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GStreamer 1.0 Core Reference Manual | ![]() |
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Top | Description |
#include <gst/gst.h> struct GstCaps; struct GstStaticCaps; enum GstCapsIntersectMode; 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_STATIC_CAPS (string) #define GST_CAPS_FLAGS (caps) #define GST_CAPS_FLAG_IS_SET (caps, flag) #define GST_CAPS_FLAG_SET (caps, flag) #define GST_CAPS_FLAG_UNSET (caps, flag) GstCaps * gst_caps_new_empty (void
); GstCaps * gst_caps_new_empty_simple (const char *media_type
); 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
); #define gst_caps_is_writable (caps) 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_static_caps_cleanup (GstStaticCaps *static_caps
); void gst_caps_append (GstCaps *caps1
,GstCaps *caps2
); GstCaps * 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
); GstStructure * gst_caps_steal_structure (GstCaps *caps
,guint index
); GstCaps * 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_value (GstCaps *caps
,const char *field
,const GValue *value
); void gst_caps_set_simple (GstCaps *caps
,const char *field
,...
); void gst_caps_set_simple_valist (GstCaps *caps
,const 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_strictly_equal (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
); gboolean gst_caps_is_subset_structure (const GstCaps *caps
,const GstStructure *structure
); gboolean gst_caps_can_intersect (const GstCaps *caps1
,const GstCaps *caps2
); GstCaps * gst_caps_intersect (GstCaps *caps1
,GstCaps *caps2
); GstCaps * gst_caps_intersect_full (GstCaps *caps1
,GstCaps *caps2
,GstCapsIntersectMode mode
); GstCaps * gst_caps_normalize (GstCaps *caps
); GstCaps * gst_caps_simplify (GstCaps *caps
); gboolean gst_caps_replace (GstCaps **old_caps
,GstCaps *new_caps
); gboolean gst_caps_take (GstCaps **old_caps
,GstCaps *new_caps
); gchar * gst_caps_to_string (const GstCaps *caps
); GstCaps * gst_caps_from_string (const gchar *string
); GstCaps * gst_caps_subtract (GstCaps *minuend
,GstCaps *subtrahend
); #define gst_caps_make_writable (caps) GstCaps * gst_caps_truncate (GstCaps *caps
); GstCaps * gst_caps_fixate (GstCaps *caps
); GstCaps * gst_caps_ref (GstCaps *caps
); void gst_caps_unref (GstCaps *caps
);
Caps (capabilities) are lightweight 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_query_caps()
pad
function. This function describes the possible types that the pad can
handle or produce at runtime.
A GstCaps can be constructed with the following code fragment:
Example 4. Creating caps
1 2 3 4 5 6 7 8 |
GstCaps *caps; caps = gst_caps_new_simple ("video/x-raw", "format", G_TYPE_STRING, "I420", "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. Fixed caps can be used in a
caps event to notify downstream elements of the current media type.
Various methods exist to work with the media types such as subtracting or intersecting.
Last reviewed on 2011-03-28 (0.11.3)
struct GstCaps { GstMiniObject mini_object; };
Object describing media types.
GstMiniObject |
the parent type |
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.
typedef enum { GST_CAPS_INTERSECT_ZIG_ZAG = 0, GST_CAPS_INTERSECT_FIRST = 1 } 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:
1 2 3 4 5 |
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.
typedef enum { GST_CAPS_FLAG_ANY = (GST_MINI_OBJECT_FLAG_LAST << 0) } GstCapsFlags;
Extra flags for a caps.
#define GST_CAPS_ANY _gst_caps_any
Means that the element/pad can output 'anything'. Useful for elements that output unknown media, such as filesrc. This macro returns a singleton and should not be unreffed.
#define GST_CAPS_NONE _gst_caps_none
The opposite of GST_CAPS_ANY
: it means that the pad/element outputs an
undefined media type that can not be detected. This macro returns a singleton
and should not be unreffed.
#define GST_CAPS_REFCOUNT(caps) GST_MINI_OBJECT_REFCOUNT(caps)
Get access to the reference count field of the caps
|
a GstCaps |
#define GST_CAPS_REFCOUNT_VALUE(caps) GST_MINI_OBJECT_REFCOUNT_VALUE(caps)
Get the reference count value of the caps.
|
a GstCaps |
#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.
