GstPad

GstPad — Object contained by elements that allows links to other elements

Synopsis


#include <gst/gst.h>


                    GstPad;
enum                GstPadDirection;
enum                GstPadFlags;
enum                GstPadLinkReturn;
#define             GST_PAD_LINK_FAILED                 (ret)
#define             GST_PAD_LINK_SUCCESSFUL             (ret)
enum                GstFlowReturn;
enum                GstActivateMode;

#define             gst_pad_get_name                    (pad)
GstPadDirection     gst_pad_get_direction               (GstPad *pad);
#define             gst_pad_get_parent                  (pad)
GstElement*         gst_pad_get_parent_element          (GstPad *pad);
GstPadTemplate*     gst_pad_get_pad_template            (GstPad *pad);
GstPadLinkReturn    gst_pad_link                        (GstPad *srcpad,
                                                         GstPad *sinkpad);
gboolean            gst_pad_unlink                      (GstPad *srcpad,
                                                         GstPad *sinkpad);
gboolean            gst_pad_is_linked                   (GstPad *pad);
gboolean            gst_pad_can_link                    (GstPad *srcpad,
                                                         GstPad *sinkpad);
GstCaps*            gst_pad_get_caps                    (GstPad *pad);
GstCaps*            gst_pad_get_allowed_caps            (GstPad *pad);
GstCaps*            gst_pad_get_negotiated_caps         (GstPad *pad);
const GstCaps*      gst_pad_get_pad_template_caps       (GstPad *pad);
gboolean            gst_pad_set_caps                    (GstPad *pad,
                                                         GstCaps *caps);
GstPad*             gst_pad_get_peer                    (GstPad *pad);
GstCaps*            gst_pad_peer_get_caps               (GstPad *pad);
void                gst_pad_use_fixed_caps              (GstPad *pad);
gboolean            gst_pad_is_active                   (GstPad *pad);
gboolean            gst_pad_set_blocked                 (GstPad *pad,
                                                         gboolean blocked);
gboolean            gst_pad_set_blocked_async           (GstPad *pad,
                                                         gboolean blocked,
                                                         GstPadBlockCallback callback,
                                                         gpointer user_data);
void                (*GstPadBlockCallback)              (GstPad *pad,
                                                         gboolean blocked,
                                                         gpointer user_data);
gboolean            gst_pad_is_blocked                  (GstPad *pad);
gboolean            gst_pad_is_blocking                 (GstPad *pad);
gulong              gst_pad_add_data_probe              (GstPad *pad,
                                                         GCallback handler,
                                                         gpointer data);
gulong              gst_pad_add_buffer_probe            (GstPad *pad,
                                                         GCallback handler,
                                                         gpointer data);
gulong              gst_pad_add_event_probe             (GstPad *pad,
                                                         GCallback handler,
                                                         gpointer data);
void                gst_pad_remove_data_probe           (GstPad *pad,
                                                         guint handler_id);
void                gst_pad_remove_buffer_probe         (GstPad *pad,
                                                         guint handler_id);
void                gst_pad_remove_event_probe          (GstPad *pad,
                                                         guint handler_id);

GstPad*             gst_pad_new                         (const gchar *name,
                                                         GstPadDirection direction);
GstPad*             gst_pad_new_from_template           (GstPadTemplate *templ,
                                                         const gchar *name);
GstPad*             gst_pad_new_from_static_template    (GstStaticPadTemplate *templ,
                                                         const gchar *name);
GstFlowReturn       gst_pad_alloc_buffer                (GstPad *pad,
                                                         guint64 offset,
                                                         gint size,
                                                         GstCaps *caps,
                                                         GstBuffer **buf);
GstFlowReturn       gst_pad_alloc_buffer_and_set_caps   (GstPad *pad,
                                                         guint64 offset,
                                                         gint size,
                                                         GstCaps *caps,
                                                         GstBuffer **buf);
void                gst_pad_set_bufferalloc_function    (GstPad *pad,
                                                         GstPadBufferAllocFunction bufalloc);
GstFlowReturn       (*GstPadBufferAllocFunction)        (GstPad *pad,
                                                         guint64 offset,
                                                         guint size,
                                                         GstCaps *caps,
                                                         GstBuffer **buf);
void                gst_pad_set_chain_function          (GstPad *pad,
                                                         GstPadChainFunction chain);
GstFlowReturn       (*GstPadChainFunction)              (GstPad *pad,
                                                         GstBuffer *buffer);
void                gst_pad_set_checkgetrange_function  (GstPad *pad,
                                                         GstPadCheckGetRangeFunction check);
gboolean            (*GstPadCheckGetRangeFunction)      (GstPad *pad);
GstFlowReturn       gst_pad_get_range                   (GstPad *pad,
                                                         guint64 offset,
                                                         guint size,
                                                         GstBuffer **buffer);
void                gst_pad_set_getrange_function       (GstPad *pad,
                                                         GstPadGetRangeFunction get);
GstFlowReturn       (*GstPadGetRangeFunction)           (GstPad *pad,
                                                         guint64 offset,
                                                         guint length,
                                                         GstBuffer **buffer);
void                gst_pad_set_event_function          (GstPad *pad,
                                                         GstPadEventFunction event);
gboolean            (*GstPadEventFunction)              (GstPad *pad,
                                                         GstEvent *event);
void                gst_pad_set_link_function           (GstPad *pad,
                                                         GstPadLinkFunction link);
GstPadLinkReturn    (*GstPadLinkFunction)               (GstPad *pad,
                                                         GstPad *peer);
void                gst_pad_set_unlink_function         (GstPad *pad,
                                                         GstPadUnlinkFunction unlink);
void                (*GstPadUnlinkFunction)             (GstPad *pad);
gboolean            gst_pad_accept_caps                 (GstPad *pad,
                                                         GstCaps *caps);
void                gst_pad_set_acceptcaps_function     (GstPad *pad,
                                                         GstPadAcceptCapsFunction acceptcaps);
gboolean            (*GstPadAcceptCapsFunction)         (GstPad *pad,
                                                         GstCaps *caps);
void                gst_pad_set_getcaps_function        (GstPad *pad,
                                                         GstPadGetCapsFunction getcaps);
GstCaps*            (*GstPadGetCapsFunction)            (GstPad *pad);
GstCaps*            gst_pad_proxy_getcaps               (GstPad *pad);
void                gst_pad_set_setcaps_function        (GstPad *pad,
                                                         GstPadSetCapsFunction setcaps);
gboolean            (*GstPadSetCapsFunction)            (GstPad *pad,
                                                         GstCaps *caps);
gboolean            gst_pad_proxy_setcaps               (GstPad *pad,
                                                         GstCaps *caps);
void                gst_pad_fixate_caps                 (GstPad *pad,
                                                         GstCaps *caps);
void                gst_pad_set_fixatecaps_function     (GstPad *pad,
                                                         GstPadFixateCapsFunction fixatecaps);
void                (*GstPadFixateCapsFunction)         (GstPad *pad,
                                                         GstCaps *caps);
GstCaps*            gst_pad_get_fixed_caps_func         (GstPad *pad);
gboolean            gst_pad_peer_accept_caps            (GstPad *pad,
                                                         GstCaps *caps);
void                gst_pad_set_activate_function       (GstPad *pad,
                                                         GstPadActivateFunction activate);
gboolean            (*GstPadActivateFunction)           (GstPad *pad);
void                gst_pad_set_activatepush_function   (GstPad *pad,
                                                         GstPadActivateModeFunction activatepush);
void                gst_pad_set_activatepull_function   (GstPad *pad,
                                                         GstPadActivateModeFunction activatepull);
gboolean            (*GstPadActivateModeFunction)       (GstPad *pad,
                                                         gboolean active);
GstFlowReturn       gst_pad_push                        (GstPad *pad,
                                                         GstBuffer *buffer);
gboolean            gst_pad_push_event                  (GstPad *pad,
                                                         GstEvent *event);
gboolean            gst_pad_check_pull_range            (GstPad *pad);
GstFlowReturn       gst_pad_pull_range                  (GstPad *pad,
                                                         guint64 offset,
                                                         guint size,
                                                         GstBuffer **buffer);
gboolean            gst_pad_activate_pull               (GstPad *pad,
                                                         gboolean active);
gboolean            gst_pad_activate_push               (GstPad *pad,
                                                         gboolean active);
gboolean            gst_pad_send_event                  (GstPad *pad,
                                                         GstEvent *event);
gboolean            gst_pad_event_default               (GstPad *pad,
                                                         GstEvent *event);
gboolean            gst_pad_query                       (GstPad *pad,
                                                         GstQuery *query);
gboolean            gst_pad_query_default               (GstPad *pad,
                                                         GstQuery *query);
gboolean            gst_pad_query_position              (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *cur);
gboolean            gst_pad_query_duration              (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *duration);
gboolean            gst_pad_query_convert               (GstPad *pad,
                                                         GstFormat src_format,
                                                         gint64 src_val,
                                                         GstFormat *dest_format,
                                                         gint64 *dest_val);
gboolean            gst_pad_query_peer_position         (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *cur);
gboolean            gst_pad_query_peer_duration         (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *duration);
gboolean            gst_pad_query_peer_convert          (GstPad *pad,
                                                         GstFormat src_format,
                                                         gint64 src_val,
                                                         GstFormat *dest_format,
                                                         gint64 *dest_val);
void                gst_pad_set_query_function          (GstPad *pad,
                                                         GstPadQueryFunction query);
gboolean            (*GstPadQueryFunction)              (GstPad *pad,
                                                         GstQuery *query);
void                gst_pad_set_query_type_function     (GstPad *pad,
                                                         GstPadQueryTypeFunction type_func);
const GstQueryType* (*GstPadQueryTypeFunction)          (GstPad *pad);
const GstQueryType* gst_pad_get_query_types             (GstPad *pad);
const GstQueryType* gst_pad_get_query_types_default     (GstPad *pad);
void                gst_pad_set_internal_link_function  (GstPad *pad,
                                                         GstPadIntLinkFunction intlink);
GList*              (*GstPadIntLinkFunction)            (GstPad *pad);
GList*              gst_pad_get_internal_links          (GstPad *pad);
GList*              gst_pad_get_internal_links_default  (GstPad *pad);
void                gst_pad_load_and_link               (xmlNodePtr self,
                                                         GstObject *parent);
gboolean            gst_pad_dispatcher                  (GstPad *pad,
                                                         GstPadDispatcherFunction dispatch,
                                                         gpointer data);
gboolean            (*GstPadDispatcherFunction)         (GstPad *pad,
                                                         gpointer data);
void                gst_pad_set_element_private         (GstPad *pad,
                                                         gpointer priv);
gpointer            gst_pad_get_element_private         (GstPad *pad);

