factor1` : | a GValue initialized to GST_TYPE_FRACTION
`factor2` : | a GValue initialized to GST_TYPE_FRACTION
Returns : | FALSE in case of an error (like integer overflow), TRUE otherwise.

### gst_value_fraction_subtract ()

    gboolean            gst_value_fraction_subtract         (GValue *dest,
                                                             const GValue *minuend,
                                                             const GValue *subtrahend);

Subtracts the `subtrahend` from the `minuend` and sets `dest` to the result.

`dest` : | a GValue initialized to GST_TYPE_FRACTION
`minuend` : | a GValue initialized to GST_TYPE_FRACTION
`subtrahend` : | a GValue initialized to GST_TYPE_FRACTION
Returns : | FALSE in case of an error (like integer overflow), TRUE otherwise.

### GstParamSpecFraction

    typedef struct {
      GParamSpec    parent_instance;

      gint          min_num, min_den;
      gint          max_num, max_den;
      gint          def_num, def_den;
    } GstParamSpecFraction;

A GParamSpec derived structure that contains the meta data for fractional properties.

GParamSpec `parent_instance`; | super class
gint `min_num`; | minimal numerator
gint `min_den`; | minimal denominator
gint `max_num`; | maximal numerator
gint `max_den`; | maximal denominator
gint `def_num`; | default numerator
gint `def_den`; | default denominator

### gst_param_spec_fraction ()

    GParamSpec*         gst_param_spec_fraction             (const gchar *name,
                                                             const gchar *nick,
                                                             const gchar *blurb,
                                                             gint min_num,
                                                             gint min_denom,
                                                             gint max_num,
                                                             gint max_denom,
                                                             gint default_num,
                                                             gint default_denom,
                                                             GParamFlags flags);

This function creates a fraction GParamSpec for use by objects/elements that want to expose properties of fraction type. This function is typically used in connection with `g_object_class_install_property()` in a GObjects's instance_init function.

`name` : | canonical name of the property specified
`nick` : | nick name for the property specified
`blurb` : | description of the property specified
`min_num` : | minimum value (fraction numerator)
`min_denom` : | minimum value (fraction denominator)
`max_num` : | maximum value (fraction numerator)
`max_denom` : | maximum value (fraction denominator)
`default_num` : | default value (fraction numerator)
`default_denom` : | default value (fraction denominator)
`flags` : | flags for the property specified
Returns : | a newly created parameter specification

Since 0.10.14

### GST_VALUE_HOLDS_FRACTION_RANGE()

    #define GST_VALUE_HOLDS_FRACTION_RANGE(x)    (G_VALUE_HOLDS(x, gst_fraction_range_get_type ()))

Checks if the given GValue contains a GST_TYPE_FRACTION_RANGE value.

`x` : | the GValue to check

### GST_TYPE_FRACTION_RANGE

    #define GST_TYPE_FRACTION_RANGE            gst_fraction_range_get_type ()

a GValue type that represents a GstFraction range

### gst_value_set_fraction_range ()

    void                gst_value_set_fraction_range        (GValue *value,
                                                             const GValue *start,
                                                             const GValue *end);

Sets `value` to the range specified by `start` and `end`.

`value` : | a GValue initialized to GST_TYPE_FRACTION_RANGE
`start` : | the start of the range (a GST_TYPE_FRACTION GValue)
`end` : | the end of the range (a GST_TYPE_FRACTION GValue)

### gst_value_get_fraction_range_min ()

    const GValue*       gst_value_get_fraction_range_min    (const GValue *value);

Gets the minimum of the range specified by `value`.

`value` : | a GValue initialized to GST_TYPE_FRACTION_RANGE
Returns : | the minumum of the range

### gst_value_get_fraction_range_max ()

    const GValue*       gst_value_get_fraction_range_max    (const GValue *value);

Gets the maximum of the range specified by `value`.

