## GstPad

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

## Synopsis

    #include <gst/gst.h>

    struct              GstPad;
    enum                GstPadDirection;
    enum                GstPadFlags;
    enum                GstPadLinkReturn;
    #define             GST_PAD_LINK_FAILED                 (ret)
    #define             GST_PAD_LINK_SUCCESSFUL             (ret)
    enum                GstPadLinkCheck;
    enum                GstFlowReturn;
    const gchar *       gst_flow_get_name                   (GstFlowReturn ret);
    GQuark              gst_flow_to_quark                   (GstFlowReturn ret);
    enum                GstPadMode;
    const gchar *       gst_pad_mode_get_name               (GstPadMode mode);

    #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);
    GstPadLinkReturn    gst_pad_link_full                   (GstPad *srcpad,
                                                             GstPad *sinkpad,
                                                             GstPadLinkCheck flags);
    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_allowed_caps            (GstPad *pad);
    GstCaps *           gst_pad_get_current_caps            (GstPad *pad);
    GstCaps *           gst_pad_get_pad_template_caps       (GstPad *pad);
    GstPad *            gst_pad_get_peer                    (GstPad *pad);
    void                gst_pad_use_fixed_caps              (GstPad *pad);
    gboolean            gst_pad_has_current_caps            (GstPad *pad);
    GstEvent *          gst_pad_get_sticky_event            (GstPad *pad,
                                                             GstEventType event_type,
                                                             guint idx);
    gboolean            (*GstPadStickyEventsForeachFunction)
                                                            (GstPad *pad,
                                                             GstEvent **event,
                                                             gpointer user_data);
    void                gst_pad_sticky_events_foreach       (GstPad *pad,
                                                             GstPadStickyEventsForeachFunction foreach_func,
                                                             gpointer user_data);
    gboolean            gst_pad_is_active                   (GstPad *pad);

    enum                GstPadProbeReturn;
    enum                GstPadProbeType;
    struct              GstPadProbeInfo;
    #define             GST_PAD_PROBE_INFO_TYPE             (d)
    #define             GST_PAD_PROBE_INFO_ID               (d)
    #define             GST_PAD_PROBE_INFO_DATA             (d)
    #define             GST_PAD_PROBE_INFO_BUFFER           (d)
    #define             GST_PAD_PROBE_INFO_BUFFER_LIST      (d)
    #define             GST_PAD_PROBE_INFO_EVENT            (d)
    #define             GST_PAD_PROBE_INFO_QUERY            (d)
    GstBuffer *         gst_pad_probe_info_get_buffer       (GstPadProbeInfo *info);
    GstBufferList *     gst_pad_probe_info_get_buffer_list  (GstPadProbeInfo *info);
    GstEvent *          gst_pad_probe_info_get_event        (GstPadProbeInfo *info);
    GstQuery *          gst_pad_probe_info_get_query        (GstPadProbeInfo *info);
    #define             GST_PAD_PROBE_INFO_OFFSET           (d)
    #define             GST_PAD_PROBE_INFO_SIZE             (d)
    GstPadProbeReturn   (*GstPadProbeCallback)              (GstPad *pad,
                                                             GstPadProbeInfo *info,
                                                             gpointer user_data);
    gulong              gst_pad_add_probe                   (GstPad *pad,
                                                             GstPadProbeType mask,
                                                             GstPadProbeCallback callback,
                                                             gpointer user_data,
                                                             GDestroyNotify destroy_data);
    void                gst_pad_remove_probe                (GstPad *pad,
                                                             gulong id);
    gboolean            gst_pad_is_blocked                  (GstPad *pad);
    gboolean            gst_pad_is_blocking                 (GstPad *pad);

    gint64              gst_pad_get_offset                  (GstPad *pad);
    void                gst_pad_set_offset                  (GstPad *pad,
                                                             gint64 offset);