#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.
#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.
|
the GstCaps instance to check |
#define GST_STATIC_CAPS(string)
Creates a new GstCaps static caps from an input string. This can be used in pad templates.
|
the string describing the caps |
#define GST_CAPS_FLAGS(caps) GST_MINI_OBJECT_FLAGS(caps)
A flags word containing GstCapsFlags flags set on this caps.
|
a GstCaps. |
#define GST_CAPS_FLAG_IS_SET(caps,flag) GST_MINI_OBJECT_FLAG_IS_SET (caps, flag)
Gives the status of a specific flag on a caps.
|
a GstCaps. |
|
the GstCapsFlags to check. |
#define GST_CAPS_FLAG_SET(caps,flag) GST_MINI_OBJECT_FLAG_SET (caps, flag)
Sets a caps flag on a caps.
|
a GstCaps. |
|
the GstCapsFlags to set. |
#define GST_CAPS_FLAG_UNSET(caps,flag) GST_MINI_OBJECT_FLAG_UNSET (caps, flag)
Clears a caps flag.
|
a GstCaps. |
|
the GstCapsFlags to clear. |
GstCaps * gst_caps_new_empty (void
);
Creates a new GstCaps that is empty. That is, the returned GstCaps contains no media formats. The GstCaps is guaranteed to be writable. Caller is responsible for unreffing the returned caps.
Returns : |
the new GstCaps. [transfer full] |
GstCaps * gst_caps_new_empty_simple (const char *media_type
);
Creates a new GstCaps that contains one GstStructure with name
media_type
.
Caller is responsible for unreffing the returned caps.
|
the media type of the structure |
Returns : |
the new GstCaps. [transfer full] |
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] |
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.
|
the media type of the structure |
|
first field to set |
|
additional arguments |
Returns : |
the new GstCaps. [transfer 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.
|
the first structure to add |
|
additional structures to add |
Returns : |
the new GstCaps. [transfer full] |
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.
|
the first structure to add |
|
additional structures to add |
Returns : |
the new GstCaps. [transfer full] |
#define gst_caps_is_writable(caps) gst_mini_object_is_writable (GST_MINI_OBJECT_CAST (caps))
Tests if you can safely modify caps
. It is only safe to modify caps when
there is only one owner of the caps - ie, the object is writable.
|
a GstCaps |
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.
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
.
GstCaps * gst_static_caps_get (GstStaticCaps *static_caps
);
Converts a GstStaticCaps to a GstCaps.
|
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]
|
void gst_static_caps_cleanup (GstStaticCaps *static_caps
);
Clean up the cached caps contained in static_caps
.
|
the GstStaticCaps to clean |
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.
GstCaps * 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 a writable copy of caps1
, and then caps2
is freed.
If either caps is ANY, the resulting caps will be ANY.
void gst_caps_append_structure (GstCaps *caps
,GstStructure *structure
);
Appends structure
to caps
. The structure is not copied; caps
becomes the owner of structure
.
|
the GstCaps that will be appended to |
|
the GstStructure to append. [transfer full] |
void gst_caps_remove_structure (GstCaps *caps
,guint idx
);
removes the stucture with the given index from the list of structures
contained in caps
.
|
the GstCaps to remove from |
|
Index of the structure to remove |
GstStructure * gst_caps_steal_structure (GstCaps *caps
,guint index
);
Retrieves the structure with the given index from the list of structures
contained in caps
. The caller becomes the owner of the returned structure.
|
the GstCaps to retrieve from |
|
Index of the structure to retrieve |
Returns : |
a pointer to the GstStructure corresponding
to index . [transfer full]
|
GstCaps * gst_caps_merge_structure (GstCaps *caps
,GstStructure *structure
);
Appends structure
to caps
if its not already expressed by caps
.
|
the GstCaps to merge into. [transfer full] |
|
the GstStructure to merge. [transfer full] |
Returns : |
the merged caps. [transfer full] |
guint gst_caps_get_size (const GstCaps *caps
);
Gets the number of structures contained in caps
.