`value` : | a GValue initialized to GST_TYPE_FRACTION_RANGE
Returns : | the maximum of the range

### gst_value_set_fraction_range_full ()

    void                gst_value_set_fraction_range_full   (GValue *value,
                                                             gint numerator_start,
                                                             gint denominator_start,
                                                             gint numerator_end,
                                                             gint denominator_end);

Sets `value` to the range specified by `numerator_start`/`denominator_start` and `numerator_end`/`denominator_end`.

`value` : | a GValue initialized to GST_TYPE_FRACTION_RANGE
`numerator_start` : | the numerator start of the range
`denominator_start` : | the denominator start of the range
`numerator_end` : | the numerator end of the range
`denominator_end` : | the denominator end of the range

### GST_VALUE_HOLDS_DATE()

    #define GST_VALUE_HOLDS_DATE(x)         (G_VALUE_HOLDS(x, gst_date_get_type ()))

Checks if the given GValue contains a GST_TYPE_DATE value.

`x` : | the GValue to check

### GST_TYPE_DATE

    #define GST_TYPE_DATE                    gst_date_get_type ()

a boxed GValue type for GDate that represents a date.

### gst_value_set_date ()

    void                gst_value_set_date                  (GValue *value,
                                                             const GDate *date);

Sets the contents of `value` to coorespond to `date`. The actual GDate structure is copied before it is used.

`value` : | a GValue initialized to GST_TYPE_DATE
`date` : | the date to set the value to

### gst_value_get_date ()

    const GDate*        gst_value_get_date                  (const GValue *value);

Gets the contents of `value`.

`value` : | a GValue initialized to GST_TYPE_DATE
Returns : | the contents of `value`

### GST_VALUE_HOLDS_CAPS()

    #define GST_VALUE_HOLDS_CAPS(x)		(G_VALUE_HOLDS(x, GST_TYPE_CAPS))

Checks if the given GValue contains a GST_TYPE_CAPS value.

`x` : | the GValue to check

### gst_value_set_caps ()

    void                gst_value_set_caps                  (GValue *value,
                                                             const GstCaps *caps);

Sets the contents of `value` to `caps`. The actual GstCaps structure is copied before it is used.

`value` : | a GValue initialized to GST_TYPE_CAPS
`caps` : | the caps to set the value to

### gst_value_get_caps ()

    const GstCaps*      gst_value_get_caps                  (const GValue *value);

Gets the contents of `value`.

`value` : | a GValue initialized to GST_TYPE_CAPS
Returns : | the contents of `value`

### GST_VALUE_HOLDS_STRUCTURE()

    #define GST_VALUE_HOLDS_STRUCTURE(x)		(G_VALUE_HOLDS(x, GST_TYPE_STRUCTURE))

Checks if the given GValue contains a GST_TYPE_STRUCTURE value.

`x` : | the GValue to check

Since 0.10.15

### gst_value_set_structure ()

    void                gst_value_set_structure             (GValue *value,
                                                             const GstStructure *structure);

Sets the contents of `value` to `structure`. The actual

`value` : | a GValue initialized to GST_TYPE_STRUCTURE
`structure` : | the structure to set the value to

Since 0.10.15

### gst_value_get_structure ()

    const GstStructure* gst_value_get_structure             (const GValue *value);

Gets the contents of `value`.

`value` : | a GValue initialized to GST_TYPE_STRUCTURE
Returns : | the contents of `value`

Since 0.10.15

### GST_VALUE_HOLDS_MINI_OBJECT()

    #define GST_VALUE_HOLDS_MINI_OBJECT(value)  (G_VALUE_HOLDS(value, GST_TYPE_MINI_OBJECT))

Checks if the given GValue contains a GST_TYPE_MINI_OBJECT value.

`value` : | the GValue to check

### GST_VALUE_HOLDS_BUFFER()

    #define GST_VALUE_HOLDS_BUFFER(x)       (G_VALUE_HOLDS(x, GST_TYPE_BUFFER))

Checks if the given GValue contains a GST_TYPE_BUFFER value.

`x` : | the GValue to check

### gst_value_get_buffer()

    #define		gst_value_get_buffer(v)		GST_BUFFER_CAST (gst_value_get_mini_object(v))

Receives a GstBuffer as the value of `v`. Does not return a reference to the buffer, so the pointer is only valid for as long as the caller owns a reference to `v`.