GstFlowReturn       gst_pad_chain                       (GstPad *pad,
                                                         GstBuffer *buffer);
gboolean            gst_pad_start_task                  (GstPad *pad,
                                                         GstTaskFunction func,
                                                         gpointer data);
gboolean            gst_pad_pause_task                  (GstPad *pad);
gboolean            gst_pad_stop_task                   (GstPad *pad);
gboolean            gst_pad_set_active                  (GstPad *pad,
                                                         gboolean active);
#define             GST_PAD_GET_STREAM_LOCK             (pad)
#define             GST_PAD_STREAM_LOCK                 (pad)
#define             GST_PAD_STREAM_LOCK_FULL            (pad,t)
#define             GST_PAD_STREAM_TRYLOCK              (pad)
#define             GST_PAD_STREAM_UNLOCK               (pad)
#define             GST_PAD_STREAM_UNLOCK_FULL          (pad)
#define             GST_FLOW_IS_FATAL                   (ret)
#define             GST_FLOW_IS_SUCCESS                 (ret)


Object Hierarchy


  GObject
   +----GstObject
         +----GstPad
               +----GstProxyPad

Properties


  "caps"                     GstCaps               : Read
  "direction"                GstPadDirection       : Read / Write / Construct Only
  "template"                 GstPadTemplate        : Read / Write

Signals


  "have-data"                                      : Run Last / Has Details
  "linked"                                         : Run Last
  "request-link"                                   : Run Last
  "unlinked"                                       : Run Last

Description

A GstElement is linked to other elements via "pads", which are extremely light-weight generic link points. After two pads are retrieved from an element with gst_element_get_pad(), the pads can be link with gst_pad_link(). (For quick links, you can also use gst_element_link(), which will make the obvious link for you if it's straightforward.)

Pads are typically created from a GstPadTemplate with gst_pad_new_from_template().

Pads have GstCaps attached to it to describe the media type they are capable of dealing with. gst_pad_get_caps() and gst_pad_set_caps() are used to manipulate the caps of the pads. Pads created from a pad template cannot set capabilities that are incompatible with the pad template capabilities.

Pads without pad templates can be created with gst_pad_new(), which takes a direction and a name as an argument. If the name is NULL, then a guaranteed unique name will be assigned to it.

gst_pad_get_parent() will retrieve the GstElement that owns the pad.

A GstElement creating a pad will typically use the various gst_pad_set_*_function() calls to register callbacks for various events on the pads.

GstElements will use gst_pad_push() and gst_pad_pull_range() to push out or pull in a buffer.

To send a GstEvent on a pad, use gst_pad_send_event() and gst_pad_push_event().

Last reviewed on 2006-07-06 (0.10.9)

Details

GstPad

typedef struct {
  gpointer			element_private;

  GstPadTemplate		*padtemplate;

  GstPadDirection		 direction;

  /* streaming rec_lock */
  GStaticRecMutex		*stream_rec_lock;
  GstTask			*task;
  GMutex			*preroll_lock;
  GCond				*preroll_cond;

  /* block cond, mutex is from the object */
  GCond				*block_cond;
  GstPadBlockCallback		 block_callback;
  gpointer			 block_data;

  /* the pad capabilities */
  GstCaps			*caps;
  GstPadGetCapsFunction		getcapsfunc;
  GstPadSetCapsFunction		setcapsfunc;
  GstPadAcceptCapsFunction	 acceptcapsfunc;
  GstPadFixateCapsFunction	 fixatecapsfunc;

  GstPadActivateFunction	 activatefunc;
  GstPadActivateModeFunction	 activatepushfunc;
  GstPadActivateModeFunction	 activatepullfunc;

  /* pad link */
  GstPadLinkFunction		 linkfunc;
  GstPadUnlinkFunction		 unlinkfunc;
  GstPad			*peer;

  gpointer			 sched_private;

  /* data transport functions */
  GstPadChainFunction		 chainfunc;
  GstPadCheckGetRangeFunction	 checkgetrangefunc;
  GstPadGetRangeFunction	 getrangefunc;
  GstPadEventFunction		 eventfunc;

  GstActivateMode		 mode;

  /* generic query method */
  GstPadQueryTypeFunction	 querytypefunc;
  GstPadQueryFunction		 queryfunc;

  /* internal links */
  GstPadIntLinkFunction		 intlinkfunc;

  GstPadBufferAllocFunction      bufferallocfunc;

  /* whether to emit signals for have-data. counts number
   * of handlers attached. */
  gint				 do_buffer_signals;
  gint				 do_event_signals;
} GstPad;

The GstPad structure. Use the functions to update the variables.

gpointer element_private; private data owned by the parent element
GstPadTemplate *padtemplate; padtemplate for this pad
GstPadDirection direction; the direction of the pad, cannot change after creating the pad.
GStaticRecMutex *stream_rec_lock; recursive stream lock of the pad, used to protect the data used in streaming.
GstTask *task; task for this pad if the pad is actively driving dataflow.
GMutex *preroll_lock; lock used when prerolling
GCond *preroll_cond; conf to signal preroll
GCond *block_cond; conditional to signal pad block
GstPadBlockCallback block_callback; callback for the pad block if any
gpointer block_data; user data for block_callback
GstCaps *caps; the current caps of the pad
GstPadGetCapsFunction getcapsfunc; function to get caps of the pad
GstPadSetCapsFunction setcapsfunc; function to set caps on the pad
GstPadAcceptCapsFunction acceptcapsfunc; function to check if pad can accept caps
GstPadFixateCapsFunction fixatecapsfunc; function to fixate caps
GstPadActivateFunction activatefunc; pad activation function
GstPadActivateModeFunction activatepushfunc; function to activate/deactivate pad in push mode
GstPadActivateModeFunction activatepullfunc; function to activate/deactivate pad in pull mode
GstPadLinkFunction linkfunc; function called when pad is linked
GstPadUnlinkFunction unlinkfunc; function called when pad is unlinked
GstPad *peer; the pad this pad is linked to
gpointer sched_private; private storage for the scheduler
GstPadChainFunction chainfunc; function to chain data to pad
GstPadCheckGetRangeFunction checkgetrangefunc; function to check if pad can operate in pull mode
GstPadGetRangeFunction getrangefunc; function to get a range of data from a pad
GstPadEventFunction eventfunc; function to send an event to a pad
GstActivateMode mode; current activation mode of the pad
GstPadQueryTypeFunction querytypefunc; get list of supported queries
GstPadQueryFunction queryfunc; perform a query on the pad
GstPadIntLinkFunction intlinkfunc; get the internal links of this pad
GstPadBufferAllocFunction bufferallocfunc; function to allocate a buffer for this pad
gint do_buffer_signals; counter counting installed buffer signals
gint do_event_signals; counter counting installed event signals

enum GstPadDirection

typedef enum {
  GST_PAD_UNKNOWN,
  GST_PAD_SRC,
  GST_PAD_SINK
} GstPadDirection;

The direction of a pad.

GST_PAD_UNKNOWN direction is unknown.
GST_PAD_SRC the pad is a source pad.
GST_PAD_SINK the pad is a sink pad.

enum GstPadFlags

typedef enum {
  GST_PAD_BLOCKED       = (GST_OBJECT_FLAG_LAST << 0),
  GST_PAD_FLUSHING      = (GST_OBJECT_FLAG_LAST << 1),
  GST_PAD_IN_GETCAPS    = (GST_OBJECT_FLAG_LAST << 2),
  GST_PAD_IN_SETCAPS    = (GST_OBJECT_FLAG_LAST << 3),
  GST_PAD_BLOCKING	= (GST_OBJECT_FLAG_LAST << 4),
  /* padding */
  GST_PAD_FLAG_LAST     = (GST_OBJECT_FLAG_LAST << 8)
} GstPadFlags;

Pad state flags

GST_PAD_BLOCKED is dataflow on a pad blocked
GST_PAD_FLUSHING is pad refusing buffers
GST_PAD_IN_GETCAPS GstPadGetCapsFunction() is running now
GST_PAD_IN_SETCAPS GstPadSetCapsFunction() is running now
GST_PAD_BLOCKING is pad currently blocking on a buffer or event
GST_PAD_FLAG_LAST offset to define more flags

enum GstPadLinkReturn

typedef enum {
  GST_PAD_LINK_OK               =  0,
  GST_PAD_LINK_WRONG_HIERARCHY  = -1,
  GST_PAD_LINK_WAS_LINKED       = -2,
  GST_PAD_LINK_WRONG_DIRECTION  = -3,
  GST_PAD_LINK_NOFORMAT         = -4,
  GST_PAD_LINK_NOSCHED          = -5,
  GST_PAD_LINK_REFUSED          = -6
} GstPadLinkReturn;

Result values from gst_pad_link and friends.