    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);
    #define             gst_pad_set_chain_function          (p,
                                                             f)
    void                gst_pad_set_chain_function_full     (GstPad *pad,
                                                             GstPadChainFunction chain,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    GstFlowReturn       (*GstPadChainFunction)              (GstPad *pad,
                                                             GstObject *parent,
                                                             GstBuffer *buffer);
    #define             gst_pad_set_chain_list_function     (p,
                                                             f)
    void                gst_pad_set_chain_list_function_full
                                                            (GstPad *pad,
                                                             GstPadChainListFunction chainlist,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    GstFlowReturn       (*GstPadChainListFunction)          (GstPad *pad,
                                                             GstObject *parent,
                                                             GstBufferList *list);
    GstFlowReturn       gst_pad_get_range                   (GstPad *pad,
                                                             guint64 offset,
                                                             guint size,
                                                             GstBuffer **buffer);
    #define             gst_pad_set_getrange_function       (p,
                                                             f)
    void                gst_pad_set_getrange_function_full  (GstPad *pad,
                                                             GstPadGetRangeFunction get,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    GstFlowReturn       (*GstPadGetRangeFunction)           (GstPad *pad,
                                                             GstObject *parent,
                                                             guint64 offset,
                                                             guint length,
                                                             GstBuffer **buffer);
    #define             gst_pad_set_event_function          (p,
                                                             f)
    void                gst_pad_set_event_function_full     (GstPad *pad,
                                                             GstPadEventFunction event,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    gboolean            (*GstPadEventFunction)              (GstPad *pad,
                                                             GstObject *parent,
                                                             GstEvent *event);
    #define             gst_pad_set_link_function           (p,
                                                             f)
    void                gst_pad_set_link_function_full      (GstPad *pad,
                                                             GstPadLinkFunction link,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    GstPadLinkReturn    (*GstPadLinkFunction)               (GstPad *pad,
                                                             GstObject *parent,
                                                             GstPad *peer);
    #define             gst_pad_set_unlink_function         (p,
                                                             f)
    void                gst_pad_set_unlink_function_full    (GstPad *pad,
                                                             GstPadUnlinkFunction unlink,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    void                (*GstPadUnlinkFunction)             (GstPad *pad,
                                                             GstObject *parent);
    gboolean            gst_pad_proxy_query_caps            (GstPad *pad,
                                                             GstQuery *query);
    gboolean            gst_pad_proxy_query_accept_caps     (GstPad *pad,
                                                             GstQuery *query);
    #define             gst_pad_set_activate_function       (p,
                                                             f)
    void                gst_pad_set_activate_function_full  (GstPad *pad,
                                                             GstPadActivateFunction activate,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    gboolean            (*GstPadActivateFunction)           (GstPad *pad,
                                                             GstObject *parent);
    #define             gst_pad_set_activatemode_function   (p,
                                                             f)
    void                gst_pad_set_activatemode_function_full
                                                            (GstPad *pad,
                                                             GstPadActivateModeFunction activatemode,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    gboolean            (*GstPadActivateModeFunction)       (GstPad *pad,
                                                             GstObject *parent,
                                                             GstPadMode mode,
                                                             gboolean active);
    gboolean            gst_pad_needs_reconfigure           (GstPad *pad);
    gboolean            gst_pad_check_reconfigure           (GstPad *pad);
    void                gst_pad_mark_reconfigure            (GstPad *pad);
    GstFlowReturn       gst_pad_push                        (GstPad *pad,
                                                             GstBuffer *buffer);
    gboolean            gst_pad_push_event                  (GstPad *pad,
                                                             GstEvent *event);
    GstFlowReturn       gst_pad_push_list                   (GstPad *pad,
                                                             GstBufferList *list);
    GstFlowReturn       gst_pad_pull_range                  (GstPad *pad,
                                                             guint64 offset,
                                                             guint size,
                                                             GstBuffer **buffer);
    gboolean            gst_pad_activate_mode               (GstPad *pad,
                                                             GstPadMode mode,
                                                             gboolean active);
    gboolean            gst_pad_send_event                  (GstPad *pad,
                                                             GstEvent *event);
    gboolean            gst_pad_event_default               (GstPad *pad,
                                                             GstObject *parent,
                                                             GstEvent *event);
    gboolean            gst_pad_query                       (GstPad *pad,
                                                             GstQuery *query);
    gboolean            gst_pad_peer_query                  (GstPad *pad,
                                                             GstQuery *query);
    gboolean            gst_pad_query_default               (GstPad *pad,
                                                             GstObject *parent,
                                                             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_accept_caps           (GstPad *pad,
                                                             GstCaps *caps);
    GstCaps *           gst_pad_query_caps                  (GstPad *pad,
                                                             GstCaps *filter);
    gboolean            gst_pad_peer_query_position         (GstPad *pad,
                                                             GstFormat format,
                                                             gint64 *cur);
    gboolean            gst_pad_peer_query_duration         (GstPad *pad,
                                                             GstFormat format,
                                                             gint64 *duration);
    gboolean            gst_pad_peer_query_convert          (GstPad *pad,
                                                             GstFormat src_format,
                                                             gint64 src_val,
                                                             GstFormat dest_format,
                                                             gint64 *dest_val);
    gboolean            gst_pad_peer_query_accept_caps      (GstPad *pad,
                                                             GstCaps *caps);
    GstCaps *           gst_pad_peer_query_caps             (GstPad *pad,
                                                             GstCaps *filter);
    #define             gst_pad_set_query_function          (p,
                                                             f)
    void                gst_pad_set_query_function_full     (GstPad *pad,
                                                             GstPadQueryFunction query,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    gboolean            (*GstPadQueryFunction)              (GstPad *pad,
                                                             GstObject *parent,
                                                             GstQuery *query);
    #define             gst_pad_set_iterate_internal_links_function(p,
                                                             f)
    void                gst_pad_set_iterate_internal_links_function_full
                                                            (GstPad *pad,
                                                             GstPadIterIntLinkFunction iterintlink,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    GstIterator *       (*GstPadIterIntLinkFunction)        (GstPad *pad,
                                                             GstObject *parent);
    GstIterator *       gst_pad_iterate_internal_links      (GstPad *pad);
    GstIterator *       gst_pad_iterate_internal_links_default
                                                            (GstPad *pad,
                                                             GstObject *parent);
    void                gst_pad_set_element_private         (GstPad *pad,
                                                             gpointer priv);
    gpointer            gst_pad_get_element_private         (GstPad *pad);
    gchar *             gst_pad_create_stream_id            (GstPad *pad,
                                                             GstElement *parent,
                                                             const gchar *stream_id);
    gchar *             gst_pad_create_stream_id_printf     (GstPad *pad,
                                                             GstElement *parent,
                                                             const gchar *stream_id,
                                                             ...);
    gchar *             gst_pad_create_stream_id_printf_valist
                                                            (GstPad *pad,
                                                             GstElement *parent,
                                                             const gchar *stream_id,
                                                             va_list var_args);
    gboolean            (*GstPadForwardFunction)            (GstPad *pad,
                                                             gpointer user_data);
    gboolean            gst_pad_forward                     (GstPad *pad,
                                                             GstPadForwardFunction forward,
                                                             gpointer user_data);

