gstreamer插件所用函数整理
2016-10-06 08:30:46
（一）设置插件属性相关的函数：
（1） g_param_spec_boolean ()
函数链接如下：
https://developer.gnome.org/gobject/stable/gobject-Standard-Parameter-and-Value-Types.html
g_param_spec_boolean (const gchar *name,
constgchar *nick,
constgchar *blurb,
gboolean default_value,
GParamFlags flags);
Createsa new GParamSpecBooleaninstance specifying a G_TYPE_BOOLEAN property. In many cases,it may be more appropriate to use an enum with g_param_spec_enum(), both to improvecode clarity by using explicitly named values, and to allow for more values tobe added in future without breaking API.
See g_param_spec_internal() for details on property names.
Parameters
| name |
canonical name of the property specified |
|
| nick |
nick name for the property specified |
|
| blurb |
description of the property specified |
|
| default_value |
default value for the property specified |
|
| flags |
flags for the property specified |
Returns
anewly created parameter specification.
（2） g_param_spec_internal ()
上个函数中标红的 g_param_spec_internal函数的解释，链接如下：
https://developer.gnome.org/gobject/stable/gobject-GParamSpec.html#g-param-spec-internal
g_param_spec_internal (GType param_type,
const gchar *name,
constgchar *nick,
constgchar *blurb,
GParamFlags flags);
Createsa new GParamSpecinstance.
Aproperty name consists of segments consisting of ASCII letters and digits,separated by either the '-' or '_' character. The first character of a propertyname must be a letter. Names which violate these rules lead to undefinedbehaviour.
Whencreating and looking up a GParamSpec, either separator can be used, but theycannot be mixed. Using '-' is considerably more efficient and in fact requiredwhen using property names as detail strings for signals.
Beyondthe name, GParamSpecs have two more descriptive stringsassociated with them, the nick , which should be suitable for use as alabel for the property in a property editor, and the blurb , which should be a somewhat longer description,suitable for e.g. a tooltip. The nick and blurb should ideally be localized.
[skip]
Parameters
| param_type |
the GType for the property; must be derived from G_TYPE_PARAM |
|
| name |
the canonical name of the property |
|
| nick |
the nickname of the property |
|
| blurb |
a short description of the property |
|
| flags |
a combination of GParamFlags |
Returns
anewly allocated GParamSpec instance.
（3） enum GparamFlags
上面 g_param_spec_internal函数中标红的GParamFlags， 链接如下：
https://developer.gnome.org/gobject/stable/gobject-GParamSpec.html#GParamFlags
Throughthe GParamFlagsflag values, certain aspects of parameters can be configured. See also G_PARAM_STATIC_STRINGS.
Members
| the parameter is readable |
||
| the parameter is writable |
||
| alias for G_PARAM_READABLE | G_PARAM_WRITABLE |
||
| the parameter will be set upon object construction |
||
| the parameter can only be set upon object construction |
||
| upon parameter conversion (see g_param_value_convert()) strict validation is not required |
||
| the string used as name when constructing the parameter is guaranteed to remain valid and unmodified for the lifetime of the parameter. Since 2.8 |
||
| internal |
||
| the string used as nick when constructing the parameter is guaranteed to remain valid and unmmodified for the lifetime of the parameter. Since 2.8 |
||
| the string used as blurb when constructing the parameter is guaranteed to remain valid and unmodified for the lifetime of the parameter. Since 2.8 |
||
| calls to g_object_set_property() for this property will not automatically result in a "notify" signal being emitted: the implementation must call g_object_notify() themselves in case the property actually changes. Since: 2.42. |
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| the parameter is deprecated and will be removed in a future version. A warning will be generated if it is used while running with G_ENABLE_DIAGNOSTIC=1. Since 2.26 |
平时在使用过程中，flags参数有一个G_PARAM_STATIC_STRINGS，但是在上面的表格中并没有发现这个参数，继续在这个页面中向下查看，可以看到：
G_PARAM_STATIC_STRINGS
#defineG_PARAM_STATIC_STRINGS (G_PARAM_STATIC_NAME | G_PARAM_STATIC_NICK |G_PARAM_STATIC_BLURB)
GParamFlags value alias for G_PARAM_STATIC_NAME | G_PARAM_STATIC_NICK | G_PARAM_STATIC_BLURB.
Since2.13.0
（4） g_param_spec_boolean ()
链接如下：
g_param_spec_boolean (const gchar *name,
constgchar *nick,
const gchar *blurb,
gboolean default_value,
GParamFlags flags);
Createsa new GParamSpecBooleaninstance specifying a G_TYPE_BOOLEAN property. In many cases,it may be more appropriate to use an enum with g_param_spec_enum(), both to improvecode clarity by using explicitly named values, and to allow for more values tobe added in future without breaking API.
