GstCaps

GstCaps — Structure describing sets of media formats

Synopsis


#include <gst/gst.h>


                    GstCaps;
                    GstStaticCaps;
enum                GstCapsFlags;
#define             GST_CAPS_ANY
#define             GST_CAPS_NONE
#define             GST_CAPS_REFCOUNT                   (caps)
#define             GST_CAPS_REFCOUNT_VALUE             (caps)
#define             GST_STATIC_CAPS_ANY
#define             GST_STATIC_CAPS_NONE
#define             GST_CAPS_IS_SIMPLE                  (caps)
#define             GST_DEBUG_CAPS                      (string, caps)
#define             GST_STATIC_CAPS                     (string)
GstCaps*            gst_caps_new_empty                  (void);
GstCaps*            gst_caps_new_any                    (void);
GstCaps*            gst_caps_new_simple                 (const char *media_type,
                                                         const char *fieldname,
                                                         ...);
GstCaps*            gst_caps_new_full                   (GstStructure *struct1,
                                                         ...);
GstCaps*            gst_caps_new_full_valist            (GstStructure *structure,
                                                         va_list var_args);
GstCaps*            gst_caps_copy                       (const GstCaps *caps);
GstCaps*            gst_caps_copy_nth                   (const GstCaps *caps,
                                                         guint nth);
GstCaps*            gst_static_caps_get                 (GstStaticCaps *static_caps);
void                gst_caps_append                     (GstCaps *caps1,
                                                         GstCaps *caps2);
void                gst_caps_merge                      (GstCaps *caps1,
                                                         GstCaps *caps2);
void                gst_caps_append_structure           (GstCaps *caps,
                                                         GstStructure *structure);
void                gst_caps_remove_structure           (GstCaps *caps,
                                                         guint idx);
void                gst_caps_merge_structure            (GstCaps *caps,
                                                         GstStructure *structure);
guint               gst_caps_get_size                   (const GstCaps *caps);
GstStructure*       gst_caps_get_structure              (const GstCaps *caps,
                                                         guint index);
void                gst_caps_set_simple                 (GstCaps *caps,
                                                         char *field,
                                                         ...);
void                gst_caps_set_simple_valist          (GstCaps *caps,
                                                         char *field,
                                                         va_list varargs);
gboolean            gst_caps_is_any                     (const GstCaps *caps);
gboolean            gst_caps_is_empty                   (const GstCaps *caps);
gboolean            gst_caps_is_fixed                   (const GstCaps *caps);
gboolean            gst_caps_is_equal                   (const GstCaps *caps1,
                                                         const GstCaps *caps2);
gboolean            gst_caps_is_equal_fixed             (const GstCaps *caps1,
                                                         const GstCaps *caps2);
gboolean            gst_caps_is_always_compatible       (const GstCaps *caps1,
                                                         const GstCaps *caps2);
gboolean            gst_caps_is_subset                  (const GstCaps *subset,
                                                         const GstCaps *superset);
GstCaps*            gst_caps_intersect                  (const GstCaps *caps1,
                                                         const GstCaps *caps2);
GstCaps*            gst_caps_union                      (const GstCaps *caps1,
                                                         const GstCaps *caps2);
GstCaps*            gst_caps_normalize                  (const GstCaps *caps);
gboolean            gst_caps_do_simplify                (GstCaps *caps);
xmlNodePtr          gst_caps_save_thyself               (const GstCaps *caps,
                                                         xmlNodePtr parent);
GstCaps*            gst_caps_load_thyself               (xmlNodePtr parent);
void                gst_caps_replace                    (GstCaps **caps,
                                                         GstCaps *newcaps);
gchar*              gst_caps_to_string                  (const GstCaps *caps);
GstCaps*            gst_caps_from_string                (const gchar *string);
GstCaps*            gst_caps_subtract                   (const GstCaps *minuend,
                                                         const GstCaps *subtrahend);
GstCaps*            gst_caps_make_writable              (GstCaps *caps);
GstCaps*            gst_caps_ref                        (GstCaps *caps);
void                gst_caps_truncate                   (GstCaps *caps);
void                gst_caps_unref                      (GstCaps *caps);


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 4. 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)

Details

GstCaps

typedef struct {
  GType type;

  /* refcounting */
  gint           refcount;

  GstCapsFlags flags;
} GstCaps;

Object describing media types.

GType type; GType of the caps
gint refcount; the atomic refcount value
GstCapsFlags flags; extra flags for the caps, read only.

GstStaticCaps

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

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.

GstCaps caps; the cached GstCaps
const char *string; a string describing a caps

enum GstCapsFlags

typedef enum {
  GST_CAPS_FLAGS_ANY	= (1 << 0)
} GstCapsFlags;

Extra flags for a caps.

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_CAPS_REFCOUNT()

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

Get access to the reference count field of the caps

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.

caps : a GstCaps

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.


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.

caps : the GstCaps instance to check

GST_DEBUG_CAPS()

#define             GST_DEBUG_CAPS(string, caps)

Warning

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().

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)

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

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

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

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.

media_type : the media type of the structure
fieldname : first field to set
... : additional arguments
Returns : the new GstCaps

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.

struct1 : the first structure to add
... : additional structures to add
Returns : the new GstCaps

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.

structure : the first structure to add
var_args : additional structures to add
Returns : the new GstCaps

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.

caps : the GstCaps to copy
Returns : the new GstCaps

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.

caps : the GstCaps to copy
nth : the nth structure to copy
Returns : the new GstCaps

gst_static_caps_get ()

GstCaps*            gst_static_caps_get                 (GstStaticCaps *static_caps);

Converts a GstStaticCaps to a GstCaps.

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.

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.

caps1 : the GstCaps that will be appended to
caps2 : the GstCaps to append

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.

caps1 : the GstCaps that will take the new entries
caps2 : the GstCaps to merge in

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.

caps : the GstCaps that will be appended to
structure : the GstStructure to append

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.

caps : the GstCaps to remove from
idx : Index of the structure to remove

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.

caps : the GstCaps that will the the new structure
structure : the GstStructure to merge

gst_caps_get_size ()

guint               gst_caps_get_size                   (const GstCaps *caps);

Gets the number of structures contained in caps.

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.

caps : a GstCaps
index : the index of the structure
Returns : a pointer to the GstStructure corresponding to index

gst_caps_set_simple ()

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

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.

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,
                                                         char *field,
                                                         va_list varargs);

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.

caps : the GstCaps to copy
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.

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.

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.

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.

Note

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.

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.

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.

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.

Note

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

subset : a GstCaps
superset : a potentially greater GstCaps
Returns : TRUE if subset is a subset of superset

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.

caps1 : a GstCaps to intersect
caps2 : a GstCaps to intersect
Returns : the new GstCaps

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.

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.

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.

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.

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.

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.

caps : a pointer to GstCaps
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.

caps : a GstCaps
Returns : a newly allocated string representing caps.

gst_caps_from_string ()

GstCaps*            gst_caps_from_string                (const gchar *string);

Converts caps from a string representation.

string : a string to convert to GstCaps
Returns : a newly allocated GstCaps

gst_caps_subtract ()

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

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.

minuend : GstCaps to substract from
subtrahend : GstCaps to substract
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().

caps : the GstCaps to make writable
Returns : the same GstCaps object.

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 gst_caps_new(), or via taking one explicitly with this function.

caps : the GstCaps to reference
Returns : the same GstCaps object.

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.

caps : the GstCaps to truncate

gst_caps_unref ()

void                gst_caps_unref                      (GstCaps *caps);

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

caps : the GstCaps to unref

See Also

GstStructure