GstCaps

GstCaps — Structure describing sets of media formats

Functions

#define GST_CAPS_REFCOUNT()
#define GST_CAPS_REFCOUNT_VALUE()
#define GST_CAPS_IS_SIMPLE()
#define GST_DEBUG_CAPS()
#define GST_STATIC_CAPS()
GstCaps * gst_caps_new_empty ()
GstCaps * gst_caps_new_any ()
GstCaps * gst_caps_new_simple ()
GstCaps * gst_caps_new_full ()
GstCaps * gst_caps_new_full_valist ()
GstCaps * gst_caps_copy ()
GstCaps * gst_caps_copy_nth ()
GstCaps * gst_static_caps_get ()
void gst_caps_append ()
void gst_caps_merge ()
void gst_caps_append_structure ()
void gst_caps_remove_structure ()
GstStructure * gst_caps_steal_structure ()
void gst_caps_merge_structure ()
guint gst_caps_get_size ()
GstStructure * gst_caps_get_structure ()
void gst_caps_set_value ()
void gst_caps_set_simple ()
void gst_caps_set_simple_valist ()
gboolean gst_caps_is_any ()
gboolean gst_caps_is_empty ()
gboolean gst_caps_is_fixed ()
gboolean gst_caps_is_equal ()
gboolean gst_caps_is_equal_fixed ()
gboolean gst_caps_is_always_compatible ()
gboolean gst_caps_is_subset ()
gboolean gst_caps_is_subset_structure ()
gboolean gst_caps_can_intersect ()
GstCaps * gst_caps_intersect ()
GstCaps * gst_caps_intersect_full ()
GstCaps * gst_caps_union ()
GstCaps * gst_caps_normalize ()
gboolean gst_caps_do_simplify ()
xmlNodePtr gst_caps_save_thyself ()
GstCaps * gst_caps_load_thyself ()
void gst_caps_replace ()
gchar * gst_caps_to_string ()
GstCaps * gst_caps_from_string ()
GstCaps * gst_caps_subtract ()
GstCaps * gst_caps_make_writable ()
GstCaps * gst_caps_ref ()
void gst_caps_truncate ()
void gst_caps_unref ()

Types and Values

Includes

#include <gst/gst.h>

Description

Caps (capabilities) are lighweight refcounted objects describing media types. They are composed of an array of GstStructure.

Caps are exposed on GstPadTemplate to describe all possible types a given pad can handle. They are also stored in the GstRegistry along with a description of the GstElement.

Caps are exposed on the element pads using the gst_pad_get_caps() pad function. This function describes the possible types that the pad can handle or produce at runtime.

Caps are also attached to buffers to describe to content of the data pointed to by the buffer with gst_buffer_set_caps(). Caps attached to a GstBuffer allow for format negotiation upstream and downstream.

A GstCaps can be constructed with the following code fragment:

Example 7. Creating caps

 GstCaps *caps;
 caps = gst_caps_new_simple ("video/x-raw-yuv",
      "format", GST_TYPE_FOURCC, GST_MAKE_FOURCC ('I', '4', '2', '0'),
      "framerate", GST_TYPE_FRACTION, 25, 1,
      "pixel-aspect-ratio", GST_TYPE_FRACTION, 1, 1,
      "width", G_TYPE_INT, 320,
      "height", G_TYPE_INT, 240,
      NULL);
 

A GstCaps is fixed when it has no properties with ranges or lists. Use gst_caps_is_fixed() to test for fixed caps. Only fixed caps can be set on a GstPad or GstBuffer.

Various methods exist to work with the media types such as subtracting or intersecting.

Last reviewed on 2007-02-13 (0.10.10)

Functions

GST_CAPS_REFCOUNT()

#define GST_CAPS_REFCOUNT(caps)                 ((GST_CAPS(caps))->refcount)

Get access to the reference count field of the caps

Parameters

caps

a GstCaps

 

GST_CAPS_REFCOUNT_VALUE()

#define GST_CAPS_REFCOUNT_VALUE(caps)           (g_atomic_int_get (&(GST_CAPS(caps))->refcount))

Get the reference count value of the caps.