See g_param_spec_internal() for details on property names.
Parameters
| name |
canonical name of the property specified |
|
| nick |
nick name for the property specified |
|
| blurb |
description of the property specified |
|
| default_value |
default value for the property specified |
|
| flags |
flags for the property specified |
Returns
anewly created parameter specification.
（5） g_param_spec_uint ()
链接如下：
g_param_spec_uint (const gchar *name,
const gchar *nick,
const gchar *blurb,
guint minimum,
guint maximum,
guint default_value,
GParamFlags flags);
Createsa new GParamSpecUIntinstance specifying a G_TYPE_UINT property.
See g_param_spec_internal() for details on property names.
Parameters
| name |
canonical name of the property specified |
|
| nick |
nick name for the property specified |
|
| blurb |
description of the property specified |
|
| minimum |
minimum value for the property specified |
|
| maximum |
maximum value for the property specified |
|
| default_value |
default value for the property specified |
|
| flags |
flags for the property specified |
Returns
anewly created parameter specification.
（6） g_object_class_install_property()
链接如下：
void
g_object_class_install_property (GObjectClass *oclass,
guint property_id,
GParamSpec *pspec);
Installsa new property.
Allproperties should be installed during the class initializer. It is possible toinstall properties after that, but doing so is not recommend, and specifically,is not guaranteed to be thread-safe vs. use of properties on the same type onother threads.
Notethat it is possible to redefine a property in a derived class, by installing aproperty with the same name. This can be useful at times, e.g. to change therange of allowed values or the default value.
Parameters
| oclass |
||
| property_id |
the id for the new property |
|
| pspec |
the GParamSpec for the new property |
（7） g_value_set_string ()
void
g_value_set_string (GValue *value,
const gchar *v_string);
Setthe contents of a G_TYPE_STRING GValue to v_string .
Parameters
| value |
a valid GValue of type G_TYPE_STRING |
|
| v_string |
caller-owned string to be duplicated for the GValue. |
[allow-none] |
（8） g_value_set_boolean ()
void
g_value_set_boolean (GValue *value,
gboolean v_boolean);
Setthe contents of a G_TYPE_BOOLEAN GValue to v_boolean .
Parameters
| value |
a valid GValue of type G_TYPE_BOOLEAN |
|
| v_boolean |
boolean value to be set |
（9） g_value_set_uint ()
void
g_value_set_uint (GValue *value,
guint v_uint);
Setthe contents of a G_TYPE_UINT GValue to v_uint .
Parameters
| value |
a valid GValue of type G_TYPE_UINT |
|
| v_uint |
unsigned integer value to be set |
（10） G_OBJECT_WARN_INVALID_PROPERTY_ID()
https://developer.gnome.org/gobject/stable/gobject-The-Base-Object-Type.html
#define G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, pspec)
Thismacro should be used to emit a standard warning about unexpected properties in set_property() and get_property() implementations.
Parameters
| object |
the GObject on which set_property() or get_property() was called |
|
| property_id |
the numeric id of the property |
|
| pspec |
the GParamSpec of the property |
（11） g_value_dup_string ()
gchar *
g_value_dup_string(const GValue *value);
Get acopy the contents of a G_TYPE_STRING GValue.
Parameters
| value |
a valid GValue of type G_TYPE_STRING |
Returns
anewly allocated copy of the string content of value
（12） g_value_get_boolean ()
g_value_get_boolean(const GValue *value);
Getthe contents of a G_TYPE_BOOLEAN GValue.
Parameters
| value |
a valid GValue of type G_TYPE_BOOLEAN |
Returns
booleancontents of value
（13） g_value_get_uint ()
g_value_get_uint(const GValue *value);
Get thecontents of a G_TYPE_UINT GValue.
Parameters
| value |
a valid GValue of type G_TYPE_UINT |
Returns
unsignedinteger contents of value
（二） 设置衬垫（Pad）相关的函数
（1） gst_element_class_add_pad_template()
gst_element_class_add_pad_template()
void
gst_element_class_add_pad_template (GstElementClass *klass,
GstPadTemplate *templ);
Adds apadtemplate to an element class. This is mainly used in the _class_initfunctions of classes. If a pad template with the same name as an alreadyexisting one is added the old one is replaced by the new one.
Parameters
| klass |
the GstElementClass to add the pad template to. |
|
| templ |
a GstPadTemplate to add to the element class. |
（2）gst_pad_template_new ()
gst_pad_template_new (const gchar *name_template,
GstPadDirection direction,
GstPadPresence presence,
GstCaps *caps);
Createsa new pad template with a name according to the given template and with thegiven arguments.