`v` : | a GstValue to qeury

### gst_value_set_buffer()

    #define		gst_value_set_buffer(v,b)	gst_value_set_mini_object(v, GST_MINI_OBJECT_CAST(b))

Sets `b` as the value of `v`. Caller retains reference to buffer.

`v` : | a GstValue to receive the data
`b` : | a GstBuffer to assign to the GstValue

### gst_value_take_buffer()

    #define		gst_value_take_buffer(v,b)	gst_value_take_mini_object(v, GST_MINI_OBJECT_CAST(b))

Sets `b` as the value of `v`. Caller gives away reference to buffer.

`v` : | a GstValue to receive the data
`b` : | a GstBuffer to assign to the GstValue

### GST_VALUE_LESS_THAN

    #define GST_VALUE_LESS_THAN              (-1)

Indicates that the first value provided to a comparison function (`gst_value_compare()`) is lesser than the second one.

### GST_VALUE_EQUAL

    #define GST_VALUE_EQUAL                   0

Indicates that the first value provided to a comparison function (`gst_value_compare()`) is equal to the second one.

### GST_VALUE_GREATER_THAN

    #define GST_VALUE_GREATER_THAN            1

Indicates that the first value provided to a comparison function (`gst_value_compare()`) is greater than the second one.

### GST_VALUE_UNORDERED

    #define GST_VALUE_UNORDERED               2

Indicates that the comparison function (`gst_value_compare()`) can not determine a order for the two provided values.

### GstValueCompareFunc ()

    gint                (*GstValueCompareFunc)              (const GValue *value1,
                                                             const GValue *value2);

Used together with `gst_value_compare()` to compare GValues.

`value1` : | first value for comparission
`value2` : | second value for comparission
Returns : | one of GST_VALUE_LESS_THAN, GST_VALUE_EQUAL, GST_VALUE_GREATER_THAN or GST_VALUE_UNORDERED

### GstValueSerializeFunc ()

    gchar*              (*GstValueSerializeFunc)            (const GValue *value1);

Used by `gst_value_serialize()` to obtain a non-binary form of the GValue.

`value1` : | a GValue
Returns : | the string representation of the value

### GstValueDeserializeFunc ()

    gboolean            (*GstValueDeserializeFunc)          (GValue *dest,
                                                             const gchar *s);

Used by `gst_value_deserialize()` to parse a non-binary form into the GValue.

`dest` : | a GValue
`s` : | a string
Returns : | `TRUE` for success

### GstValueUnionFunc ()

    gboolean            (*GstValueUnionFunc)                (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);

Used by `gst_value_union()` to perform unification for a specific GValue type. Register a new implementation with `gst_value_register_union_func()`.

`dest` : | a GValue for the result
`value1` : | a GValue operand
`value2` : | a GValue operand
Returns : | `TRUE` if a union was successful

### GstValueIntersectFunc ()

    gboolean            (*GstValueIntersectFunc)            (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);

Used by `gst_value_intersect()` to perform intersection for a specific GValue type. If the intersection is non-empty, the result is placed in `dest` and TRUE is returned. If the intersection is empty, `dest` is unmodified and FALSE is returned. Register a new implementation with `gst_value_register_intersection_func()`.

`dest` : | a GValue for the result
`value1` : | a GValue operand
`value2` : | a GValue operand
Returns : | `TRUE` if the values can intersect

### GstValueSubtractFunc ()

    gboolean            (*GstValueSubtractFunc)             (GValue *dest,
                                                             const GValue *minuend,
                                                             const GValue *subtrahend);

Used by `gst_value_subtract()` to perform subtraction for a specific GValue type. Register a new implementation with `gst_value_register_subtract_func()`.

`dest` : | a GValue for the result
`minuend` : | a GValue operand
`subtrahend` : | a GValue operand
Returns : | `TRUE` if the subtraction is not empty

### GstValueTable

    typedef struct {
      GType type;
      GstValueCompareFunc compare;
      GstValueSerializeFunc serialize;
      GstValueDeserializeFunc deserialize;
    } GstValueTable;

VTable for the GValue `type`.