GST_PAD_LINK_OK link succeeded
GST_PAD_LINK_WRONG_HIERARCHY pads have no common grandparent
GST_PAD_LINK_WAS_LINKED pad was already linked
GST_PAD_LINK_WRONG_DIRECTION pads have wrong direction
GST_PAD_LINK_NOFORMAT pads do not have common format
GST_PAD_LINK_NOSCHED pads cannot cooperate in scheduling
GST_PAD_LINK_REFUSED refused for some reason

GST_PAD_LINK_FAILED()

#define GST_PAD_LINK_FAILED(ret) ((ret) < GST_PAD_LINK_OK)

Macro to test if the given GstPadLinkReturn value indicates a failed link step.

ret : the GstPadLinkReturn value

GST_PAD_LINK_SUCCESSFUL()

#define GST_PAD_LINK_SUCCESSFUL(ret) ((ret) >= GST_PAD_LINK_OK)

Macro to test if the given GstPadLinkReturn value indicates a successful link step.

ret : the GstPadLinkReturn value

enum GstFlowReturn

typedef enum {
  /* custom success starts here */
  GST_FLOW_CUSTOM_SUCCESS = 100,

  /* core predefined */
  GST_FLOW_RESEND	  =  1,
  GST_FLOW_OK		  =  0,
  /* expected failures */
  GST_FLOW_NOT_LINKED     = -1,
  GST_FLOW_WRONG_STATE    = -2,
  /* error cases */
  GST_FLOW_UNEXPECTED     = -3,
  GST_FLOW_NOT_NEGOTIATED = -4,
  GST_FLOW_ERROR	  = -5,
  GST_FLOW_NOT_SUPPORTED  = -6,

  /* custom error starts here */
  GST_FLOW_CUSTOM_ERROR   = -100
} GstFlowReturn;

The result of passing data to a pad.

Note that the custom return values should not be exposed outside of the element scope and are available since 0.10.7.

GST_FLOW_CUSTOM_SUCCESS Elements can use values starting from this to define custom success codes. Since 0.10.7.
GST_FLOW_RESEND Resend buffer, possibly with new caps (not send yet).
GST_FLOW_OK Data passing was ok.
GST_FLOW_NOT_LINKED Pad is not linked.
GST_FLOW_WRONG_STATE Pad is in wrong state.
GST_FLOW_UNEXPECTED Did not expect anything, like after EOS.
GST_FLOW_NOT_NEGOTIATED Pad is not negotiated.
GST_FLOW_ERROR Some (fatal) error occured. Element generating this error should post an error message with more details.
GST_FLOW_NOT_SUPPORTED This operation is not supported.
GST_FLOW_CUSTOM_ERROR Elements can use values starting from this to define custom error codes. Since 0.10.7.

enum GstActivateMode

typedef enum {
  GST_ACTIVATE_NONE,
  GST_ACTIVATE_PUSH,
  GST_ACTIVATE_PULL
} GstActivateMode;

The status of a GstPad. After activating a pad, which usually happens when the parent element goes from READY to PAUSED, the GstActivateMode defines if the pad operates in push or pull mode.

GST_ACTIVATE_NONE Pad will not handle dataflow
GST_ACTIVATE_PUSH Pad handles dataflow in downstream push mode
GST_ACTIVATE_PULL Pad handles dataflow in upstream pull mode

gst_pad_get_name()

#define gst_pad_get_name(pad) gst_object_get_name (GST_OBJECT_CAST (pad))

Get a copy of the name of the pad. g_free() after usage.

MT safe.

pad : the pad to get the name from

gst_pad_get_direction ()

GstPadDirection     gst_pad_get_direction               (GstPad *pad);

Gets the direction of the pad. The direction of the pad is decided at construction time so this function does not take the LOCK.

pad : a GstPad to get the direction of.
Returns : the GstPadDirection of the pad. MT safe.

gst_pad_get_parent()

#define gst_pad_get_parent(pad) gst_object_get_parent (GST_OBJECT_CAST (pad))

Get the parent of pad. This function increases the refcount of the parent object so you should gst_object_unref() it after usage. Can return NULL if the pad did not have a parent.

MT safe.

pad : the pad to get the parent of

gst_pad_get_parent_element ()

GstElement*         gst_pad_get_parent_element          (GstPad *pad);

Gets the parent of pad, cast to a GstElement. If a pad has no parent or its parent is not an element, return NULL.

pad : a pad
Returns : The parent of the pad. The caller has a reference on the parent, so unref when you're finished with it. MT safe.

gst_pad_get_pad_template ()

GstPadTemplate*     gst_pad_get_pad_template            (GstPad *pad);

Gets the template for pad.

pad : a GstPad.
Returns : the GstPadTemplate from which this pad was instantiated, or NULL if this pad has no template. FIXME: currently returns an unrefcounted padtemplate.

gst_pad_link ()

GstPadLinkReturn    gst_pad_link                        (GstPad *srcpad,
                                                         GstPad *sinkpad);

Links the source pad and the sink pad.

srcpad : the source GstPad to link.
sinkpad : the sink GstPad to link.
Returns : A result code indicating if the connection worked or what went wrong. MT Safe.

gst_pad_unlink ()

gboolean            gst_pad_unlink                      (GstPad *srcpad,
                                                         GstPad *sinkpad);

Unlinks the source pad from the sink pad. Will emit the "unlinked" signal on both pads.

srcpad : the source GstPad to unlink.
sinkpad : the sink GstPad to unlink.
Returns : TRUE if the pads were unlinked. This function returns FALSE if the pads were not linked together. MT safe.

gst_pad_is_linked ()

gboolean            gst_pad_is_linked                   (GstPad *pad);

Checks if a pad is linked to another pad or not.

pad : pad to check
Returns : TRUE if the pad is linked, FALSE otherwise. MT safe.

gst_pad_can_link ()

gboolean            gst_pad_can_link                    (GstPad *srcpad,
                                                         GstPad *sinkpad);

Checks if the source pad and the sink pad can be linked. Both srcpad and sinkpad must be unlinked.

srcpad : the source GstPad to link.
sinkpad : the sink GstPad to link.
Returns : TRUE if the pads can be linked, FALSE otherwise.

gst_pad_get_caps ()

GstCaps*            gst_pad_get_caps                    (GstPad *pad);

Gets the capabilities this pad can produce or consume. Note that this method doesn't necessarily return the caps set by gst_pad_set_caps() - use GST_PAD_CAPS for that instead. gst_pad_get_caps returns all possible caps a pad can operate with, using the pad's get_caps function; this returns the pad template caps if not explicitly set.

pad : a GstPad to get the capabilities of.
Returns : a newly allocated copy of the GstCaps of this pad. MT safe.

gst_pad_get_allowed_caps ()

GstCaps*            gst_pad_get_allowed_caps            (GstPad *pad);

Gets the capabilities of the allowed media types that can flow through pad and its peer.

The allowed capabilities is calculated as the intersection of the results of calling gst_pad_get_caps() on pad and its peer. The caller owns a reference on the resulting caps.

pad : a GstPad.
Returns : the allowed GstCaps of the pad link. Unref the caps when you no longer need it. This function returns NULL when pad has no peer. MT safe.

gst_pad_get_negotiated_caps ()

GstCaps*            gst_pad_get_negotiated_caps         (GstPad *pad);

Gets the capabilities of the media type that currently flows through pad and its peer.