Parameters
| name_template |
the name template. |
|
| direction |
the GstPadDirection of the template. |
|
| presence |
the GstPadPresence of the pad. |
|
| caps |
a GstCaps set for the template. |
[transfer none] |
Returns
a new GstPadTemplate.
其中的第一个参数：
enumGstPadDirection
Thedirection of a pad.
Members
| direction is unknown. |
||
| the pad is a source pad. |
||
| the pad is a sink pad. |
其中的第二个参数：
enumGstPadPresence
Indicateswhen this pad will become available.
Members
| the pad is always available |
||
| the pad will become available depending on the media stream |
||
| the pad is only available on request with gst_element_request_pad(). |
其中的第三个参数是GstCaps，它需要设置进行性能协商，有关性能协商的链接如下：
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstCaps.html
所以，最后一个参数只能确定是一个（GstCaps *）类型的，具体的话还需要看代码。它最终需要调用GstCaps相关的函数来完成。
（三） 设置元数据（metadata）相关的函数
gst_element_class_set_static_metadata()
void
gst_element_class_set_static_metadata (GstElementClass *klass,
const gchar *longname,
const gchar *classification,
const gchar *description,
const gchar *author);
Setsthe detailed information for a GstElementClass.
Thisfunction is for use in _class_init functions only.
Sameas gst_element_class_set_metadata(), but longname , classification , description , and author must be static strings or inlined strings,as they will not be copied. (GStreamer plugins will be made resident onceloaded, so this function can be used even from dynamically loaded plugins.)
Parameters
| klass |
class to set metadata for |
|
| longname |
The long English name of the element. E.g. "File Sink" |
|
| classification |
String describing the type of element, as an unordered list separated with slashes ('/'). See draft-klass.txt of the design docs for more details and common types. E.g: "Sink/File" |
|
| description |
Sentence describing the purpose of the element. E.g: "Write stream to a file" |
|
| author |
Name and contact details of the author(s). Use \n to separate multiple author metadata. E.g: "Joe Bloggs <joe.blogs at foo.com>" |
（四） GST_DEBUG_FUNCPTR
GST_DEBUG_FUNCPTR()
#define GST_DEBUG_FUNCPTR(ptr)
Registera pointer to a function with its name, so it can later be used by GST_DEBUG_FUNCPTR_NAME().
Parameters
| ptr |
pointer to the function to register |
Returns
thevalue passed to ptr .
GST_DEBUG_FUNCPTR_NAME()
#define GST_DEBUG_FUNCPTR_NAME(ptr)
Retrievesthe name of the function, if it was previously registered with GST_DEBUG_FUNCPTR(). If not, it returns a description of thepointer.
Thismacro returns a constant string which must not be modified or freed by thecaller.
Parameters
| ptr |
address of the function of which to look up the name |
（五） GstBaseSrcClass结构体和其中的相关方法
Typesand Values
struct GstBaseSrc
structGstBaseSrc;
Theopaque GstBaseSrc data structure.
struct GstBaseSrcClass
struct GstBaseSrcClass {
GstElementClassparent_class;
/* virtual methodsfor subclasses */
/* get caps fromsubclass */
GstCaps* (*get_caps) (GstBaseSrc *src, GstCaps *filter);
/* decide on caps*/
gboolean (*negotiate) (GstBaseSrc *src);
/* called if, innegotiation, caps need fixating */
GstCaps * (*fixate) (GstBaseSrc *src, GstCaps *caps);
/* notify thesubclass of new caps */
gboolean (*set_caps) (GstBaseSrc *src, GstCaps *caps);
/* setup allocationquery */
gboolean (*decide_allocation) (GstBaseSrc *src, GstQuery *query);
/* start and stopprocessing, ideal for opening/closing the resource */
gboolean (*start) (GstBaseSrc *src);
gboolean (*stop) (GstBaseSrc *src);
/* given a buffer,return start and stop time when it should be pushed
* out. The baseclass will sync on the clock using these times. */
void (*get_times) (GstBaseSrc *src, GstBuffer *buffer,
GstClockTime*start, GstClockTime *end);
/* get the totalsize of the resource in the format set by
*gst_base_src_set_format() */
gboolean (*get_size) (GstBaseSrc *src, guint64 *size);
/* check if theresource is seekable */
gboolean (*is_seekable) (GstBaseSrc *src);
/* Prepare thesegment on which to perform do_seek(), converting to the
* current basesrcformat. */
gboolean (*prepare_seek_segment) (GstBaseSrc *src,GstEvent *seek,
GstSegment *segment);
/* notifysubclasses of a seek */
gboolean (*do_seek) (GstBaseSrc *src, GstSegment *segment);
/* unlock anypending access to the resource. subclasses should unlock
* any functionASAP. */
gboolean (*unlock) (GstBaseSrc *src);
/* Clear anypending unlock request, as we succeeded in unlocking */
gboolean (*unlock_stop) (GstBaseSrc *src);
/* notify subclassesof a query */
gboolean (*query) (GstBaseSrc *src, GstQuery *query);
/* notifysubclasses of an event */
gboolean (*event) (GstBaseSrc *src, GstEvent *event);
/* ask the subclassto create a buffer with offset and size, the default
* implementationwill call alloc and fill. */
GstFlowReturn(*create) (GstBaseSrc *src, guint64offset, guint size,
GstBuffer**buf);
/* ask the subclassto allocate an output buffer. The default implementation
* will use thenegotiated allocator. */
GstFlowReturn(*alloc) (GstBaseSrc *src, guint64offset, guint size,
GstBuffer**buf);
/* ask the subclassto fill the buffer with data from offset and size */
GstFlowReturn(*fill) (GstBaseSrc *src, guint64offset, guint size,
GstBuffer*buf);
};
Subclassescan override any of the available virtual methods or not, as needed. At theminimum, the create method should be overridden to producebuffers.