GType `type`; | a GType
GstValueCompareFunc `compare`; | a GstValueCompareFunc
GstValueSerializeFunc `serialize`; | a GstValueSerializeFunc
GstValueDeserializeFunc `deserialize`; | a GstValueDeserializeFunc

### gst_value_is_fixed ()

    gboolean            gst_value_is_fixed                  (const GValue *value);

Tests if the given GValue, if available in a GstStructure (or any other container) contains a "fixed" (which means: one value) or an "unfixed" (which means: multiple possible values, such as data lists or data ranges) value.

`value` : | the GValue to check
Returns : | true if the value is "fixed".

### gst_value_register ()

    void                gst_value_register                  (const GstValueTable *table);

Registers functions to perform calculations on GValues of a given type.

`table` : | structure containing functions to register

### gst_value_init_and_copy ()

    void                gst_value_init_and_copy             (GValue *dest,
                                                             const GValue *src);

Initialises the target value to be of the same type as source and then copies the contents from source to target.

`dest` : | the target value
`src` : | the source value

### gst_value_serialize ()

    gchar*              gst_value_serialize                 (const GValue *value);

tries to transform the given `value` into a string representation that allows getting back this string later on using `gst_value_deserialize()`.

`value` : | a GValue to serialize
Returns : | the serialization for `value` or NULL if none exists

### gst_value_deserialize ()

    gboolean            gst_value_deserialize               (GValue *dest,
                                                             const gchar *src);

Tries to deserialize a string into the type specified by the given GValue. If the operation succeeds, TRUE is returned, FALSE otherwise.

`dest` : | GValue to fill with contents of deserialization
`src` : | string to deserialize
Returns : | TRUE on success

### gst_value_compare ()

    gint                gst_value_compare                   (const GValue *value1,
                                                             const GValue *value2);

Compares `value1` and `value2`. If `value1` and `value2` cannot be compared, the function returns GST_VALUE_UNORDERED. Otherwise, if `value1` is greater than `value2`, GST_VALUE_GREATER_THAN is returned. If `value1` is less than `value2`, GST_VALUE_LESS_THAN is returned. If the values are equal, GST_VALUE_EQUAL is returned.

`value1` : | a value to compare
`value2` : | another value to compare
Returns : | A GstValueCompareType value

### gst_value_can_compare ()

    gboolean            gst_value_can_compare               (const GValue *value1,
                                                             const GValue *value2);

Determines if `value1` and `value2` can be compared.

`value1` : | a value to compare
`value2` : | another value to compare
Returns : | TRUE if the values can be compared

### gst_value_union ()

    gboolean            gst_value_union                     (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);

Creates a GValue cooresponding to the union of `value1` and `value2`.

`dest` : | the destination value
`value1` : | a value to union
`value2` : | another value to union
Returns : | always returns `TRUE`

### gst_value_can_union ()

    gboolean            gst_value_can_union                 (const GValue *value1,
                                                             const GValue *value2);

Determines if `value1` and `value2` can be non-trivially unioned. Any two values can be trivially unioned by adding both of them to a GstValueList. However, certain types have the possibility to be unioned in a simpler way. For example, an integer range and an integer can be unioned if the integer is a subset of the integer range. If there is the possibility that two values can be unioned, this function returns TRUE.

`value1` : | a value to union
`value2` : | another value to union
Returns : | TRUE if there is a function allowing the two values to be unioned.

### gst_value_register_union_func ()

    void                gst_value_register_union_func       (GType type1,
                                                             GType type2,
                                                             GstValueUnionFunc func);

Registers a union function that can create a union between GValues of the type `type1` and `type2`.

Union functions should be registered at startup before any pipelines are started, as `gst_value_register_union_func()` is not thread-safe and cannot be used at the same time as `gst_value_union()` or `gst_value_can_union()`.