This function can be used on both src and sinkpads. Note that srcpads are always negotiated before sinkpads so it is possible that the negotiated caps on the srcpad do not match the negotiated caps of the peer.

pad : a GstPad.
Returns : the negotiated GstCaps of the pad link. Unref the caps when you no longer need it. This function returns NULL when the pad has no peer or is not negotiated yet. MT safe.

gst_pad_get_pad_template_caps ()

const GstCaps*      gst_pad_get_pad_template_caps       (GstPad *pad);

Gets the capabilities for pad's template.

pad : a GstPad to get the template capabilities from.
Returns : the GstCaps of this pad template. If you intend to keep a reference on the caps, make a copy (see gst_caps_copy()).

gst_pad_set_caps ()

gboolean            gst_pad_set_caps                    (GstPad *pad,
                                                         GstCaps *caps);

Sets the capabilities of this pad. The caps must be fixed. Any previous caps on the pad will be unreffed. This function refs the caps so you should unref if as soon as you don't need it anymore. It is possible to set NULL caps, which will make the pad unnegotiated again.

pad : a GstPad to set the capabilities of.
caps : a GstCaps to set.
Returns : TRUE if the caps could be set. FALSE if the caps were not fixed or bad parameters were provided to this function. MT safe.

gst_pad_get_peer ()

GstPad*             gst_pad_get_peer                    (GstPad *pad);

Gets the peer of pad. This function refs the peer pad so you need to unref it after use.

pad : a GstPad to get the peer of.
Returns : the peer GstPad. Unref after usage. MT safe.

gst_pad_peer_get_caps ()

GstCaps*            gst_pad_peer_get_caps               (GstPad *pad);

Gets the capabilities of the peer connected to this pad.

pad : a GstPad to get the peer capabilities of.
Returns : the GstCaps of the peer pad. This function returns a new caps, so use gst_caps_unref to get rid of it. this function returns NULL if there is no peer pad.

gst_pad_use_fixed_caps ()

void                gst_pad_use_fixed_caps              (GstPad *pad);

A helper function you can use that sets the gst_pad_get_fixed_caps_func as the getcaps function for the pad. This way the function will always return the negotiated caps or in case the pad is not negotiated, the padtemplate caps.

Use this function on a pad that, once _set_caps() has been called on it, cannot be renegotiated to something else.

pad : the pad to use

gst_pad_is_active ()

gboolean            gst_pad_is_active                   (GstPad *pad);

Query if a pad is active

pad : the GstPad to query
Returns : TRUE if the pad is active. MT safe.

gst_pad_set_blocked ()

gboolean            gst_pad_set_blocked                 (GstPad *pad,
                                                         gboolean blocked);

Blocks or unblocks the dataflow on a pad. This function is a shortcut for gst_pad_set_blocked_async() with a NULL callback.

pad : the GstPad to block or unblock
blocked : boolean indicating we should block or unblock
Returns : TRUE if the pad could be blocked. This function can fail if the wrong parameters were passed or the pad was already in the requested state. MT safe.

gst_pad_set_blocked_async ()

gboolean            gst_pad_set_blocked_async           (GstPad *pad,
                                                         gboolean blocked,
                                                         GstPadBlockCallback callback,
                                                         gpointer user_data);

Blocks or unblocks the dataflow on a pad. The provided callback is called when the operation succeeds; this happens right before the next attempt at pushing a buffer on the pad.

This can take a while as the pad can only become blocked when real dataflow is happening. When the pipeline is stalled, for example in PAUSED, this can take an indeterminate amount of time. You can pass NULL as the callback to make this call block. Be careful with this blocking call as it might not return for reasons stated above.

pad : the GstPad to block or unblock
blocked : boolean indicating whether the pad should be blocked or unblocked
callback : GstPadBlockCallback that will be called when the operation succeeds
user_data : user data passed to the callback
Returns : TRUE if the pad could be blocked. This function can fail if the wrong parameters were passed or the pad was already in the requested state. MT safe.

GstPadBlockCallback ()

void                (*GstPadBlockCallback)              (GstPad *pad,
                                                         gboolean blocked,
                                                         gpointer user_data);

Callback used by gst_pad_set_blocked_async(). Gets called when the blocking operation succeeds.

pad : the GstPad that is blockend or unblocked.
blocked : blocking state for the pad
user_data : the gpointer to optional user data.

gst_pad_is_blocked ()

gboolean            gst_pad_is_blocked                  (GstPad *pad);

Checks if the pad is blocked or not. This function returns the last requested state of the pad. It is not certain that the pad is actually blocking at this point (see gst_pad_is_blocking()).

pad : the GstPad to query
Returns : TRUE if the pad is blocked. MT safe.

gst_pad_is_blocking ()

gboolean            gst_pad_is_blocking                 (GstPad *pad);

Checks if the pad is blocking or not. This is a guaranteed state of whether the pad is actually blocking on a GstBuffer or a GstEvent.

pad : the GstPad to query
Returns : TRUE if the pad is blocking. MT safe.

Since 0.10.11


gst_pad_add_data_probe ()

gulong              gst_pad_add_data_probe              (GstPad *pad,
                                                         GCallback handler,
                                                         gpointer data);

Adds a "data probe" to a pad. This function will be called whenever data passes through a pad. In this case data means both events and buffers. The probe will be called with the data as an argument, meaning handler should have the same callback signature as the 'have-data' signal of GstPad. Note that the data will have a reference count greater than 1, so it will be immutable -- you must not change it.

For source pads, the probe will be called after the blocking function, if any (see gst_pad_set_blocked_async()), but before looking up the peer to chain to. For sink pads, the probe function will be called before configuring the sink with new caps, if any, and before calling the pad's chain function.

Your data probe should return TRUE to let the data continue to flow, or FALSE to drop it. Dropping data is rarely useful, but occasionally comes in handy with events.

Although probes are implemented internally by connecting handler to the have-data signal on the pad, if you want to remove a probe it is insufficient to only call g_signal_handler_disconnect on the returned handler id. To remove a probe, use the appropriate function, such as gst_pad_remove_data_probe().

pad : pad to add the data probe handler to
handler : function to call when data is passed over pad
data : data to pass along with the handler
Returns : The handler id.

gst_pad_add_buffer_probe ()

gulong              gst_pad_add_buffer_probe            (GstPad *pad,
                                                         GCallback handler,
                                                         gpointer data);

Adds a probe that will be called for all buffers passing through a pad. See gst_pad_add_data_probe() for more information.

pad : pad to add the buffer probe handler to
handler : function to call when data is passed over pad
data : data to pass along with the handler
Returns : The handler id

gst_pad_add_event_probe ()

gulong              gst_pad_add_event_probe             (GstPad *pad,
                                                         GCallback handler,
                                                         gpointer data);

Adds a probe that will be called for all events passing through a pad. See gst_pad_add_data_probe() for more information.

pad : pad to add the event probe handler to
handler : function to call when data is passed over pad
data : data to pass along with the handler
Returns : The handler id

gst_pad_remove_data_probe ()

void                gst_pad_remove_data_probe           (GstPad *pad,
                                                         guint handler_id);

Removes a data probe from pad.

pad : pad to remove the data probe handler from
handler_id : handler id returned from gst_pad_add_data_probe

gst_pad_remove_buffer_probe ()

void                gst_pad_remove_buffer_probe         (GstPad *pad,
                                                         guint handler_id);

Removes a buffer probe from pad.

pad : pad to remove the buffer probe handler from
handler_id : handler id returned from gst_pad_add_buffer_probe

gst_pad_remove_event_probe ()

void                gst_pad_remove_event_probe          (GstPad *pad,
                                                         guint handler_id);

Removes an event probe from pad.

pad : pad to remove the event probe handler from
handler_id : handler id returned from gst_pad_add_event_probe

gst_pad_new ()

GstPad*             gst_pad_new                         (const gchar *name,
                                                         GstPadDirection direction);

Creates a new pad with the given name in the given direction. If name is NULL, a guaranteed unique name (across all pads) will be assigned. This function makes a copy of the name so you can safely free the name.

name : the name of the new pad.
direction : the GstPadDirection of the pad.
Returns : a new GstPad, or NULL in case of an error. MT safe.

gst_pad_new_from_template ()

GstPad*             gst_pad_new_from_template           (GstPadTemplate *templ,
                                                         const gchar *name);

Creates a new pad with the given name from the given template. If name is NULL, a guaranteed unique name (across all pads) will be assigned. This function makes a copy of the name so you can safely free the name.

templ : the pad template to use
name : the name of the element
Returns : a new GstPad, or NULL in case of an error.

gst_pad_new_from_static_template ()

GstPad*             gst_pad_new_from_static_template    (GstStaticPadTemplate *templ,
                                                         const gchar *name);

Creates a new pad with the given name from the given static template. If name is NULL, a guaranteed unique name (across all pads) will be assigned. This function makes a copy of the name so you can safely free the name.

templ : the GstStaticPadTemplate to use
name : the name of the element
Returns : a new GstPad, or NULL in case of an error.

gst_pad_alloc_buffer ()

GstFlowReturn       gst_pad_alloc_buffer                (GstPad *pad,
                                                         guint64 offset,
                                                         gint size,
                                                         GstCaps *caps,
                                                         GstBuffer **buf);

Allocates a new, empty buffer optimized to push to pad pad. This function only works if pad is a source pad and has a peer.

A new, empty GstBuffer will be put in the buf argument. You need to check the caps of the buffer after performing this function and renegotiate to the format if needed.

pad : a source GstPad
offset : the offset of the new buffer in the stream
size : the size of the new buffer
caps : the caps of the new buffer
buf : a newly allocated buffer
Returns : a result code indicating success of the operation. Any result code other than GST_FLOW_OK is an error and buf should not be used. An error can occur if the pad is not connected or when the downstream peer elements cannot provide an acceptable buffer. MT safe.

gst_pad_alloc_buffer_and_set_caps ()

GstFlowReturn       gst_pad_alloc_buffer_and_set_caps   (GstPad *pad,
                                                         guint64 offset,
                                                         gint size,
                                                         GstCaps *caps,
                                                         GstBuffer **buf);

In addition to the function gst_pad_alloc_buffer(), this function automatically calls gst_pad_set_caps() when the caps of the newly allocated buffer are different from the pad caps.

pad : a source GstPad
offset : the offset of the new buffer in the stream
size : the size of the new buffer
caps : the caps of the new buffer
buf : a newly allocated buffer
Returns : a result code indicating success of the operation. Any result code other than GST_FLOW_OK is an error and buf should not be used. An error can occur if the pad is not connected or when the downstream peer elements cannot provide an acceptable buffer. MT safe.

gst_pad_set_bufferalloc_function ()

void                gst_pad_set_bufferalloc_function    (GstPad *pad,
                                                         GstPadBufferAllocFunction bufalloc);

Sets the given bufferalloc function for the pad. Note that the bufferalloc function can only be set on sinkpads.

pad : a sink GstPad.
bufalloc : the GstPadBufferAllocFunction to set.