    GstFlowReturn       gst_pad_chain                       (GstPad *pad,
                                                             GstBuffer *buffer);
    GstFlowReturn       gst_pad_chain_list                  (GstPad *pad,
                                                             GstBufferList *list);
    gboolean            gst_pad_start_task                  (GstPad *pad,
                                                             GstTaskFunction func,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);
    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_TRYLOCK              (pad)
    #define             GST_PAD_STREAM_UNLOCK               (pad)

## Object Hierarchy

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

## Properties

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

## Signals

      "linked"                                         : Run Last
      "unlinked"                                       : Run Last

## Description

A GstElement is linked to other elements via "pads", which are extremely light-weight generic link points.

Pads have a GstPadDirection, source pads produce data, sink pads consume data.

Pads are typically created from a GstPadTemplate with `gst_pad_new_from_template()` and are then added to a GstElement. This usually happens when the element is created but it can also happen dynamically based on the data that the element is processing or based on the pads that the application requests.

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.

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

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

After two pads are retrieved from an element with `gst_element_get_pad()`, the pads can be linked 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 can be unlinked again with `gst_pad_unlink()`. `gst_pad_get_peer()` can be used to check what the pad is linked to.

Before dataflow is possible on the pads, they need to be activated with `gst_pad_set_active()`.

`gst_pad_query()` and `gst_pad_peer_query()` can be used to query various properties of the pad and the stream.

To send a GstEvent on a pad, use `gst_pad_send_event()` and `gst_pad_push_event()`. Some events will be sticky on the pad, meaning that after they pass on the pad they can be queried later with `gst_pad_get_sticky_event()` and `gst_pad_sticky_events_foreach()`. `gst_pad_get_current_caps()` and `gst_pad_has_current_caps()` are convenience functions to query the current sticky CAPS event on a pad.

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

The dataflow, events and queries that happen on a pad can be monitored with probes that can be installed with `gst_pad_add_probe()`. `gst_pad_is_blocked()` can be used to check if a block probe is installed on the pad. `gst_pad_is_blocking()` checks if the blocking probe is currently blocking the pad. `gst_pad_remove_probe()` is used to remove a previously installed probe and unblock blocking probes if any.

Pad have an offset that can be retrieved with `gst_pad_get_offset()`. This offset will be applied to the running_time of all data passing over the pad. `gst_pad_set_offset()` can be used to change the offset.

Convenience functions exist to start, pause and stop the task on a pad with `gst_pad_start_task()`, `gst_pad_pause_task()` and `gst_pad_stop_task()` respectively.

Last reviewed on 2012-03-29 (0.11.3)

## Details

### struct GstPad

    struct GstPad {
      gpointer                       element_private;

      GstPadTemplate                *padtemplate;

      GstPadDirection                direction;
    };

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.

### 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_FLAG_BLOCKED          = (GST_OBJECT_FLAG_LAST << 0),
      GST_PAD_FLAG_FLUSHING         = (GST_OBJECT_FLAG_LAST << 1),
      GST_PAD_FLAG_EOS              = (GST_OBJECT_FLAG_LAST << 2),
      GST_PAD_FLAG_BLOCKING         = (GST_OBJECT_FLAG_LAST << 3),
      GST_PAD_FLAG_NEED_PARENT      = (GST_OBJECT_FLAG_LAST << 4),
      GST_PAD_FLAG_NEED_RECONFIGURE = (GST_OBJECT_FLAG_LAST << 5),
      GST_PAD_FLAG_PENDING_EVENTS   = (GST_OBJECT_FLAG_LAST << 6),
      GST_PAD_FLAG_FIXED_CAPS       = (GST_OBJECT_FLAG_LAST << 7),
      GST_PAD_FLAG_PROXY_CAPS       = (GST_OBJECT_FLAG_LAST << 8),
      GST_PAD_FLAG_PROXY_ALLOCATION = (GST_OBJECT_FLAG_LAST << 9),
      GST_PAD_FLAG_PROXY_SCHEDULING = (GST_OBJECT_FLAG_LAST << 10),
      /* padding */
      GST_PAD_FLAG_LAST        = (GST_OBJECT_FLAG_LAST << 16)
    } GstPadFlags;