Parameters

caps

a GstCaps

 

GST_CAPS_IS_SIMPLE()

#define GST_CAPS_IS_SIMPLE(caps) (gst_caps_get_size(caps) == 1)

Convenience macro that checks if the number of structures in the given caps is exactly one.

Parameters

caps

the GstCaps instance to check

 

GST_DEBUG_CAPS()

#define             GST_DEBUG_CAPS(string, caps)

GST_DEBUG_CAPS is deprecated and should not be used in newly-written code.

do not use anymore

Convenience macro for printing out the contents of caps with GST_DEBUG().

Parameters

string

a string that should be prepended to the caps data.

 

caps

the GstCaps instance to print

 

GST_STATIC_CAPS()

#define             GST_STATIC_CAPS(string)

GST_STATIC_CAPS is deprecated and should not be used in newly-written code.

Creates a new GstCaps static caps from an input string. This can be used in pad templates.

Parameters

string

the string describing the caps

 

gst_caps_new_empty ()

GstCaps *
gst_caps_new_empty (void);

Creates a new GstCaps that is empty. That is, the returned GstCaps contains no media formats. Caller is responsible for unreffing the returned caps.

Returns

the new GstCaps.

[transfer full]


gst_caps_new_any ()

GstCaps *
gst_caps_new_any (void);

Creates a new GstCaps that indicates that it is compatible with any media format.

Returns

the new GstCaps.

[transfer full]


gst_caps_new_simple ()

GstCaps *
gst_caps_new_simple (const char *media_type,
                     const char *fieldname,
                     ...);

Creates a new GstCaps that contains one GstStructure. The structure is defined by the arguments, which have the same format as gst_structure_new(). Caller is responsible for unreffing the returned caps.

Parameters

media_type

the media type of the structure

 

fieldname

first field to set

 

...

additional arguments

 

Returns

the new GstCaps.

[transfer full]


gst_caps_new_full ()

GstCaps *
gst_caps_new_full (GstStructure *struct1,
                   ...);

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.

Parameters

struct1

the first structure to add

 

...

additional structures to add

 

Returns

the new GstCaps.

[transfer full]


gst_caps_new_full_valist ()

GstCaps *
gst_caps_new_full_valist (GstStructure *structure,
                          va_list var_args);

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.

Parameters

structure

the first structure to add

 

var_args

additional structures to add

 

Returns

the new GstCaps.

[transfer full]


gst_caps_copy ()

GstCaps *
gst_caps_copy (const GstCaps *caps);

Creates a new GstCaps as a copy of the old caps . The new caps will have a refcount of 1, owned by the caller. The structures are copied as well.

Note that this function is the semantic equivalent of a gst_caps_ref() followed by a gst_caps_make_writable(). If you only want to hold on to a reference to the data, you should use gst_caps_ref().

When you are finished with the caps, call gst_caps_unref() on it.

Parameters

caps

the GstCaps to copy

 

Returns

the new GstCaps.

[transfer full]


gst_caps_copy_nth ()

GstCaps *
gst_caps_copy_nth (const GstCaps *caps,
                   guint nth);

Creates a new GstCaps and appends a copy of the nth structure contained in caps .

Parameters

caps

the GstCaps to copy

 

nth

the nth structure to copy

 

Returns

the new GstCaps.

[transfer full]


gst_static_caps_get ()

GstCaps *
gst_static_caps_get (GstStaticCaps *static_caps);

Converts a GstStaticCaps to a GstCaps.

Parameters

static_caps

the GstStaticCaps to convert

 

Returns

a pointer to the GstCaps. Unref after usage. Since the core holds an additional ref to the returned caps, use gst_caps_make_writable() on the returned caps to modify it.