Members
| Called to get the caps to report |
||
| Negotiated the caps with the peer. |
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| Called during negotiation if caps need fixating. Implement instead of setting a fixate function on the source pad. |
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| Notify subclass of changed output caps |
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| configure the allocation query |
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| Start processing. Subclasses should open resources and prepare to produce data. Implementation should call gst_base_src_start_complete() when the operation completes, either from the current thread or any other thread that finishes the start operation asynchronously. |
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| Stop processing. Subclasses should use this to close resources. |
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| Given a buffer, return the start and stop time when it should be pushed out. The base class will sync on the clock using these times. |
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| Return the total size of the resource, in the format set by gst_base_src_set_format(). |
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| Check if the source can seek |
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| Prepare the GstSegment that will be passed to the GstBaseSrcClass.do_seek() vmethod for executing a seek request. Sub-classes should override this if they support seeking in formats other than the configured native format. By default, it tries to convert the seek arguments to the configured native format and prepare a segment in that format. |
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| Perform seeking on the resource to the indicated segment. |
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| Unlock any pending access to the resource. Subclasses should unblock any blocked function ASAP. In particular, any create() function in progress should be unblocked and should return GST_FLOW_FLUSHING. Any future GstBaseSrcClass.create() function call should also return GST_FLOW_FLUSHING until the GstBaseSrcClass.unlock_stop() function has been called. |
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| Clear the previous unlock request. Subclasses should clear any state they set during GstBaseSrcClass.unlock(), such as clearing command queues. |
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| Handle a requested query. |
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| Override this to implement custom event handling. |
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| Ask the subclass to create a buffer with offset and size. When the subclass returns GST_FLOW_OK, it MUST return a buffer of the requested size unless fewer bytes are available because an EOS condition is near. No buffer should be returned when the return value is different from GST_FLOW_OK. A return value of GST_FLOW_EOS signifies that the end of stream is reached. The default implementation will call GstBaseSrcClass.alloc() and then call GstBaseSrcClass.fill(). |
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| Ask the subclass to allocate a buffer with for offset and size. The default implementation will create a new buffer from the negotiated allocator. |
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| Ask the subclass to fill the buffer with data for offset and size. The passed buffer is guaranteed to hold the requested amount of bytes. |
enum GstBaseSrcFlags
The GstElement flags that a basesrc element may have.
Members
| has source is starting |
||
| has source been started |
||
| offset to define more flags |
（5.1） g_slice_alloc函数
g_slice_alloc(gsize block_size);
Allocatesa block of memory from the slice allocator. The block adress handed out can beexpected to be aligned to at least 1 * sizeof (void*), though in general slicesare 2 * sizeof (void*) bytes aligned, if a malloc() fallback implementation is used instead,the alignment may be reduced in a libc dependent fashion. Note that theunderlying slice allocation mechanism can be changed with the G_SLICE=always-malloc environmentvariable.
Parameters
| block_size |
the number of bytes to allocate |
Returns
apointer to the allocated memory block, which will be NULL if and only if mem_size is 0
Since:2.10
（5.3）gst_pad_get_pad_template_caps函数
GstCaps *
gst_pad_get_pad_template_caps(GstPad *pad);
Getsthe capabilities for pad 's template.