Pad state flags

`GST_PAD_FLAG_BLOCKED` | is dataflow on a pad blocked
`GST_PAD_FLAG_FLUSHING` | is pad flushing
`GST_PAD_FLAG_EOS` | is pad in EOS state
`GST_PAD_FLAG_BLOCKING` | is pad currently blocking on a buffer or event
`GST_PAD_FLAG_NEED_PARENT` | ensure that there is a parent object before calling into the pad callbacks.
`GST_PAD_FLAG_NEED_RECONFIGURE` | the pad should be reconfigured/renegotiated. The flag has to be unset manually after reconfiguration happened.
`GST_PAD_FLAG_PENDING_EVENTS` | the pad has pending events
`GST_PAD_FLAG_FIXED_CAPS` | the pad is using fixed caps this means that once the caps are set on the pad, the caps query function only returns those caps.
`GST_PAD_FLAG_PROXY_CAPS` | the default event and query handler will forward all events and queries to the internally linked pads instead of discarding them.
`GST_PAD_FLAG_PROXY_ALLOCATION` | the default query handler will forward allocation queries to the internally linked pads instead of discarding them.
`GST_PAD_FLAG_PROXY_SCHEDULING` | the default query handler will forward scheduling queries to the internally linked pads instead of discarding them.
`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 GstPadLinkCheck

    typedef enum {
      GST_PAD_LINK_CHECK_NOTHING       = 0,
      GST_PAD_LINK_CHECK_HIERARCHY     = 1 << 0,
      GST_PAD_LINK_CHECK_TEMPLATE_CAPS = 1 << 1,
      GST_PAD_LINK_CHECK_CAPS          = 1 << 2,

      GST_PAD_LINK_CHECK_DEFAULT       = GST_PAD_LINK_CHECK_HIERARCHY | GST_PAD_LINK_CHECK_CAPS
    } GstPadLinkCheck;

The amount of checking to be done when linking pads. `GST_PAD_LINK_CHECK_CAPS` and `GST_PAD_LINK_CHECK_TEMPLATE_CAPS` are mutually exclusive. If both are specified, expensive but safe `GST_PAD_LINK_CHECK_CAPS` are performed.

### Warning

Only disable some of the checks if you are 100% certain you know the link will not fail because of hierarchy/caps compatibility failures. If uncertain, use the default checks (`GST_PAD_LINK_CHECK_DEFAULT`) or the regular methods for linking the pads.

`GST_PAD_LINK_CHECK_NOTHING` | Don't check hierarchy or caps compatibility.
`GST_PAD_LINK_CHECK_HIERARCHY` | Check the pads have same parents/grandparents. Could be omitted if it is already known that the two elements that own the pads are in the same bin.
`GST_PAD_LINK_CHECK_TEMPLATE_CAPS` | Check if the pads are compatible by using their template caps. This is much faster than `GST_PAD_LINK_CHECK_CAPS`, but would be unsafe e.g. if one pad has `GST_CAPS_ANY`.
`GST_PAD_LINK_CHECK_CAPS` | Check if the pads are compatible by comparing the caps returned by `gst_pad_query_caps()`.
`GST_PAD_LINK_CHECK_DEFAULT` | The default checks done when linking pads (i.e. the ones used by `gst_pad_link()`).

### enum GstFlowReturn

    typedef enum {
      /* custom success starts here */
      GST_FLOW_CUSTOM_SUCCESS_2 = 102,
      GST_FLOW_CUSTOM_SUCCESS_1 = 101,
      GST_FLOW_CUSTOM_SUCCESS = 100,

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

      /* custom error starts here */
      GST_FLOW_CUSTOM_ERROR   = -100,
      GST_FLOW_CUSTOM_ERROR_1 = -101,
      GST_FLOW_CUSTOM_ERROR_2 = -102
    } GstFlowReturn;

The result of passing data to a pad.

Note that the custom return values should not be exposed outside of the element scope.

`GST_FLOW_CUSTOM_SUCCESS_2` | Pre-defined custom success code.
`GST_FLOW_CUSTOM_SUCCESS_1` | Pre-defined custom success code (define your custom success code to this to avoid compiler warnings).
`GST_FLOW_CUSTOM_SUCCESS` | Elements can use values starting from this (and higher) to define custom success codes.
`GST_FLOW_OK` | Data passing was ok.
`GST_FLOW_NOT_LINKED` | Pad is not linked.
`GST_FLOW_FLUSHING` | Pad is flushing.
`GST_FLOW_EOS` | Pad is 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 (and lower) to define custom error codes.
`GST_FLOW_CUSTOM_ERROR_1` | Pre-defined custom error code (define your custom error code to this to avoid compiler warnings).
`GST_FLOW_CUSTOM_ERROR_2` | Pre-defined custom error code.

### gst_flow_get_name ()

    const gchar *       gst_flow_get_name                   (GstFlowReturn ret);

Gets a string representing the given flow return.

`ret` : | a GstFlowReturn to get the name of.
Returns : | a static string with the name of the flow return.

### gst_flow_to_quark ()

    GQuark              gst_flow_to_quark                   (GstFlowReturn ret);

Get the unique quark for the given GstFlowReturn.

`ret` : | a GstFlowReturn to get the quark of.
Returns : | the quark associated with the flow return or 0 if an invalid return was specified.