GstPadBufferAllocFunction ()

GstFlowReturn       (*GstPadBufferAllocFunction)        (GstPad *pad,
                                                         guint64 offset,
                                                         guint size,
                                                         GstCaps *caps,
                                                         GstBuffer **buf);

Ask the sinkpad pad to allocate a buffer with offset, size and caps. The result will be stored in buf.

The purpose of this function is to allocate a buffer that is optimal to be processed by pad. The function is mostly overridden by elements that can provide a hardware buffer in order to avoid additional memcpy operations.

The function can return a buffer that does not have caps, in which case the upstream element requests a format change. If a format change was requested, the returned buffer will be one to hold the data of said new caps, so its size might be different from size.

When this function returns anything else than GST_FLOW_OK, the buffer allocation failed and buf does not contain valid data.

By default this function returns a new buffer of size and with caps containing purely malloced data. The buffer should be freed with gst_buffer_unref() after usage.

pad : a sink GstPad
offset : the desired offset of the buffer
size : the desired size of the buffer
caps : the desired caps of the buffer
buf : pointer to hold the allocated buffer.
Returns : GST_FLOW_OK if buf contains a valid buffer, any other return value means buf does not hold a valid buffer.

gst_pad_set_chain_function ()

void                gst_pad_set_chain_function          (GstPad *pad,
                                                         GstPadChainFunction chain);

Sets the given chain function for the pad. The chain function is called to process a GstBuffer input buffer. see GstPadChainFunction for more details.

pad : a sink GstPad.
chain : the GstPadChainFunction to set.

GstPadChainFunction ()

GstFlowReturn       (*GstPadChainFunction)              (GstPad *pad,
                                                         GstBuffer *buffer);

A function that will be called on sinkpads when chaining buffers. The function typically processes the data contained in the buffer and either consumes the data or passes it on to the internally linked pad(s).

The implementer of this function receives a refcount to buffer and should gst_buffer_unref() when the buffer is no longer needed.

When a chain function detects an error in the data stream, it must post an error on the buffer and return an appropriate GstFlowReturn value.

pad : the sink GstPad that performed the chain.
buffer : the GstBuffer that is chained, not NULL.
Returns : GST_FLOW_OK for success

gst_pad_set_checkgetrange_function ()

void                gst_pad_set_checkgetrange_function  (GstPad *pad,
                                                         GstPadCheckGetRangeFunction check);

Sets the given checkgetrange function for the pad. Implement this function on a pad if you dynamically support getrange based scheduling on the pad.

pad : a source GstPad.
check : the GstPadCheckGetRangeFunction to set.

GstPadCheckGetRangeFunction ()

gboolean            (*GstPadCheckGetRangeFunction)      (GstPad *pad);

Check if pad can be activated in pull mode.

This function will be deprecated after 0.10; use the seeking query to check if a pad can support random access.

pad : a GstPad
Returns : TRUE if the pad can operate in pull mode.

gst_pad_get_range ()

GstFlowReturn       gst_pad_get_range                   (GstPad *pad,
                                                         guint64 offset,
                                                         guint size,
                                                         GstBuffer **buffer);

When pad is flushing this function returns GST_FLOW_WRONG_STATE immediatly.

Calls the getrange function of pad, see GstPadGetRangeFunction for a description of a getrange function. If pad has no getrange function installed (see gst_pad_set_getrange_function()) this function returns GST_FLOW_NOT_SUPPORTED.

buffer's caps must either be unset or the same as what is already configured on pad. Renegotiation within a running pull-mode pipeline is not supported.

This is a lowlevel function. Usualy gst_pad_pull_range() is used.

pad : a src GstPad, returns GST_FLOW_ERROR if not.
offset : The start offset of the buffer
size : The length of the buffer
buffer : a pointer to hold the GstBuffer, returns GST_FLOW_ERROR if NULL.
Returns : a GstFlowReturn from the pad. MT safe.

gst_pad_set_getrange_function ()

void                gst_pad_set_getrange_function       (GstPad *pad,
                                                         GstPadGetRangeFunction get);

Sets the given getrange function for the pad. The getrange function is called to produce a new GstBuffer to start the processing pipeline. see GstPadGetRangeFunction for a description of the getrange function.

pad : a source GstPad.
get : the GstPadGetRangeFunction to set.

GstPadGetRangeFunction ()

GstFlowReturn       (*GstPadGetRangeFunction)           (GstPad *pad,
                                                         guint64 offset,
                                                         guint length,
                                                         GstBuffer **buffer);

This function will be called on source pads when a peer element request a buffer at the specified offset and length. If this function returns GST_FLOW_OK, the result buffer will be stored in buffer. The contents of buffer is invalid for any other return value.

This function is installed on a source pad with gst_pad_set_getrange_function() and can only be called on source pads after they are successfully activated with gst_pad_activate_pull().

offset and length are always given in byte units. offset must normally be a value between 0 and the length in bytes of the data available on pad. The length (duration in bytes) can be retrieved with a GST_QUERY_DURATION or with a GST_QUERY_SEEKING.

Any offset larger or equal than the length will make the function return GST_FLOW_UNEXPECTED, which corresponds to EOS. In this case buffer does not contain a valid buffer.

The buffer size of buffer might be smaller than length when offset is near the end of the stream.

It is allowed to call this function with a 0 length and valid offset, in which case buffer will contain a 0-sized buffer and the function returns GST_FLOW_OK.

When this function is called with a -1 offset, the sequentially next buffer of length length in the stream is returned.

When this function is called with a -1 length, a buffer with a default optimal length is returned in buffer. The length might depend on the value of offset.

pad : the src GstPad to perform the getrange on.
offset : the offset of the range
length : the length of the range
buffer : a memory location to hold the result buffer, cannot be NULL.
Returns : GST_FLOW_OK for success

gst_pad_set_event_function ()

void                gst_pad_set_event_function          (GstPad *pad,
                                                         GstPadEventFunction event);

Sets the given event handler for the pad.

pad : a GstPad of either direction.
event : the GstPadEventFunction to set.

GstPadEventFunction ()

gboolean            (*GstPadEventFunction)              (GstPad *pad,
                                                         GstEvent *event);

Function signature to handle an event for the pad.

pad : the GstPad to handle the event.
event : the GstEvent to handle.
Returns : TRUE if the pad could handle the event.

gst_pad_set_link_function ()

void                gst_pad_set_link_function           (GstPad *pad,
                                                         GstPadLinkFunction link);

Sets the given link function for the pad. It will be called when the pad is linked with another pad.

The return value GST_PAD_LINK_OK should be used when the connection can be made.

The return value GST_PAD_LINK_REFUSED should be used when the connection cannot be made for some reason.

If link is installed on a source pad, it should call the GstPadLinkFunction of the peer sink pad, if present.

pad : a GstPad.
link : the GstPadLinkFunction to set.

GstPadLinkFunction ()

GstPadLinkReturn    (*GstPadLinkFunction)               (GstPad *pad,
                                                         GstPad *peer);

Function signature to handle a new link on the pad.

pad : the GstPad that is linked.
peer : the peer GstPad of the link
Returns : the result of the link with the specified peer.

gst_pad_set_unlink_function ()

void                gst_pad_set_unlink_function         (GstPad *pad,
                                                         GstPadUnlinkFunction unlink);

Sets the given unlink function for the pad. It will be called when the pad is unlinked.

pad : a GstPad.
unlink : the GstPadUnlinkFunction to set.

GstPadUnlinkFunction ()

void                (*GstPadUnlinkFunction)             (GstPad *pad);

Function signature to handle a unlinking the pad prom its peer.

pad : the GstPad that is linked.

gst_pad_accept_caps ()

gboolean            gst_pad_accept_caps                 (GstPad *pad,
                                                         GstCaps *caps);

Check if the given pad accepts the caps.

pad : a GstPad to check
caps : a GstCaps to check on the pad
Returns : TRUE if the pad can accept the caps.

gst_pad_set_acceptcaps_function ()

void                gst_pad_set_acceptcaps_function     (GstPad *pad,
                                                         GstPadAcceptCapsFunction acceptcaps);

Sets the given acceptcaps function for the pad. The acceptcaps function will be called to check if the pad can accept the given caps. Setting the acceptcaps function to NULL restores the default behaviour of allowing any caps that matches the caps from gst_pad_get_caps.

pad : a GstPad.
acceptcaps : the GstPadAcceptCapsFunction to set.