Parameters
| pad |
a GstPad to get the template capabilities from. |
Returns
the GstCaps of this pad template. Unref after usage.
gst_caps_new_empty ()
GstCaps *
gst_caps_new_empty(void);
Createsa new GstCaps that is empty. That is, the returned GstCaps contains no media formats. The GstCaps is guaranteed to be writable. Caller isresponsible for unreffing the returned caps.
Returns
thenew GstCaps.
gst_structure_set ()
void
gst_structure_set (GstStructure *structure,
const gchar *fieldname,
...);
Parsesthe variable arguments and sets fields accordingly. Fields that weren't alreadypart of the structure are added as needed. Variable arguments should be in theform field name, field type (as a GType), value(s). The last variable argumentshould be NULL.
Parameters
| structure |
||
| fieldname |
the name of the field to set |
|
| ... |
variable arguments |
gst_caps_append_structure ()
void
gst_caps_append_structure (GstCaps *caps,
GstStructure *structure);
Appendsstructure 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. |
gst_caps_simplify ()
GstCaps *
gst_caps_simplify(GstCaps *caps);
Convertsthe given caps into a representation that represents thesame set of formats, but in a simpler form. Component structures that areidentical are merged. Component structures that have values that can be mergedare also merged.
Thisfunction takes ownership of caps and will call gst_caps_make_writable() on it if necessary, so you must not use caps afterwards unless you keep an additionalreference to it with gst_caps_ref().
Thismethod does not preserve the original order of caps .
Parameters
| caps |
a GstCaps to simplify. |
[transfer full] |
Returns
Thesimplified caps.
gst_caps_ref ()
GstCaps *
gst_caps_ref(GstCaps *caps);
Add areference to a GstCaps object.
Fromthis point on, until the caller calls gst_caps_unref() or gst_caps_make_writable(), it is guaranteed that the caps objectwill not change. This means its structures won't change, etc. To use a GstCaps object, you must always have a refcount onit -- either the one made implicitly by e.g. gst_caps_new_simple(), or via taking one explicitly with thisfunction.
Parameters
| caps |
the GstCaps to reference |
Returns
thesame GstCaps object.
gst_caps_intersect_full()
GstCaps *
gst_caps_intersect_full (GstCaps *caps1,
GstCaps *caps2,
GstCapsIntersectMode mode);
Createsa new GstCaps that contains all the formats that arecommon to both caps1 and caps2 , the order is defined by the GstCapsIntersectModeused.
Parameters
| caps1 |
a GstCaps to intersect |
|
| caps2 |
a GstCaps to intersect |
|
| mode |
The intersection algorithm/mode to use |
Returns
thenew GstCaps.
enum GstCapsIntersectMode
Modesof caps intersection
GST_CAPS_INTERSECT_ZIG_ZAG tries to preserve overall order of bothcaps 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 |
Usedwhen there is no explicit precedence of one caps over the other. e.g. tee'ssink pad getcaps function, it will probe its src pad peers' for their caps andintersect them with this mode.
GST_CAPS_INTERSECT_FIRST is useful when an element wants topreserve another element's caps priority order when intersecting with its owncaps. Example: If caps1 is [A, B, C] and caps2 is [E, B, D, A], the resultwould be [A, B], maintaining the first caps priority on the intersection.
Members
| Zig-zags over both caps. |
||
| Keeps the first caps order. |
（5.5）
struct GstVideoInfo
struct GstVideoInfo {
constGstVideoFormatInfo *finfo;
GstVideoInterlaceMode interlace_mode;
GstVideoFlags flags;
gint width;
gint height;
gsize size;
gint views;
GstVideoChromaSite chroma_site;
GstVideoColorimetry colorimetry;
gint par_n;
gint par_d;
gint fps_n;
gint fps_d;
gsize offset[GST_VIDEO_MAX_PLANES];
gint stride[GST_VIDEO_MAX_PLANES];
/* Union preservespadded struct size for backwards compat
* Consumer codeshould use the accessor macros for fields */
union {
struct {
GstVideoMultiviewMode multiview_mode;
GstVideoMultiviewFlags multiview_flags;
} abi;
};
Informationdescribing image properties. This information can be filled in from GstCapswith gst_video_info_from_caps(). The information is also used to store thespecific video info when mapping a video frame with gst_video_frame_map().
Usethe provided macros to access the info in this structure.