### enum GstPadMode

    typedef enum {
      GST_PAD_MODE_NONE,
      GST_PAD_MODE_PUSH,
      GST_PAD_MODE_PULL
    } GstPadMode;

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

`GST_PAD_MODE_NONE` | Pad will not handle dataflow
`GST_PAD_MODE_PUSH` | Pad handles dataflow in downstream push mode
`GST_PAD_MODE_PULL` | Pad handles dataflow in upstream pull mode

### gst_pad_mode_get_name ()

    const gchar *       gst_pad_mode_get_name               (GstPadMode mode);

Return the name of a pad mode, for use in debug messages mostly.

`mode` : | the pad mode
Returns : | short mnemonic for pad mode `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. [transfer full]

### 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. Unref after usage. [transfer full]

### 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_link_full ()

    GstPadLinkReturn    gst_pad_link_full                   (GstPad *srcpad,
                                                             GstPad *sinkpad,
                                                             GstPadLinkCheck flags);

Links the source pad and the sink pad.

This variant of gst_pad_link provides a more granular control on the checks being done when linking. While providing some considerable speedups the caller of this method must be aware that wrong usage of those flags can cause severe issues. Refer to the documentation of GstPadLinkCheck for more information.

MT Safe.

`srcpad` : | the source GstPad to link.
`sinkpad` : | the sink GstPad to link.
`flags` : | the checks to validate when linking
Returns : | A result code indicating if the connection worked or what went wrong.

### 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 are compatible so they can be linked.

`srcpad` : | the source GstPad.
`sinkpad` : | the sink GstPad.
Returns : | TRUE if the pads can be linked.

### 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_query_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. [transfer full]

### gst_pad_get_current_caps ()

    GstCaps *           gst_pad_get_current_caps            (GstPad *pad);

Gets the capabilities currently configured on `pad` with the last GST_EVENT_CAPS event.

`pad` : | a GstPad to get the current capabilities of.
Returns : | the current caps of the pad with incremented ref-count.

### gst_pad_get_pad_template_caps ()

    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. Unref after usage. [transfer full]

### 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. [transfer full]

### gst_pad_use_fixed_caps ()

    void                gst_pad_use_fixed_caps              (GstPad *pad);

A helper function you can use that sets the FIXED_CAPS flag This way the default CAPS query will always return the negotiated caps or in case the pad is not negotiated, the padtemplate caps.

The negotiated caps are the caps of the last CAPS event that passed on the pad. Use this function on a pad that, once it negotiated to a CAPS, cannot be renegotiated to something else.

`pad` : | the pad to use

### gst_pad_has_current_caps ()

    gboolean            gst_pad_has_current_caps            (GstPad *pad);

Check if `pad` has caps set on it with a GST_EVENT_CAPS event.

`pad` : | a GstPad to check
Returns : | TRUE when `pad` has caps associated with it.

### gst_pad_get_sticky_event ()

    GstEvent *          gst_pad_get_sticky_event            (GstPad *pad,
                                                             GstEventType event_type,
                                                             guint idx);

Returns a new reference of the sticky event of type `event_type` from the event.

`pad` : | the GstPad to get the event from.
`event_type` : | the GstEventType that should be retrieved.
`idx` : | the index of the event
Returns : | a GstEvent of type `event_type` or NULL when no event of `event_type` was on `pad`. Unref after usage. [transfer full]

### GstPadStickyEventsForeachFunction ()

    gboolean            (*GstPadStickyEventsForeachFunction)
                                                            (GstPad *pad,
                                                             GstEvent **event,
                                                             gpointer user_data);

Callback used by `gst_pad_sticky_events_foreach()`.

When this function returns `TRUE`, the next event will be returned. When `FALSE` is returned, `gst_pad_sticky_events_foreach()` will return.

When `event` is set to NULL, the item will be removed from the list of sticky events. When `event` has been made writable, the new buffer reference can be assigned to `event`. This function is responsible for unreffing the old event when removing or modifying.

`pad` : | the GstPad.
`event` : | a sticky GstEvent.
`user_data` : | the gpointer to optional user data.
Returns : | `TRUE` if the iteration should continue

### gst_pad_sticky_events_foreach ()

    void                gst_pad_sticky_events_foreach       (GstPad *pad,
                                                             GstPadStickyEventsForeachFunction foreach_func,
                                                             gpointer user_data);

Iterates all sticky events on `pad` and calls `foreach_func` for every event. If `foreach_func` returns `FALSE` the iteration is immediately stopped.

`pad` : | the GstPad that should be used for iteration.
`foreach_func` : | the GstPadStickyEventsForeachFunction that should be called for every event. [scope call]
`user_data` : | the optional user data. [closure]

### 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.

### enum GstPadProbeReturn

    typedef enum {
      GST_PAD_PROBE_DROP,
      GST_PAD_PROBE_OK,
      GST_PAD_PROBE_REMOVE,
      GST_PAD_PROBE_PASS,
    } GstPadProbeReturn;

Different return values for the GstPadProbeCallback.