|
a GstCaps |
Returns : |
the number of structures that caps contains |
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.
|
a GstCaps |
|
the index of the structure |
Returns : |
a pointer to the GstStructure corresponding
to index . [transfer none]
|
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
.
|
a writable caps |
|
name of the field to set |
|
value to set the field to |
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.
|
the GstCaps to set |
|
first field to set |
|
additional parameters |
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.
|
the GstCaps to set |
|
first field to set |
|
additional parameters |
gboolean gst_caps_is_any (const GstCaps *caps
);
Determines if caps
represents any media format.
|
the GstCaps to test |
Returns : |
TRUE if caps represents any format. |
gboolean gst_caps_is_empty (const GstCaps *caps
);
Determines if caps
represents no media formats.
|
the GstCaps to test |
Returns : |
TRUE if caps represents no formats. |
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.
|
the GstCaps to test |
Returns : |
TRUE if caps is fixed |
gboolean gst_caps_is_equal (const GstCaps *caps1
,const GstCaps *caps2
);
Checks if the given caps represent the same set of caps.
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.
gboolean gst_caps_is_strictly_equal (const GstCaps *caps1
,const GstCaps *caps2
);
Checks if the given caps are exactly the same set of caps.
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
.
gboolean gst_caps_is_subset (const GstCaps *subset
,const GstCaps *superset
);
Checks if all caps represented by subset
are also represented by superset
.
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.
|
a GstCaps |
|
a potential GstStructure subset of caps
|
Returns : |
TRUE if structure is a subset of caps
|
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
GstCaps * gst_caps_intersect (GstCaps *caps1
,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.
GstCaps * gst_caps_intersect_full (GstCaps *caps1
,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.
GstCaps * gst_caps_normalize (GstCaps *caps
);
Returns a GstCaps that represents the same set of formats as
caps
, but contains no lists. Each list is expanded into separate
GstStructures
.
This function takes ownership of caps
.
GstCaps * gst_caps_simplify (GstCaps *caps
);
Converts the given caps
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.
This method does not preserve the original order of caps
.
|
a GstCaps to simplify. [transfer full] |
Returns : |
The simplified caps. |
gboolean gst_caps_replace (GstCaps **old_caps
,GstCaps *new_caps
);
Modifies a pointer to a GstCaps to point to a different GstCaps. The modification is done atomically (so this is useful for ensuring thread safety in some cases), and the reference counts are updated appropriately (the old caps is unreffed, the new is reffed).
Either ncaps
or the GstCaps pointed to by ocaps
may be NULL.
gboolean gst_caps_take (GstCaps **old_caps
,GstCaps *new_caps
);
Modifies a pointer to a GstCaps to point to a different GstCaps. This
function is similar to gst_caps_replace()
except that it takes ownership
of new_caps
.
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:
1 |
GST_LOG ("caps are %" GST_PTR_FORMAT, caps); |
This prints the caps in human readable form.
|
a GstCaps |
Returns : |
a newly allocated string representing caps . [transfer full]
|
GstCaps * gst_caps_from_string (const gchar *string
);
Converts caps
from a string representation.
GstCaps * gst_caps_subtract (GstCaps *minuend
,GstCaps *subtrahend
);
Subtracts the subtrahend
from the minuend
.
#define gst_caps_make_writable(caps) GST_CAPS_CAST (gst_mini_object_make_writable (GST_MINI_OBJECT_CAST (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()
.
|
a GstCaps. [transfer full] |
Returns : |
a writable caps which may or may not be the
same as caps . [transfer full]
|
GstCaps * gst_caps_truncate (GstCaps *caps
);
Discard all but the first structure from caps
. Useful when
fixating.
|
the GstCaps to truncate. [transfer full] |
Returns : |
truncated caps. [transfer full] |
GstCaps * gst_caps_fixate (GstCaps *caps
);
Modifies the given caps
into a representation with only fixed
values. First the caps will be truncated and then the first structure will be
fixated with gst_structure_fixate()
.
|
a GstCaps to fixate. [transfer full] |
Returns : |
the fixated caps. [transfer full] |
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.