Members
| const GstVideoFormatInfo *finfo; |
the format info of the video |
|
| GstVideoInterlaceMode interlace_mode; |
the interlace mode |
|
| GstVideoFlags flags; |
additional video flags |
|
| gint width; |
the width of the video |
|
| gint height; |
the height of the video |
|
| gsize size; |
the default size of one frame |
|
| gint views; |
the number of views for multiview video |
|
| GstVideoChromaSite chroma_site; |
||
| GstVideoColorimetry colorimetry; |
the colorimetry info |
|
| gint par_n; |
the pixel-aspect-ratio numerator |
|
| gint par_d; |
the pixel-aspect-ratio demnominator |
|
| gint fps_n; |
the framerate numerator |
|
| gint fps_d; |
the framerate demnominator |
|
| gsize offset[GST_VIDEO_MAX_PLANES]; |
offsets of the planes |
|
| gint stride[GST_VIDEO_MAX_PLANES]; |
strides of the planes |
gst_video_info_from_caps ()
gst_video_info_from_caps (GstVideoInfo *info,
const GstCaps *caps);
Parse caps and update info .
Parameters
| info |
||
| caps |
a GstCaps |
Returns
TRUEif caps could be parsed
GST_VIDEO_FRAME_WIDTH()
#defineGST_VIDEO_FRAME_WIDTH(f) (GST_VIDEO_INFO_WIDTH(&(f)->info))
GST_VIDEO_FRAME_HEIGHT()
#defineGST_VIDEO_FRAME_HEIGHT(f) (GST_VIDEO_INFO_HEIGHT(&(f)->info))
GST_VIDEO_INFO_FPS_N()
#defineGST_VIDEO_INFO_FPS_N(i) ((i)->fps_n)
GST_VIDEO_INFO_FPS_D()
#defineGST_VIDEO_INFO_FPS_D(i) ((i)->fps_d)
gst_caps_copy ()
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstCaps.html
GstCaps *
gst_caps_copy(const GstCaps *caps);
Createsa 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.
Notethat 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 areference to the data, you should use gst_caps_ref().
Whenyou are finished with the caps, call gst_caps_unref() on it.
Parameters
| caps |
a GstCaps. |
Returns
thenew GstCaps
gst_caps_is_equal ()
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstCaps.html
gst_caps_is_equal (const GstCaps *caps1,
const GstCaps *caps2);
Checksif the given caps represent the same set of caps.
Parameters
| caps1 |
a GstCaps |
|
| caps2 |
another GstCaps |
Returns
TRUE if both caps are equal.
（5.6）
gst_query_set_latency ()
void
gst_query_set_latency (GstQuery *query,
gboolean live,
GstClockTime min_latency,
GstClockTime max_latency);
Answera latency query by setting the requested values in the given format.
Parameters
| query |
a GstQuery |
|
| live |
if there is a live element upstream |
|
| min_latency |
the minimal latency of the upstream elements |
|
| max_latency |
the maximal latency of the upstream elements |
（5.7）
gst_query_parse_allocation ()
void
gst_query_parse_allocation (GstQuery *query,
GstCaps **caps,
gboolean *need_pool);
Parsean allocation query, writing the requested caps in caps and whether a pool is needed in need_pool , if the respective parameters are non-NULL.
Parameters
| query |
a GstQuery |
|
| caps |
The GstCaps. |
[out][transfer none][allow-none] |
| need_pool |
Whether a GstBufferPool is needed. |
[out][allow-none] |
gst_video_info_init ()
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-libs/html/gst-plugins-base-libs-gstvideo.html#gst-video-info-init
void
gst_video_info_init(GstVideoInfo *info);
Initializeinfo with default values.
Parameters
| info |
gst_video_info_from_caps ()
gst_video_info_from_caps (GstVideoInfo *info,
const GstCaps *caps);
Parse caps and update info .
Parameters
| info |
||
| caps |
a GstCaps |
Returns
TRUEif caps could be parsed
gst_query_get_n_allocation_pools ()
gst_query_get_n_allocation_pools(GstQuery *query);
Retrievethe number of values currently stored in the pool array of the query'sstructure.
Parameters
| query |
a GST_QUERY_ALLOCATION type query GstQuery |
Returns
thepool array size as a guint.
gst_query_set_nth_allocation_pool ()
void
gst_query_set_nth_allocation_pool (GstQuery *query,
guint index,
GstBufferPool *pool,
guint size,
guint min_buffers,
guint max_buffers);
Setthe pool parameters in query .
Parameters
| index |
index to modify |
|
| query |
A valid GstQuery of type GST_QUERY_ALLOCATION. |
|
| pool |
the GstBufferPool. |
[transfer none][allow-none] |
| size |
the size |
|
| min_buffers |
the min buffers |
|
| max_buffers |
the max buffers |
gst_query_add_allocation_pool ()
void
gst_query_add_allocation_pool (GstQuery *query,
GstBufferPool *pool,
guint size,
guint min_buffers,
guint max_buffers);
Setthe pool parameters in query.