`GST_PAD_PROBE_DROP` | drop data in data probes. For push mode this means that the data item is not sent downstream. For pull mode, it means that the data item is not passed upstream. In both cases, this result code returns GST_FLOW_OK or `TRUE` to the caller.
`GST_PAD_PROBE_OK` | normal probe return value
`GST_PAD_PROBE_REMOVE` | remove probe
`GST_PAD_PROBE_PASS` | pass the data item in the block probe and block on the next item

### enum GstPadProbeType

    typedef enum {
      GST_PAD_PROBE_TYPE_INVALID          = 0,
      /* flags to control blocking */
      GST_PAD_PROBE_TYPE_IDLE             = (1 << 0),
      GST_PAD_PROBE_TYPE_BLOCK            = (1 << 1),
      /* flags to select datatypes */
      GST_PAD_PROBE_TYPE_BUFFER           = (1 << 4),
      GST_PAD_PROBE_TYPE_BUFFER_LIST      = (1 << 5),
      GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM = (1 << 6),
      GST_PAD_PROBE_TYPE_EVENT_UPSTREAM   = (1 << 7),
      GST_PAD_PROBE_TYPE_EVENT_FLUSH      = (1 << 8),
      GST_PAD_PROBE_TYPE_QUERY_DOWNSTREAM = (1 << 9),
      GST_PAD_PROBE_TYPE_QUERY_UPSTREAM   = (1 << 10),
      /* flags to select scheduling mode */
      GST_PAD_PROBE_TYPE_PUSH             = (1 << 12),
      GST_PAD_PROBE_TYPE_PULL             = (1 << 13),

      /* flag combinations */
      GST_PAD_PROBE_TYPE_BLOCKING         = GST_PAD_PROBE_TYPE_IDLE | GST_PAD_PROBE_TYPE_BLOCK,
      GST_PAD_PROBE_TYPE_DATA_DOWNSTREAM  = GST_PAD_PROBE_TYPE_BUFFER | GST_PAD_PROBE_TYPE_BUFFER_LIST | GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM,
      GST_PAD_PROBE_TYPE_DATA_UPSTREAM    = GST_PAD_PROBE_TYPE_EVENT_UPSTREAM,
      GST_PAD_PROBE_TYPE_DATA_BOTH        = GST_PAD_PROBE_TYPE_DATA_DOWNSTREAM | GST_PAD_PROBE_TYPE_DATA_UPSTREAM,
      GST_PAD_PROBE_TYPE_BLOCK_DOWNSTREAM = GST_PAD_PROBE_TYPE_BLOCK | GST_PAD_PROBE_TYPE_DATA_DOWNSTREAM,
      GST_PAD_PROBE_TYPE_BLOCK_UPSTREAM   = GST_PAD_PROBE_TYPE_BLOCK | GST_PAD_PROBE_TYPE_DATA_UPSTREAM,
      GST_PAD_PROBE_TYPE_EVENT_BOTH       = GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM | GST_PAD_PROBE_TYPE_EVENT_UPSTREAM,
      GST_PAD_PROBE_TYPE_QUERY_BOTH       = GST_PAD_PROBE_TYPE_QUERY_DOWNSTREAM | GST_PAD_PROBE_TYPE_QUERY_UPSTREAM,
      GST_PAD_PROBE_TYPE_ALL_BOTH         = GST_PAD_PROBE_TYPE_DATA_BOTH | GST_PAD_PROBE_TYPE_QUERY_BOTH,
      GST_PAD_PROBE_TYPE_SCHEDULING       = GST_PAD_PROBE_TYPE_PUSH | GST_PAD_PROBE_TYPE_PULL
    } GstPadProbeType;

The different probing types that can occur. When either one of `GST_PAD_PROBE_TYPE_IDLE` or `GST_PAD_PROBE_TYPE_BLOCK` is used, the probe will be a blocking probe.

`GST_PAD_PROBE_TYPE_INVALID` | invalid probe type
`GST_PAD_PROBE_TYPE_IDLE` | probe idle pads and block
`GST_PAD_PROBE_TYPE_BLOCK` | probe and block pads
`GST_PAD_PROBE_TYPE_BUFFER` | probe buffers
`GST_PAD_PROBE_TYPE_BUFFER_LIST` | probe buffer lists
`GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM` | probe downstream events
`GST_PAD_PROBE_TYPE_EVENT_UPSTREAM` | probe upstream events
`GST_PAD_PROBE_TYPE_EVENT_FLUSH` | probe flush events. This probe has to be explicitly enabled and is not included in the @`GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM` or @`GST_PAD_PROBE_TYPE_EVENT_UPSTREAM` probe types.
`GST_PAD_PROBE_TYPE_QUERY_DOWNSTREAM` | probe downstream queries
`GST_PAD_PROBE_TYPE_QUERY_UPSTREAM` | probe upstream queries
`GST_PAD_PROBE_TYPE_PUSH` | probe push
`GST_PAD_PROBE_TYPE_PULL` | probe pull
`GST_PAD_PROBE_TYPE_BLOCKING` | probe and block at the next opportunity, at data flow or when idle
`GST_PAD_PROBE_TYPE_DATA_DOWNSTREAM` | probe downstream data (buffers, buffer lists, and events)
`GST_PAD_PROBE_TYPE_DATA_UPSTREAM` | probe upstream data (events)
`GST_PAD_PROBE_TYPE_DATA_BOTH` | probe upstream and downstream data (buffers, buffer lists, and events)
`GST_PAD_PROBE_TYPE_BLOCK_DOWNSTREAM` | probe and block downstream data (buffers, buffer lists, and events)
`GST_PAD_PROBE_TYPE_BLOCK_UPSTREAM` | probe and block upstream data (events)
`GST_PAD_PROBE_TYPE_EVENT_BOTH` | probe upstream and downstream events
`GST_PAD_PROBE_TYPE_QUERY_BOTH` | probe upstream and downstream queries
`GST_PAD_PROBE_TYPE_ALL_BOTH` | probe upstream events and queries and downstream buffers, buffer lists, events and queries
`GST_PAD_PROBE_TYPE_SCHEDULING` | probe push and pull