[transfer full]


gst_caps_append ()

void
gst_caps_append (GstCaps *caps1,
                 GstCaps *caps2);

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. If either caps is ANY, the resulting caps will be ANY.

Parameters

caps1

the GstCaps that will be appended to

 

caps2

the GstCaps to append.

[transfer full]

gst_caps_merge ()

void
gst_caps_merge (GstCaps *caps1,
                GstCaps *caps2);

Appends the structures contained in caps2 to caps1 if they are not yet expressed by caps1 . The structures in caps2 are not copied -- they are transferred to caps1 , and then caps2 is freed. If either caps is ANY, the resulting caps will be ANY.

Parameters

caps1

the GstCaps that will take the new entries

 

caps2

the GstCaps to merge in.

[transfer full]

Since 0.10.10


gst_caps_append_structure ()

void
gst_caps_append_structure (GstCaps *caps,
                           GstStructure *structure);

Appends structure to caps . The structure is not copied; caps becomes the owner of structure .

Parameters

caps

the GstCaps that will be appended to

 

structure

the GstStructure to append.

[transfer full]

gst_caps_remove_structure ()

void
gst_caps_remove_structure (GstCaps *caps,
                           guint idx);

removes the stucture with the given index from the list of structures contained in caps .

Parameters

caps

the GstCaps to remove from

 

idx

Index of the structure to remove

 

gst_caps_steal_structure ()

GstStructure *
gst_caps_steal_structure (GstCaps *caps,
                          guint index);

Retrieves the stucture with the given index from the list of structures contained in caps . The caller becomes the owner of the returned structure.

Parameters

caps

the GstCaps to retrieve from

 

index

Index of the structure to retrieve

 

Returns

a pointer to the GstStructure corresponding to index .

[transfer full]

Since 0.10.30


gst_caps_merge_structure ()

void
gst_caps_merge_structure (GstCaps *caps,
                          GstStructure *structure);

Appends structure to caps if its not already expressed by caps . The structure is not copied; caps becomes the owner of structure .

Parameters

caps

the GstCaps that will the new structure

 

structure

the GstStructure to merge.

[transfer full]

gst_caps_get_size ()

guint
gst_caps_get_size (const GstCaps *caps);

Gets the number of structures contained in caps .

Parameters

caps

a GstCaps

 

Returns

the number of structures that caps contains


gst_caps_get_structure ()

GstStructure *
gst_caps_get_structure (const GstCaps *caps,
                        guint index);

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. However, if you know the caps are writable, either because you have just copied them or made them writable with gst_caps_make_writable(), you may modify the structure returned in the usual way, e.g. with functions like gst_structure_set().

You do not need to free or unref the structure returned, it belongs to the GstCaps.

Parameters

caps

a GstCaps

 

index

the index of the structure

 

Returns

a pointer to the GstStructure corresponding to index .

[transfer none]


gst_caps_set_value ()

void
gst_caps_set_value (GstCaps *caps,
                    const char *field,
                    const GValue *value);

Sets the given field on all structures of caps to the given value . This is a convenience function for calling gst_structure_set_value() on all structures of caps .

Parameters

caps

a writable caps

 

field

name of the field to set

 

value

value to set the field to

 

Since 0.10.26


gst_caps_set_simple ()

void
gst_caps_set_simple (GstCaps *caps,
                     const char *field,
                     ...);

Sets fields in a GstCaps. The arguments must be passed in the same manner as gst_structure_set(), and be NULL-terminated.

Prior to GStreamer version 0.10.26, this function failed when caps was not simple. If your code needs to work with those versions of GStreamer, you may only call this function when GST_CAPS_IS_SIMPLE() is TRUE for caps.

Parameters

caps

the GstCaps to set

 

field

first field to set

 

...

additional parameters

 

gst_caps_set_simple_valist ()

void
gst_caps_set_simple_valist (GstCaps *caps,
                            const char *field,
                            va_list varargs);

Sets fields in a GstCaps. The arguments must be passed in the same manner as gst_structure_set(), and be NULL-terminated.