Parameters
| query |
A valid GstQuery of type GST_QUERY_ALLOCATION. |
|
| pool |
the GstBufferPool. |
[transfer none][allow-none] |
| size |
the size |
|
| min_buffers |
the min buffers |
|
| max_buffers |
the max buffers |
gst_query_get_n_allocation_params ()
gst_query_get_n_allocation_params(GstQuery *query);
Retrievethe number of values currently stored in the allocator params array of thequery's structure.
If nomemory allocator is specified, the downstream element can handle the defaultmemory allocator. The first memory allocator in the query should be generic andallow mapping to system memory, all following allocators should be ordered bypreference with the preferred one first.
Parameters
| query |
a GST_QUERY_ALLOCATION type query GstQuery |
Returns
theallocator array size as a guint.
gst_query_parse_nth_allocation_param ()
void
gst_query_parse_nth_allocation_param (GstQuery *query,
guint index,
GstAllocator **allocator,
GstAllocationParams *params);
Parsean available query and get the allocator and its params at index of the allocator array.
Parameters
| query |
a GST_QUERY_ALLOCATION type query GstQuery |
|
| index |
position in the allocator array to read |
|
| allocator |
variable to hold the result. |
[out][transfer full][allow-none] |
| params |
parameters for the allocator. |
gst_allocation_params_init ()
void
gst_allocation_params_init(GstAllocationParams *params);
Initializeparams to its default values
Parameters
| params |
gst_query_parse_nth_allocation_pool ()
void
gst_query_parse_nth_allocation_pool (GstQuery *query,
guint index,
GstBufferPool **pool,
guint *size,
guint *min_buffers,
guint *max_buffers);
Getthe pool parameters in query .
Unref pool with gst_object_unref() when it's not needed any more.
Parameters
| query |
A valid GstQuery of type GST_QUERY_ALLOCATION. |
|
| index |
index to parse |
|
| pool |
the GstBufferPool. |
[out][allow-none][transfer full] |
| size |
the size. |
[out][allow-none] |
| min_buffers |
the min buffers. |
[out][allow-none] |
| max_buffers |
the max buffers. |
[out][allow-none] |
gst_buffer_pool_new ()
gst_buffer_pool_new(void);
Createsa new GstBufferPool instance.
Returns
a new GstBufferPool instance.
gst_video_buffer_pool_new ()
gst_video_buffer_pool_new(void);
Createa new bufferpool that can allocate video frames. This bufferpool supports allthe video bufferpool options.
Returns
a new GstBufferPool to allocate video frames.
gst_buffer_pool_get_config ()
gst_buffer_pool_get_config(GstBufferPool *pool);
Get acopy of the current configuration of the pool. This configuration can either bemodified and used for the gst_buffer_pool_set_config() call or it must be freed after usage.
Parameters
| pool |
Returns
a copyof the current configuration of pool . use gst_structure_free() after usage or gst_buffer_pool_set_config().
gst_buffer_pool_config_set_params ()
void
gst_buffer_pool_config_set_params (GstStructure *config,
GstCaps *caps,
guint size,
guint min_buffers,
guint max_buffers);
Configureconfig with the given parameters.
Parameters
| config |
a GstBufferPool configuration |
|
| caps |
caps for the buffers |
|
| size |
the size of each buffer, not including prefix and padding |
|
| min_buffers |
the minimum amount of buffers to allocate. |
|
| max_buffers |
the maximum amount of buffers to allocate or 0 for unlimited. |
gst_buffer_pool_config_set_allocator ()
void
gst_buffer_pool_config_set_allocator (GstStructure *config,
GstAllocator *allocator,
const GstAllocationParams *params);
Setthe allocator and params on config .
One ofallocator and params can be NULL, but not both. When allocator is NULL, the default allocator of the pool willuse the values in param to perform its allocation. When param is NULL, the pool will use the provided allocator with its default GstAllocationParams.
A callto gst_buffer_pool_set_config() can update the allocator and params withthe values that it is able to do. Some pools are, for example, not able tooperate with different allocators or cannot allocate with the values specifiedin params . Use gst_buffer_pool_get_config() to get the currently used values.
Parameters
| config |
a GstBufferPool configuration |
|
| allocator |
a GstAllocator. |
[allow-none] |
| params |
[allow-none] |
gst_buffer_pool_set_config ()
gst_buffer_pool_set_config (GstBufferPool *pool,
GstStructure *config);
Setthe configuration of the pool. If the pool is already configured, and the configurationhaven't change, this function will return TRUE. If the pool is active, this method willreturn FALSE and active configuration will remain.Buffers allocated form this pool must be returned or else this function will donothing and return FALSE.
config is a GstStructure that contains the configuration parametersfor the pool. A default and mandatory set of parameters can be configured with gst_buffer_pool_config_set_params(), gst_buffer_pool_config_set_allocator() and gst_buffer_pool_config_add_option().