`type1` : | a type to union
`type2` : | another type to union
`func` : | a function that implments creating a union between the two types

### gst_value_subtract ()

    gboolean            gst_value_subtract                  (GValue *dest,
                                                             const GValue *minuend,
                                                             const GValue *subtrahend);

Subtracts `subtrahend` from `minuend` and stores the result in `dest`. Note that this means subtraction as in sets, not as in mathematics.

`dest` : | the destination value for the result if the subtraction is not empty
`minuend` : | the value to subtract from
`subtrahend` : | the value to subtract
Returns : | `TRUE` if the subtraction is not empty

### gst_value_can_subtract ()

    gboolean            gst_value_can_subtract              (const GValue *minuend,
                                                             const GValue *subtrahend);

Checks if it's possible to subtract `subtrahend` from `minuend`.

`minuend` : | the value to subtract from
`subtrahend` : | the value to subtract
Returns : | TRUE if a subtraction is possible

### gst_value_register_subtract_func ()

    void                gst_value_register_subtract_func    (GType minuend_type,
                                                             GType subtrahend_type,
                                                             GstValueSubtractFunc func);

Registers `func` as a function capable of subtracting the values of `subtrahend_type` from values of `minuend_type`.

Subtract functions should be registered at startup before any pipelines are started, as `gst_value_register_subtract_func()` is not thread-safe and cannot be used at the same time as `gst_value_subtract()`.

`minuend_type` : | type of the minuend
`subtrahend_type` : | type of the subtrahend
`func` : | function to use

### gst_value_intersect ()

    gboolean            gst_value_intersect                 (GValue *dest,
                                                             const GValue *value1,
                                                             const GValue *value2);

Calculates the intersection of two values. If the values have a non-empty intersection, the value representing the intersection is placed in `dest`. If the intersection is non-empty, `dest` is not modified.

`dest` : | a uninitialized GValue that will hold the calculated intersection value
`value1` : | a value to intersect
`value2` : | another value to intersect
Returns : | TRUE if the intersection is non-empty

### gst_value_can_intersect ()

    gboolean            gst_value_can_intersect             (const GValue *value1,
                                                             const GValue *value2);

Determines if intersecting two values will produce a valid result. Two values will produce a valid intersection if they have the same type, or if there is a method (registered by `gst_value_register_intersection_func()`) to calculate the intersection.

`value1` : | a value to intersect
`value2` : | another value to intersect
Returns : | TRUE if the values can intersect

### gst_value_register_intersect_func ()

    void                gst_value_register_intersect_func   (GType type1,
                                                             GType type2,
                                                             GstValueIntersectFunc func);

Registers a function that is called to calculate the intersection of the values having the types `type1` and `type2`.

Intersect functions should be registered at startup before any pipelines are started, as `gst_value_register_intersect_func()` is not thread-safe and cannot be used at the same time as `gst_value_intersect()` or `gst_value_can_intersect()`.

`type1` : | the first type to intersect
`type2` : | the second type to intersect
`func` : | the intersection function

### gst_value_array_append_value ()

    void                gst_value_array_append_value        (GValue *value,
                                                             const GValue *append_value);

Appends `append_value` to the GstValueArray in `value`.

`value` : | a GValue of type GST_TYPE_ARRAY
`append_value` : | the value to append

### gst_value_array_get_size ()

    guint               gst_value_array_get_size            (const GValue *value);

Gets the number of values contained in `value`.

`value` : | a GValue of type GST_TYPE_ARRAY
Returns : | the number of values

### gst_value_array_get_value ()

    const GValue*       gst_value_array_get_value           (const GValue *value,
                                                             guint index);

Gets the value that is a member of the array contained in `value` and has the index `index`.

`value` : | a GValue of type GST_TYPE_ARRAY
`index` : | index of value to get from the array
Returns : | the value at the given index

### gst_value_array_prepend_value ()

    void                gst_value_array_prepend_value       (GValue *value,
                                                             const GValue *prepend_value);

Prepends `prepend_value` to the GstValueArray in `value`.

`value` : | a GValue of type GST_TYPE_ARRAY
`prepend_value` : | the value to prepend