Prior to GStreamer version 0.10.26, this function failed when caps was not simple. If your code needs to work with those versions of GStreamer, you may only call this function when GST_CAPS_IS_SIMPLE() is TRUE for caps.

Parameters

caps

the GstCaps to set

 

field

first field to set

 

varargs

additional parameters

 

gst_caps_is_any ()

gboolean
gst_caps_is_any (const GstCaps *caps);

Determines if caps represents any media format.

Parameters

caps

the GstCaps to test

 

Returns

TRUE if caps represents any format.


gst_caps_is_empty ()

gboolean
gst_caps_is_empty (const GstCaps *caps);

Determines if caps represents no media formats.

Parameters

caps

the GstCaps to test

 

Returns

TRUE if caps represents no formats.


gst_caps_is_fixed ()

gboolean
gst_caps_is_fixed (const GstCaps *caps);

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.

Parameters

caps

the GstCaps to test

 

Returns

TRUE if caps is fixed


gst_caps_is_equal ()

gboolean
gst_caps_is_equal (const GstCaps *caps1,
                   const GstCaps *caps2);

Checks if the given caps represent the same set of caps.

This function does not work reliably if optional properties for caps are included on one caps and omitted on the other.

This function deals correctly with passing NULL for any of the caps.

Parameters

caps1

a GstCaps

 

caps2

another GstCaps

 

Returns

TRUE if both caps are equal.


gst_caps_is_equal_fixed ()

gboolean
gst_caps_is_equal_fixed (const GstCaps *caps1,
                         const GstCaps *caps2);

Tests if two GstCaps are equal. This function only works on fixed GstCaps.

Parameters

caps1

the GstCaps to test

 

caps2

the GstCaps to test

 

Returns

TRUE if the arguments represent the same format


gst_caps_is_always_compatible ()

gboolean
gst_caps_is_always_compatible (const GstCaps *caps1,
                               const GstCaps *caps2);

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 .

Parameters

caps1

the GstCaps to test

 

caps2

the GstCaps to test

 

Returns

TRUE if caps1 is a subset of caps2 .


gst_caps_is_subset ()

gboolean
gst_caps_is_subset (const GstCaps *subset,
                    const GstCaps *superset);

Checks if all caps represented by subset are also represented by superset .

This function does not work reliably if optional properties for caps are included on one caps and omitted on the other.

Parameters

subset

a GstCaps

 

superset

a potentially greater GstCaps

 

Returns

TRUE if subset is a subset of superset


gst_caps_is_subset_structure ()

gboolean
gst_caps_is_subset_structure (const GstCaps *caps,
                              const GstStructure *structure);

Checks if structure is a subset of caps . See gst_caps_is_subset() for more information.

Parameters

caps

a GstCaps

 

structure

a potential GstStructure subset of caps

 

Returns

TRUE if structure is a subset of caps

Since 0.10.36


gst_caps_can_intersect ()

gboolean
gst_caps_can_intersect (const GstCaps *caps1,
                        const GstCaps *caps2);

Tries intersecting caps1 and caps2 and reports whether the result would not be empty

Parameters

caps1

a GstCaps to intersect

 

caps2

a GstCaps to intersect

 

Returns

TRUE if intersection would be not empty

Since 0.10.25


gst_caps_intersect ()

GstCaps *
gst_caps_intersect (const GstCaps *caps1,
                    const GstCaps *caps2);

Creates a new GstCaps that contains all the formats that are common to both caps1 and caps2 . Defaults to GST_CAPS_INTERSECT_ZIG_ZAG mode.