If theparameters in config can not be set exactly, this functionreturns FALSE and will try to update as much state aspossible. The new state can then be retrieved and refined with gst_buffer_pool_get_config().
Thisfunction takes ownership of config .
Parameters
| pool |
||
| config |
a GstStructure. |
[transfer full] |
Returns
TRUE when the configuration could be set.
（5.8.1）
gst_base_src_get_buffer_pool ()
gst_base_src_get_buffer_pool(GstBaseSrc *src);
Parameters
| src |
Returns
theinstance of the GstBufferPool used by the src; unref it after usage.
struct GstVideoAlignment
struct GstVideoAlignment {
guint padding_top;
guintpadding_bottom;
guint padding_left;
guintpadding_right;
guintstride_align[GST_VIDEO_MAX_PLANES];
};
Extraalignment paramters for the memory of video buffers. This structure is usuallyused to configure the bufferpool if it supports the GST_BUFFER_POOL_OPTION_VIDEO_ALIGNMENT.
Members
| guint padding_top; |
extra pixels on the top |
|
| guint padding_bottom; |
extra pixels on the bottom |
|
| guint padding_left; |
extra pixels on the left side |
|
| guint padding_right; |
extra pixels on the right side |
|
| guint stride_align[GST_VIDEO_MAX_PLANES]; |
array with extra alignment requirements for the strides |
gst_buffer_pool_config_has_option ()
gst_buffer_pool_config_has_option (GstStructure *config,
const gchar *option);
Checkif config contains option .
Parameters
| config |
a GstBufferPool configuration |
|
| option |
an option |
Returns
TRUE if the options array contains option .
gst_buffer_pool_config_get_video_alignment ()
gst_buffer_pool_config_get_video_alignment
(GstStructure *config,
GstVideoAlignment *align);
Getthe video alignment from the bufferpool configuration config in in align
Parameters
| config |
||
| align |
Returns
TRUE if config could be parsed correctly.
gst_buffer_pool_config_get_params ()
gst_buffer_pool_config_get_params (GstStructure *config,
GstCaps **caps,
guint *size,
guint *min_buffers,
guint *max_buffers);
Getthe configuration values from config .
Parameters
| config |
a GstBufferPool configuration. |
[transfer none] |
| caps |
the caps of buffers. |
[out][transfer none][allow-none] |
| size |
the size of each buffer, not including prefix and padding. |
[out][allow-none] |
| min_buffers |
the minimum amount of buffers to allocate. |
[out][allow-none] |
| max_buffers |
the maximum amount of buffers to allocate or 0 for unlimited. |
[out][allow-none] |
Returns
TRUE if all parameters could be fetched.
（5.8.2）
gst_buffer_pool_acquire_buffer ()
gst_buffer_pool_acquire_buffer (GstBufferPool *pool,
GstBuffer **buffer,
GstBufferPoolAcquireParams *params);
Acquirea buffer from pool . buffer should point to a memory location that canhold a pointer to the new buffer.
params can be NULL or contain optional parameters toinfluence the allocation.
Parameters
| pool |
||
| buffer |
a location for a GstBuffer. |
[out] |
| params |
parameters. |
[transfer none][allow-none] |
Returns
a GstFlowReturn such as GST_FLOW_FLUSHING when the pool is inactive.
（5.8.5）
gst_buffer_add_video_meta ()
gst_buffer_add_video_meta (GstBuffer *buffer,
GstVideoFrameFlags flags,
GstVideoFormat format,
guint width,
guint height);
AttachesGstVideoMeta metadata to buffer with the given parameters and the defaultoffsets and strides for format and width x height .
Thisfunction calculates the default offsets and strides and then calls gst_buffer_add_video_meta_full() with them.
Parameters
| buffer |
||
| flags |
||
| format |
||
| width |
the width |
|
| height |
the height |
Returns
the GstVideoMetaon buffer .
gst_buffer_get_video_meta ()
gst_buffer_get_video_meta(GstBuffer *buffer);
Findthe GstVideoMeta on buffer with the lowest id .
Bufferscan contain multiple GstVideoMeta metadata items when dealing with multiviewbuffers.
Parameters
| buffer |
Returns
the GstVideoMeta with lowest id (usually 0) or NULL when there is no such metadata on buffer .
gst_video_info_from_caps ()
gst_video_info_from_caps (GstVideoInfo *info,
const GstCaps *caps);
Parse caps and update info .
Parameters
| info |
||
| caps |
a GstCaps |
Returns
TRUEif caps could be parsed