GstPadAcceptCapsFunction ()

gboolean            (*GstPadAcceptCapsFunction)         (GstPad *pad,
                                                         GstCaps *caps);

Check if pad can accept caps. By default this function will see if caps intersect with the result from gst_pad_get_caps() by can be overridden to perform extra checks.

pad : the GstPad to check
caps : the GstCaps to check
Returns : TRUE if the caps can be accepted by the pad.

gst_pad_set_getcaps_function ()

void                gst_pad_set_getcaps_function        (GstPad *pad,
                                                         GstPadGetCapsFunction getcaps);

Sets the given getcaps function for the pad. getcaps should return the allowable caps for a pad in the context of the element's state, its link to other elements, and the devices or files it has opened. These caps must be a subset of the pad template caps. In the NULL state with no links, getcaps should ideally return the same caps as the pad template. In rare circumstances, an object property can affect the caps returned by getcaps, but this is discouraged.

You do not need to call this function if pad's allowed caps are always the same as the pad template caps. This can only be true if the padtemplate has fixed simple caps.

For most filters, the caps returned by getcaps is directly affected by the allowed caps on other pads. For demuxers and decoders, the caps returned by the srcpad's getcaps function is directly related to the stream data. Again, getcaps should return the most specific caps it reasonably can, since this helps with autoplugging.

Note that the return value from getcaps is owned by the caller, so the caller should unref the caps after usage.

pad : a GstPad.
getcaps : the GstPadGetCapsFunction to set.

GstPadGetCapsFunction ()

GstCaps*            (*GstPadGetCapsFunction)            (GstPad *pad);

Returns a copy of the capabilities of the specified pad. By default this function will return the pad template capabilities, but can optionally be overridden by elements.

pad : the GstPad to get the capabilities of.
Returns : a newly allocated copy GstCaps of the pad.

gst_pad_proxy_getcaps ()

GstCaps*            gst_pad_proxy_getcaps               (GstPad *pad);

Calls gst_pad_get_allowed_caps() for every other pad belonging to the same element as pad, and returns the intersection of the results.

This function is useful as a default getcaps function for an element that can handle any stream format, but requires all its pads to have the same caps. Two such elements are tee and aggregator.

pad : a GstPad to proxy.
Returns : the intersection of the other pads' allowed caps.

gst_pad_set_setcaps_function ()

void                gst_pad_set_setcaps_function        (GstPad *pad,
                                                         GstPadSetCapsFunction setcaps);

Sets the given setcaps function for the pad. The setcaps function will be called whenever a buffer with a new media type is pushed or pulled from the pad. The pad/element needs to update its internal structures to process the new media type. If this new type is not acceptable, the setcaps function should return FALSE.

pad : a GstPad.
setcaps : the GstPadSetCapsFunction to set.

GstPadSetCapsFunction ()

gboolean            (*GstPadSetCapsFunction)            (GstPad *pad,
                                                         GstCaps *caps);

Set caps on pad. By default this function updates the caps of the pad but the function can be overriden by elements to perform extra actions or verifications.

pad : the GstPad to set the capabilities of.
caps : the GstCaps to set
Returns : TRUE if the caps could be set on the pad.

gst_pad_proxy_setcaps ()

gboolean            gst_pad_proxy_setcaps               (GstPad *pad,
                                                         GstCaps *caps);

Calls gst_pad_set_caps() for every other pad belonging to the same element as pad. If gst_pad_set_caps() fails on any pad, the proxy setcaps fails. May be used only during negotiation.

pad : a GstPad to proxy from
caps : the GstCaps to link with
Returns : TRUE if sucessful

gst_pad_fixate_caps ()

void                gst_pad_fixate_caps                 (GstPad *pad,
                                                         GstCaps *caps);

Fixate a caps on the given pad. Modifies the caps in place, so you should make sure that the caps are actually writable (see gst_caps_make_writable()).

pad : a GstPad to fixate
caps : the GstCaps to fixate

gst_pad_set_fixatecaps_function ()

void                gst_pad_set_fixatecaps_function     (GstPad *pad,
                                                         GstPadFixateCapsFunction fixatecaps);

Sets the given fixatecaps function for the pad. The fixatecaps function will be called whenever the default values for a GstCaps needs to be filled in.

pad : a GstPad.
fixatecaps : the GstPadFixateCapsFunction to set.

GstPadFixateCapsFunction ()

void                (*GstPadFixateCapsFunction)         (GstPad *pad,
                                                         GstCaps *caps);

Given possibly unfixed caps caps, let pad use its default prefered format to make a fixed caps. caps should be writable. By default this function will pick the first value of any ranges or lists in the caps but elements can override this function to perform other behaviour.

pad : a GstPad
caps : the GstCaps to fixate

gst_pad_get_fixed_caps_func ()

GstCaps*            gst_pad_get_fixed_caps_func         (GstPad *pad);

A helper function you can use as a GetCaps function that will return the currently negotiated caps or the padtemplate when NULL.

pad : the pad to use
Returns : The currently negotiated caps or the padtemplate.

gst_pad_peer_accept_caps ()

gboolean            gst_pad_peer_accept_caps            (GstPad *pad,
                                                         GstCaps *caps);

Check if the peer of pad accepts caps. If pad has no peer, this function returns TRUE.

pad : a GstPad to check the peer of
caps : a GstCaps to check on the pad
Returns : TRUE if the peer of pad can accept the caps or pad has no peer.

gst_pad_set_activate_function ()

void                gst_pad_set_activate_function       (GstPad *pad,
                                                         GstPadActivateFunction activate);

Sets the given activate function for pad. The activate function will dispatch to gst_pad_activate_push() or gst_pad_activate_pull() to perform the actual activation. Only makes sense to set on sink pads.

Call this function if your sink pad can start a pull-based task.

pad : a GstPad.
activate : the GstPadActivateFunction to set.

GstPadActivateFunction ()

gboolean            (*GstPadActivateFunction)           (GstPad *pad);

This function is called when the pad is activated during the element READY to PAUSED state change. By default this function will call the activate function that puts the pad in push mode but elements can override this function to activate the pad in pull mode if they wish.

pad : a GstPad
Returns : TRUE if the pad could be activated.

gst_pad_set_activatepush_function ()

void                gst_pad_set_activatepush_function   (GstPad *pad,
                                                         GstPadActivateModeFunction activatepush);

Sets the given activate_push function for the pad. An activate_push function prepares the element for pushing. See XXX part-activation.txt for details.

pad : a GstPad.
activatepush : the GstPadActivateModeFunction to set.

gst_pad_set_activatepull_function ()

void                gst_pad_set_activatepull_function   (GstPad *pad,
                                                         GstPadActivateModeFunction activatepull);

Sets the given activate_pull function for the pad. An activate_pull function prepares the element and any upstream connections for pulling. See XXX part-activation.txt for details.

pad : a GstPad.
activatepull : the GstPadActivateModeFunction to set.

GstPadActivateModeFunction ()

gboolean            (*GstPadActivateModeFunction)       (GstPad *pad,
                                                         gboolean active);

The prototype of the push and pull activate functions.

pad : a GstPad
active : activate or deactivate the pad.
Returns : TRUE if the pad could be activated or deactivated.

gst_pad_push ()

GstFlowReturn       gst_pad_push                        (GstPad *pad,
                                                         GstBuffer *buffer);

Pushes a buffer to the peer of pad.

This function will call an installed pad block before triggering any installed pad probes.

If the caps on buffer are different from the currently configured caps on pad, this function will call any installed setcaps function on pad (see gst_pad_set_setcaps_function()). In case of failure to renegotiate the new format, this function returns GST_FLOW_NOT_NEGOTIATED.

The function proceeds calling gst_pad_chain() on the peer pad and returns the value from that function. If pad has no peer, GST_FLOW_NOT_LINKED will be returned.

In all cases, success or failure, the caller loses its reference to buffer after calling this function.

pad : a source GstPad, returns GST_FLOW_ERROR if not.
buffer : the GstBuffer to push returns GST_FLOW_ERROR if not.
Returns : a GstFlowReturn from the peer pad. MT safe.

gst_pad_push_event ()

gboolean            gst_pad_push_event                  (GstPad *pad,
                                                         GstEvent *event);

Sends the event to the peer of the given pad. This function is mainly used by elements to send events to their peer elements.

This function takes owership of the provided event so you should gst_event_ref() it if you want to reuse the event after this call.

pad : a GstPad to push the event to.
event : the GstEvent to send to the pad.
Returns : TRUE if the event was handled. MT safe.

gst_pad_check_pull_range ()

gboolean            gst_pad_check_pull_range            (GstPad *pad);

Checks if a gst_pad_pull_range() can be performed on the peer source pad. This function is used by plugins that want to check if they can use random access on the peer source pad.

The peer sourcepad can implement a custom GstPadCheckGetRangeFunction if it needs to perform some logic to determine if pull_range is possible.

pad : a sink GstPad.
Returns : a gboolean with the result. MT safe.

gst_pad_pull_range ()

GstFlowReturn       gst_pad_pull_range                  (GstPad *pad,
                                                         guint64 offset,
                                                         guint size,
                                                         GstBuffer **buffer);

Pulls a buffer from the peer pad.

This function will first trigger the pad block signal if it was installed.