Parameters

caps1

a GstCaps to intersect

 

caps2

a GstCaps to intersect

 

Returns

the new GstCaps


gst_caps_intersect_full ()

GstCaps *
gst_caps_intersect_full (const GstCaps *caps1,
                         const GstCaps *caps2,
                         GstCapsIntersectMode mode);

Creates a new GstCaps that contains all the formats that are common to both caps1 and caps2 , the order is defined by the GstCapsIntersectMode used.

Parameters

caps1

a GstCaps to intersect

 

caps2

a GstCaps to intersect

 

mode

The intersection algorithm/mode to use

 

Returns

the new GstCaps

Since 0.10.33


gst_caps_union ()

GstCaps *
gst_caps_union (const GstCaps *caps1,
                const GstCaps *caps2);

Creates a new GstCaps that contains all the formats that are in either caps1 and caps2 .

Parameters

caps1

a GstCaps to union

 

caps2

a GstCaps to union

 

Returns

the new GstCaps


gst_caps_normalize ()

GstCaps *
gst_caps_normalize (const GstCaps *caps);

Creates a new GstCaps that represents the same set of formats as caps , but contains no lists. Each list is expanded into separate GstStructures .

Parameters

caps

a GstCaps to normalize

 

Returns

the new GstCaps


gst_caps_do_simplify ()

gboolean
gst_caps_do_simplify (GstCaps *caps);

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.

Parameters

caps

a GstCaps to simplify

 

Returns

TRUE, if the caps could be simplified


gst_caps_save_thyself ()

xmlNodePtr
gst_caps_save_thyself (const GstCaps *caps,
                       xmlNodePtr parent);

Serializes a GstCaps to XML and adds it as a child node of parent .

Parameters

caps

a GstCaps structure

 

parent

a XML parent node

 

Returns

a XML node pointer


gst_caps_load_thyself ()

GstCaps *
gst_caps_load_thyself (xmlNodePtr parent);

Creates a GstCaps from its XML serialization.

Parameters

parent

a XML node

 

Returns

a new GstCaps structure


gst_caps_replace ()

void
gst_caps_replace (GstCaps **caps,
                  GstCaps *newcaps);

Replaces *caps with newcaps . Unrefs the GstCaps in the location pointed to by caps , if applicable, then modifies caps to point to newcaps . An additional ref on newcaps is taken.

This function does not take any locks so you might want to lock the object owning caps pointer.

Parameters

caps

a pointer to GstCaps.

[inout][transfer full]

newcaps

a GstCaps to replace *caps

 

gst_caps_to_string ()

gchar *
gst_caps_to_string (const GstCaps *caps);

Converts caps to a string representation. This string representation can be converted back to a GstCaps by gst_caps_from_string().

For debugging purposes its easier to do something like this:

GST_LOG ("caps are %" GST_PTR_FORMAT, caps);

This prints the caps in human readble form.

Parameters

caps

a GstCaps

 

Returns

a newly allocated string representing caps .

[transfer full]


gst_caps_from_string ()

GstCaps *
gst_caps_from_string (const gchar *string);

Converts caps from a string representation.

Parameters

string

a string to convert to GstCaps

 

Returns

a newly allocated GstCaps.

[transfer full]


gst_caps_subtract ()

GstCaps *
gst_caps_subtract (const GstCaps *minuend,
                   const GstCaps *subtrahend);

Subtracts the subtrahend from the minuend .

This function does not work reliably if optional properties for caps are included on one caps and omitted on the other.

Parameters

minuend

GstCaps to subtract from

 

subtrahend

GstCaps to subtract

 

Returns

the resulting caps


gst_caps_make_writable ()

GstCaps *
gst_caps_make_writable (GstCaps *caps);

Returns a writable copy of caps .

If there is only one reference count on caps , the caller must be the owner, and so this function will return the caps object unchanged. If on the other hand there is more than one reference on the object, a new caps object will be returned. The caller's reference on caps will be removed, and instead the caller will own a reference to the returned object.

In short, this function unrefs the caps in the argument and refs the caps that it returns. Don't access the argument after calling this function. See also: gst_caps_ref().