### struct GstPadProbeInfo

    struct GstPadProbeInfo {
      GstPadProbeType type;
      gulong id;
      gpointer data;
      guint64 offset;
      guint size;
    };

Info passed in the GstPadProbeCallback.

GstPadProbeType `type`; | the current probe type
gulong `id`; | the id of the probe
gpointer `data`; | type specific data, check the `type` field to know the datatype. This field can be NULL.
guint64 `offset`; | offset of pull probe, this field is valid when `type` contains GST_PAD_PROBE_TYPE_PULL
guint `size`; | size of pull probe, this field is valid when `type` contains GST_PAD_PROBE_TYPE_PULL

### GST_PAD_PROBE_INFO_TYPE()

    #define GST_PAD_PROBE_INFO_TYPE(d)         ((d)->type)

### GST_PAD_PROBE_INFO_ID()

    #define GST_PAD_PROBE_INFO_ID(d)           ((d)->id)

### GST_PAD_PROBE_INFO_DATA()

    #define GST_PAD_PROBE_INFO_DATA(d)         ((d)->data)

### GST_PAD_PROBE_INFO_BUFFER()

    #define GST_PAD_PROBE_INFO_BUFFER(d)       GST_BUFFER_CAST(GST_PAD_PROBE_INFO_DATA(d))

### GST_PAD_PROBE_INFO_BUFFER_LIST()

    #define GST_PAD_PROBE_INFO_BUFFER_LIST(d)  GST_BUFFER_LIST_CAST(GST_PAD_PROBE_INFO_DATA(d))

### GST_PAD_PROBE_INFO_EVENT()

    #define GST_PAD_PROBE_INFO_EVENT(d)        GST_EVENT_CAST(GST_PAD_PROBE_INFO_DATA(d))

### GST_PAD_PROBE_INFO_QUERY()

    #define GST_PAD_PROBE_INFO_QUERY(d)        GST_QUERY_CAST(GST_PAD_PROBE_INFO_DATA(d))

### gst_pad_probe_info_get_buffer ()

    GstBuffer *         gst_pad_probe_info_get_buffer       (GstPadProbeInfo *info);

`info` : | a GstPadProbeInfo
Returns : | The GstBuffer from the probe. [transfer none]

### gst_pad_probe_info_get_buffer_list ()

    GstBufferList *     gst_pad_probe_info_get_buffer_list  (GstPadProbeInfo *info);

### gst_pad_probe_info_get_event ()

    GstEvent *          gst_pad_probe_info_get_event        (GstPadProbeInfo *info);

`info` : | a GstPadProbeInfo
Returns : | The GstEvent from the probe. [transfer none]

### gst_pad_probe_info_get_query ()

    GstQuery *          gst_pad_probe_info_get_query        (GstPadProbeInfo *info);

`info` : | a GstPadProbeInfo
Returns : | The GstQuery from the probe. [transfer none]

### GST_PAD_PROBE_INFO_OFFSET()

    #define GST_PAD_PROBE_INFO_OFFSET(d)       ((d)->offset)

### GST_PAD_PROBE_INFO_SIZE()

    #define GST_PAD_PROBE_INFO_SIZE(d)         ((d)->size)

### GstPadProbeCallback ()

    GstPadProbeReturn   (*GstPadProbeCallback)              (GstPad *pad,
                                                             GstPadProbeInfo *info,
                                                             gpointer user_data);

Callback used by `gst_pad_add_probe()`. Gets called to notify about the current blocking type.

The callback is allowed to modify the data pointer in `info`.

`pad` : | the GstPad that is blocked
`info` : | GstPadProbeInfo
`user_data` : | the gpointer to optional user data.
Returns : | a GstPadProbeReturn

### gst_pad_add_probe ()

    gulong              gst_pad_add_probe                   (GstPad *pad,
                                                             GstPadProbeType mask,
                                                             GstPadProbeCallback callback,
                                                             gpointer user_data,
                                                             GDestroyNotify destroy_data);

Be notified of different states of pads. The provided callback is called for every state that matches `mask`.

`pad` : | the GstPad to add the probe to
`mask` : | the probe mask
`callback` : | GstPadProbeCallback that will be called with notifications of the pad state
`user_data` : | user data passed to the callback. [closure]
`destroy_data` : | GDestroyNotify for user_data
Returns : | an id or 0 on error. The id can be used to remove the probe with `gst_pad_remove_probe()`. MT safe.

### gst_pad_remove_probe ()

    void                gst_pad_remove_probe                (GstPad *pad,
                                                             gulong id);

Remove the probe with `id` from `pad`.

MT safe.