When pad is not linked GST_FLOW_NOT_LINKED is returned else this function returns the result of gst_pad_get_range() on the peer pad. See gst_pad_get_range() for a list of return values and for the semantics of the arguments of this function.

buffer's caps must either be unset or the same as what is already configured on pad. Renegotiation within a running pull-mode pipeline is not supported.

pad : a sink GstPad, returns GST_FLOW_ERROR if not.
offset : The start offset of the buffer
size : The length of the buffer
buffer : a pointer to hold the GstBuffer, returns GST_FLOW_ERROR if NULL.
Returns : a GstFlowReturn from the peer pad. When this function returns GST_FLOW_OK, buffer will contain a valid GstBuffer that should be freed with gst_buffer_unref() after usage. buffer may not be used or freed when any other return value than GST_FLOW_OK is returned. MT safe.

gst_pad_activate_pull ()

gboolean            gst_pad_activate_pull               (GstPad *pad,
                                                         gboolean active);

Activates or deactivates the given pad in pull mode via dispatching to the pad's activatepullfunc. For use from within pad activation functions only. When called on sink pads, will first proxy the call to the peer pad, which is expected to activate its internally linked pads from within its activate_pull function.

If you don't know what this is, you probably don't want to call it.

pad : the GstPad to activate or deactivate.
active : whether or not the pad should be active.
Returns : TRUE if the operation was successful. MT safe.

gst_pad_activate_push ()

gboolean            gst_pad_activate_push               (GstPad *pad,
                                                         gboolean active);

Activates or deactivates the given pad in push mode via dispatching to the pad's activatepushfunc. For use from within pad activation functions only.

If you don't know what this is, you probably don't want to call it.

pad : the GstPad to activate or deactivate.
active : whether the pad should be active or not.
Returns : TRUE if the operation was successful. MT safe.

gst_pad_send_event ()

gboolean            gst_pad_send_event                  (GstPad *pad,
                                                         GstEvent *event);

Sends the event to the pad. This function can be used by applications to send events in the pipeline.

If pad is a source pad, event should be an upstream event. If pad is a sink pad, event should be a downstream event. For example, you would not send a GST_EVENT_EOS on a src pad; EOS events only propagate downstream. Furthermore, some downstream events have to be serialized with data flow, like EOS, while some can travel out-of-band, like GST_EVENT_FLUSH_START. If the event needs to be serialized with data flow, this function will take the pad's stream lock while calling its event function.

To find out whether an event type is upstream, downstream, or downstream and serialized, see GstEventTypeFlags, gst_event_type_get_flags(), GST_EVENT_IS_UPSTREAM, GST_EVENT_IS_DOWNSTREAM, and GST_EVENT_IS_SERIALIZED. Note that in practice that an application or plugin doesn't need to bother itself with this information; the core handles all necessary locks and checks.

This function takes owership of the provided event so you should gst_event_ref() it if you want to reuse the event after this call.

pad : a GstPad to send the event to.
event : the GstEvent to send to the pad.
Returns : TRUE if the event was handled.

gst_pad_event_default ()

gboolean            gst_pad_event_default               (GstPad *pad,
                                                         GstEvent *event);

Invokes the default event handler for the given pad. End-of-stream and discontinuity events are handled specially, and then the event is sent to all pads internally linked to pad. Note that if there are many possible sink pads that are internally linked to pad, only one will be sent an event. Multi-sinkpad elements should implement custom event handlers.

pad : a GstPad to call the default event handler on.
event : the GstEvent to handle.
Returns : TRUE if the event was sent succesfully.

gst_pad_query ()

gboolean            gst_pad_query                       (GstPad *pad,
                                                         GstQuery *query);

Dispatches a query to a pad. The query should have been allocated by the caller via one of the type-specific allocation functions in gstquery.h. The element is responsible for filling the query with an appropriate response, which should then be parsed with a type-specific query parsing function.

Again, the caller is responsible for both the allocation and deallocation of the query structure.

pad : a GstPad to invoke the default query on.
query : the GstQuery to perform.
Returns : TRUE if the query could be performed.

gst_pad_query_default ()

gboolean            gst_pad_query_default               (GstPad *pad,
                                                         GstQuery *query);

Invokes the default query handler for the given pad. The query is sent to all pads internally linked to pad. Note that if there are many possible sink pads that are internally linked to pad, only one will be sent the query. Multi-sinkpad elements should implement custom query handlers.

pad : a GstPad to call the default query handler on.
query : the GstQuery to handle.
Returns : TRUE if the query was performed succesfully.

gst_pad_query_position ()

gboolean            gst_pad_query_position              (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *cur);

Queries a pad for the stream position.

pad : a GstPad to invoke the position query on.
format : a pointer to the GstFormat asked for. On return contains the GstFormat used.
cur : A location in which to store the current position, or NULL.
Returns : TRUE if the query could be performed.

gst_pad_query_duration ()

gboolean            gst_pad_query_duration              (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *duration);

Queries a pad for the total stream duration.

pad : a GstPad to invoke the duration query on.
format : a pointer to the GstFormat asked for. On return contains the GstFormat used.
duration : A location in which to store the total duration, or NULL.
Returns : TRUE if the query could be performed.

gst_pad_query_convert ()

gboolean            gst_pad_query_convert               (GstPad *pad,
                                                         GstFormat src_format,
                                                         gint64 src_val,
                                                         GstFormat *dest_format,
                                                         gint64 *dest_val);

Queries a pad to convert src_val in src_format to dest_format.

pad : a GstPad to invoke the convert query on.
src_format : a GstFormat to convert from.
src_val : a value to convert.
dest_format : a pointer to the GstFormat to convert to.
dest_val : a pointer to the result.
Returns : TRUE if the query could be performed.

gst_pad_query_peer_position ()

gboolean            gst_pad_query_peer_position         (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *cur);

Queries the peer of a given sink pad for the stream position.

pad : a GstPad on whose peer to invoke the position query on. Must be a sink pad.
format : a pointer to the GstFormat asked for. On return contains the GstFormat used.
cur : A location in which to store the current position, or NULL.
Returns : TRUE if the query could be performed.

gst_pad_query_peer_duration ()

gboolean            gst_pad_query_peer_duration         (GstPad *pad,
                                                         GstFormat *format,
                                                         gint64 *duration);

Queries the peer pad of a given sink pad for the total stream duration.

pad : a GstPad on whose peer pad to invoke the duration query on. Must be a sink pad.
format : a pointer to the GstFormat asked for. On return contains the GstFormat used.
duration : A location in which to store the total duration, or NULL.
Returns : TRUE if the query could be performed.

gst_pad_query_peer_convert ()

gboolean            gst_pad_query_peer_convert          (GstPad *pad,
                                                         GstFormat src_format,
                                                         gint64 src_val,
                                                         GstFormat *dest_format,
                                                         gint64 *dest_val);

Queries the peer pad of a given sink pad to convert src_val in src_format to dest_format.

pad : a GstPad, on whose peer pad to invoke the convert query on. Must be a sink pad.
src_format : a GstFormat to convert from.
src_val : a value to convert.
dest_format : a pointer to the GstFormat to convert to.
dest_val : a pointer to the result.
Returns : TRUE if the query could be performed.

gst_pad_set_query_function ()

void                gst_pad_set_query_function          (GstPad *pad,
                                                         GstPadQueryFunction query);

Set the given query function for the pad.

pad : a GstPad of either direction.
query : the GstPadQueryFunction to set.

GstPadQueryFunction ()

gboolean            (*GstPadQueryFunction)              (GstPad *pad,
                                                         GstQuery *query);

The signature of the query function.

pad : the GstPad to query.
query : the GstQuery object to execute
Returns : TRUE if the query could be performed.

gst_pad_set_query_type_function ()

void                gst_pad_set_query_type_function     (GstPad *pad,
                                                         GstPadQueryTypeFunction type_func);

Set the given query type function for the pad.

pad : a GstPad of either direction.
type_func : the GstPadQueryTypeFunction to set.

GstPadQueryTypeFunction ()

const GstQueryType* (*GstPadQueryTypeFunction)          (GstPad *pad);

The signature of the query types function.

pad : a GstPad to query
Returns : a constant array of query types

gst_pad_get_query_types ()

const GstQueryType* gst_pad_get_query_types             (GstPad *pad);

Get an array of supported queries that can be performed on this pad.

pad : a GstPad.
Returns : a zero-terminated array of GstQueryType.

gst_pad_get_query_types_default ()

const GstQueryType* gst_pad_get_query_types_default     (GstPad *pad);

Invoke the default dispatcher for the query types on the pad.

pad : a GstPad.
Returns : an zero-terminated array of GstQueryType, or NULL if none of the internally-linked pads has a query types function.

gst_pad_set_internal_link_function ()

void                gst_pad_set_internal_link_function  (GstPad *pad,
                                                         GstPadIntLinkFunction intlink);

Sets the given internal link function for the pad.

pad : a GstPad of either direction.
intlink : the GstPadIntLinkFunction to set.