Parameters

caps

the GstCaps to make writable.

[transfer full]

Returns

the same GstCaps object.

[transfer full]


gst_caps_ref ()

GstCaps *
gst_caps_ref (GstCaps *caps);

Add a reference to a GstCaps object.

From this point on, until the caller calls gst_caps_unref() or gst_caps_make_writable(), it is guaranteed that the caps object will not change. This means its structures won't change, etc. To use a GstCaps object, you must always have a refcount on it -- either the one made implicitly by e.g. gst_caps_new_simple(), or via taking one explicitly with this function.

Parameters

caps

the GstCaps to reference

 

Returns

the same GstCaps object.

[transfer full]


gst_caps_truncate ()

void
gst_caps_truncate (GstCaps *caps);

Destructively discard all but the first structure from caps . Useful when fixating. caps must be writable.

Parameters

caps

the GstCaps to truncate

 

gst_caps_unref ()

void
gst_caps_unref (GstCaps *caps);

Unref a GstCaps and free all its structures and the structures' values when the refcount reaches 0.

Parameters

caps

the GstCaps to unref.

[transfer full]

Types and Values

struct GstCaps

struct GstCaps {
  GType type;

  /* refcounting */
  gint           refcount;

  GstCapsFlags flags;
};

Object describing media types.

Members

GType type;

GType of the caps

 

gint refcount;

the atomic refcount value

 

GstCapsFlags flags;

extra flags for the caps, read only.

 

struct GstStaticCaps

struct GstStaticCaps {
  GstCaps caps;
  const char *string;
};

Datastructure to initialize GstCaps from a string description usually used in conjunction with GST_STATIC_CAPS() and gst_static_caps_get() to instantiate a GstCaps.

Members

GstCaps caps;

the cached GstCaps

 

const char *string;

a string describing a caps

 

enum GstCapsIntersectMode

Modes of caps intersection

GST_CAPS_INTERSECT_ZIG_ZAG tries to preserve overall order of both caps by iterating on the caps' structures as the following matrix shows:

         caps1
      +-------------
      | 1  2  4  7
caps2 | 3  5  8 10
      | 6  9 11 12

Used when there is no explicit precedence of one caps over the other. e.g. tee's sink pad getcaps function, it will probe its src pad peers' for their caps and intersect them with this mode.

GST_CAPS_INTERSECT_FIRST is useful when an element wants to preserve another element's caps priority order when intersecting with its own caps. Example: If caps1 is [A, B, C] and caps2 is [E, B, D, A], the result would be [A, B], maintaining the first caps priority on the intersection.

Members

GST_CAPS_INTERSECT_ZIG_ZAG

Zig-zags over both caps.

 

GST_CAPS_INTERSECT_FIRST

Keeps the first caps order.

 

Since 0.10.33


enum GstCapsFlags

Extra flags for a caps.

Members

GST_CAPS_FLAGS_NONE

no extra flags (Since 0.10.36)

 

GST_CAPS_FLAGS_ANY

Caps has no specific content, but can contain anything.

 

GST_CAPS_ANY

#define GST_CAPS_ANY              gst_caps_new_any()

Means that the element/pad can output 'anything'. Useful for elements that output unknown media, such as filesrc.


GST_CAPS_NONE

#define GST_CAPS_NONE             gst_caps_new_empty()

The opposite of GST_CAPS_ANY: it means that the pad/element outputs an undefined media type that can not be detected.


GST_STATIC_CAPS_ANY

#define GST_STATIC_CAPS_ANY       GST_STATIC_CAPS("ANY")

Creates a new GstCaps static caps that matches anything. This can be used in pad templates.


GST_STATIC_CAPS_NONE

#define GST_STATIC_CAPS_NONE      GST_STATIC_CAPS("NONE")

Creates a new GstCaps static caps that matches nothing. This can be used in pad templates.

See Also

GstStructure