GstPadIntLinkFunction ()

GList*              (*GstPadIntLinkFunction)            (GstPad *pad);

The signature of the internal pad link function.

pad : The GstPad to query.
Returns : a newly allocated GList of pads that are linked to the given pad on the inside of the parent element. The caller must call g_list_free() on it after use.

gst_pad_get_internal_links ()

GList*              gst_pad_get_internal_links          (GstPad *pad);

Gets a list of pads to which the given pad is linked to inside of the parent element. The caller must free this list after use.

pad : the GstPad to get the internal links of.
Returns : a newly allocated GList of pads. Not MT safe.

gst_pad_get_internal_links_default ()

GList*              gst_pad_get_internal_links_default  (GstPad *pad);

Gets a list of pads to which the given pad is linked to inside of the parent element. This is the default handler, and thus returns a list of all of the pads inside the parent element with opposite direction. The caller must free this list after use.

pad : the GstPad to get the internal links of.
Returns : a newly allocated GList of pads, or NULL if the pad has no parent. Not MT safe.

gst_pad_load_and_link ()

void                gst_pad_load_and_link               (xmlNodePtr self,
                                                         GstObject *parent);

Reads the pad definition from the XML node and links the given pad in the element to a pad of an element up in the hierarchy.

self : an xmlNodePtr to read the description from.
parent : the GstObject element that owns the pad.

gst_pad_dispatcher ()

gboolean            gst_pad_dispatcher                  (GstPad *pad,
                                                         GstPadDispatcherFunction dispatch,
                                                         gpointer data);

Invokes the given dispatcher function on each respective peer of all pads that are internally linked to the given pad. The GstPadDispatcherFunction should return TRUE when no further pads need to be processed.

pad : a GstPad to dispatch.
dispatch : the GstDispatcherFunction to call.
data : gpointer user data passed to the dispatcher function.
Returns : TRUE if one of the dispatcher functions returned TRUE.

GstPadDispatcherFunction ()

gboolean            (*GstPadDispatcherFunction)         (GstPad *pad,
                                                         gpointer data);

A dispatcher function is called for all internally linked pads, see gst_pad_dispatcher().

pad : the GstPad that is dispatched.
data : the gpointer to optional user data.
Returns : TRUE if the dispatching procedure has to be stopped.

gst_pad_set_element_private ()

void                gst_pad_set_element_private         (GstPad *pad,
                                                         gpointer priv);

Set the given private data gpointer on the pad. This function can only be used by the element that owns the pad. No locking is performed in this function.

pad : the GstPad to set the private data of.
priv : The private data to attach to the pad.

gst_pad_get_element_private ()

gpointer            gst_pad_get_element_private         (GstPad *pad);

Gets the private data of a pad. No locking is performed in this function.

pad : the GstPad to get the private data of.
Returns : a gpointer to the private data.

gst_pad_chain ()

GstFlowReturn       gst_pad_chain                       (GstPad *pad,
                                                         GstBuffer *buffer);

Chain a buffer to pad.

The function returns GST_FLOW_WRONG_STATE if the pad was flushing.

If the caps on buffer are different from the current caps on pad, this function will call any setcaps function (see gst_pad_set_setcaps_function()) installed on pad. If the new caps are not acceptable for pad, this function returns GST_FLOW_NOT_NEGOTIATED.

The function proceeds calling the chain function installed on pad (see gst_pad_set_chain_function()) and the return value of that function is returned to the caller. GST_FLOW_NOT_SUPPORTED is returned if pad has no chain function.

In all cases, success or failure, the caller loses its reference to buffer after calling this function.

pad : a sink GstPad, returns GST_FLOW_ERROR if not.
buffer : the GstBuffer to send, return GST_FLOW_ERROR if not.
Returns : a GstFlowReturn from the pad. MT safe.

gst_pad_start_task ()

gboolean            gst_pad_start_task                  (GstPad *pad,
                                                         GstTaskFunction func,
                                                         gpointer data);

Starts a task that repeatedly calls func with data. This function is mostly used in pad activation functions to start the dataflow. The GST_PAD_STREAM_LOCK of pad will automatically be acquired before func is called.

pad : the GstPad to start the task of
func : the task function to call
data : data passed to the task function
Returns : a TRUE if the task could be started.

gst_pad_pause_task ()

gboolean            gst_pad_pause_task                  (GstPad *pad);

Pause the task of pad. This function will also make sure that the function executed by the task will effectively stop.

pad : the GstPad to pause the task of
Returns : a TRUE if the task could be paused or FALSE when the pad has no task.

gst_pad_stop_task ()

gboolean            gst_pad_stop_task                   (GstPad *pad);

Stop the task of pad. This function will also make sure that the function executed by the task will effectively stop if not called from the GstTaskFunction.

This function will deadlock if called from the GstTaskFunction of the task. Use gst_task_pause() instead.

Regardless of whether the pad has a task, the stream lock is acquired and released so as to ensure that streaming through this pad has finished.

pad : the GstPad to stop the task of
Returns : a TRUE if the task could be stopped or FALSE on error.

gst_pad_set_active ()

gboolean            gst_pad_set_active                  (GstPad *pad,
                                                         gboolean active);

Activates or deactivates the given pad. Normally called from within core state change functions.

If active, makes sure the pad is active. If it is already active, either in push or pull mode, just return. Otherwise dispatches to the pad's activate function to perform the actual activation.

If not active, checks the pad's current mode and calls gst_pad_activate_push() or gst_pad_activate_pull(), as appropriate, with a FALSE argument.

pad : the GstPad to activate or deactivate.
active : whether or not the pad should be active.
Returns : TRUE if the operation was successful. MT safe.

GST_PAD_GET_STREAM_LOCK()

#define GST_PAD_GET_STREAM_LOCK(pad)    (GST_PAD_CAST(pad)->stream_rec_lock)

Get the stream lock of pad. The stream lock is protecting the resources used in the data processing functions of pad.

pad : a GstPad

GST_PAD_STREAM_LOCK()

#define GST_PAD_STREAM_LOCK(pad)        (g_static_rec_mutex_lock(GST_PAD_GET_STREAM_LOCK(pad)))

Lock the stream lock of pad.

pad : a GstPad

GST_PAD_STREAM_LOCK_FULL()

#define GST_PAD_STREAM_LOCK_FULL(pad,t) (g_static_rec_mutex_lock_full(GST_PAD_GET_STREAM_LOCK(pad), t))

Lock the stream lock of pad t times.

pad : a GstPad
t : the number of times to recursively lock

GST_PAD_STREAM_TRYLOCK()

#define GST_PAD_STREAM_TRYLOCK(pad)     (g_static_rec_mutex_trylock(GST_PAD_GET_STREAM_LOCK(pad)))

Try to Lock the stream lock of the pad, return TRUE if the lock could be taken.

pad : a GstPad

GST_PAD_STREAM_UNLOCK()

#define GST_PAD_STREAM_UNLOCK(pad)      (g_static_rec_mutex_unlock(GST_PAD_GET_STREAM_LOCK(pad)))

Unlock the stream lock of pad.

pad : a GstPad

GST_PAD_STREAM_UNLOCK_FULL()

#define GST_PAD_STREAM_UNLOCK_FULL(pad) (g_static_rec_mutex_unlock_full(GST_PAD_GET_STREAM_LOCK(pad)))

Fully unlock the recursive stream lock of pad, return the number of times pad was locked.

pad : a GstPad

GST_FLOW_IS_FATAL()

#define GST_FLOW_IS_FATAL(ret) ((ret) <= GST_FLOW_UNEXPECTED)

Macro to test if the given GstFlowReturn value indicates a fatal error. This macro is mainly used in elements driving the pipeline to decide whether an error message should be posted on the bus. Note that such elements may also need to post an error message in the GST_FLOW_NOT_LINKED case which is not caught by this macro.

ret : a GstFlowReturn value

GST_FLOW_IS_SUCCESS()

#define GST_FLOW_IS_SUCCESS(ret) ((ret) >= GST_FLOW_OK)

Macro to test if the given GstFlowReturn value indicates a successfull result This macro is mainly used in elements to decide if the processing of a buffer was successfull.

ret : a GstFlowReturn value

Since 0.10.7

Property Details

The "caps" property

  "caps"                     GstCaps               : Read

The capabilities of the pad.


The "direction" property

  "direction"                GstPadDirection       : Read / Write / Construct Only

The direction of the pad.

Default value: GST_PAD_UNKNOWN


The "template" property

  "template"                 GstPadTemplate        : Read / Write

The GstPadTemplate of this pad.

Signal Details

The "have-data" signal

gboolean            user_function                      (GstPad        *pad,
                                                        GstMiniObject *mini_obj,
                                                        gpointer       user_data)      : Run Last / Has Details

Signals that new data is available on the pad. This signal is used internally for implementing pad probes. See gst_pad_add_*_probe functions.

pad : the pad that emitted the signal
mini_obj : new data
user_data : user data set when the signal handler was connected.
Returns : TRUE to keep the data, FALSE to drop it

The "linked" signal

void                user_function                      (GstPad  *pad,
                                                        GstPad  *peer,
                                                        gpointer user_data)      : Run Last

Signals that a pad has been linked to the peer pad.

pad : the pad that emitted the signal
peer : the peer pad that has been connected
user_data : user data set when the signal handler was connected.

The "request-link" signal

void                user_function                      (GstPad  *pad,
                                                        gpointer user_data)      : Run Last

Signals that a pad connection has been requested.

pad : the pad that emitted the signal
peer : the peer pad for which a connection is requested
user_data : user data set when the signal handler was connected.

The "unlinked" signal

void                user_function                      (GstPad  *pad,
                                                        GstPad  *peer,
                                                        gpointer user_data)      : Run Last

Signals that a pad has been unlinked from the peer pad.

pad : the pad that emitted the signal
peer : the peer pad that has been disconnected
user_data : user data set when the signal handler was connected.

See Also

GstPadTemplate, GstElement, GstEvent