`pad` : | the GstPad with the probe
`id` : | the probe id to remove

### 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.

### gst_pad_get_offset ()

    gint64              gst_pad_get_offset                  (GstPad *pad);

Get the offset applied to the running time of `pad`. `pad` has to be a source pad.

`pad` : | a GstPad
Returns : | the offset.

### gst_pad_set_offset ()

    void                gst_pad_set_offset                  (GstPad *pad,
                                                             gint64 offset);

Set the offset that will be applied to the running time of `pad`.

`pad` : | a GstPad
`offset` : | the offset

### 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. [transfer floating]

### 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. [transfer full]

### 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. [transfer full]

### gst_pad_set_chain_function()

    #define gst_pad_set_chain_function(p,f)         gst_pad_set_chain_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_chain_function_full()` with NULL for the user_data and notify.

`p` : | a sink GstPad.
`f` : | the GstPadChainFunction to set.

### gst_pad_set_chain_function_full ()

    void                gst_pad_set_chain_function_full     (GstPad *pad,
                                                             GstPadChainFunction chain,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

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.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `chain` will not be used anymore.

### GstPadChainFunction ()

    GstFlowReturn       (*GstPadChainFunction)              (GstPad *pad,
                                                             GstObject *parent,
                                                             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 bus and return an appropriate GstFlowReturn value.

`pad` : | the sink GstPad that performed the chain.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.
`buffer` : | the GstBuffer that is chained, not `NULL`.
Returns : | GST_FLOW_OK for success

### gst_pad_set_chain_list_function()

    #define gst_pad_set_chain_list_function(p,f)    gst_pad_set_chain_list_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_chain_list_function_full()` with NULL for the user_data and notify.

`p` : | a sink GstPad.
`f` : | the GstPadChainListFunction to set.

### gst_pad_set_chain_list_function_full ()

    void                gst_pad_set_chain_list_function_full
                                                            (GstPad *pad,
                                                             GstPadChainListFunction chainlist,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

Sets the given chain list function for the pad. The chainlist function is called to process a GstBufferList input buffer list. See GstPadChainListFunction for more details.

`pad` : | a sink GstPad.
`chainlist` : | the GstPadChainListFunction to set.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `chainlist` will not be used anymore.

### GstPadChainListFunction ()

    GstFlowReturn       (*GstPadChainListFunction)          (GstPad *pad,
                                                             GstObject *parent,
                                                             GstBufferList *list);

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

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

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

`pad` : | the sink GstPad that performed the chain.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.
`list` : | the GstBufferList that is chained, not `NULL`.
Returns : | GST_FLOW_OK for success

### 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_FLUSHING immediately and `buffer` is `NULL`.

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.

If `buffer` points to a variable holding NULL, a valid new GstBuffer will be placed in `buffer` when this function returns GST_FLOW_OK. The new buffer must be freed with `gst_buffer_unref()` after usage.

When `buffer` points to a variable that points to a valid GstBuffer, the buffer will be filled with the result data when this function returns GST_FLOW_OK. If the provided buffer is larger than `size`, only `size` bytes will be filled in the result buffer and its size will be updated accordingly.

Note that less than `size` bytes can be returned in `buffer` when, for example, an EOS condition is near or when `buffer` is not large enough to hold `size` bytes. The caller should check the result buffer size to get the result size.

When this function returns any other result value than GST_FLOW_OK, `buffer` will be unchanged.

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`. [out callee-allocates]
Returns : | a GstFlowReturn from the pad. MT safe.

### gst_pad_set_getrange_function()

    #define gst_pad_set_getrange_function(p,f)      gst_pad_set_getrange_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_getrange_function_full()` with NULL for the user_data and notify.

`p` : | a source GstPad.
`f` : | the GstPadGetRangeFunction to set.

### gst_pad_set_getrange_function_full ()

    void                gst_pad_set_getrange_function_full  (GstPad *pad,
                                                             GstPadGetRangeFunction get,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

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.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `get` will not be used anymore.

### GstPadGetRangeFunction ()

    GstFlowReturn       (*GstPadGetRangeFunction)           (GstPad *pad,
                                                             GstObject *parent,
                                                             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_mode()` with the GST_PAD_MODE_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_EOS, which corresponds to EOS. In this case `buffer` does not contain a valid buffer.

The buffer size of `buffer` will only be smaller than `length` when `offset` is near the end of the stream. In all other cases, the size of `buffer` must be exactly the requested size.

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.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.
`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 and a valid buffer in `buffer`. Any other return value leaves `buffer` undefined.

### gst_pad_set_event_function()

    #define gst_pad_set_event_function(p,f)         gst_pad_set_event_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_event_function_full()` with NULL for the user_data and notify.

`p` : | a GstPad of either direction.
`f` : | the GstPadEventFunction to set.

### gst_pad_set_event_function_full ()

    void                gst_pad_set_event_function_full     (GstPad *pad,
                                                             GstPadEventFunction event,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

Sets the given event handler for the pad.

`pad` : | a GstPad of either direction.
`event` : | the GstPadEventFunction to set.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `event` will not be used anymore.

### GstPadEventFunction ()

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

Function signature to handle an event for the pad.

`pad` : | the GstPad to handle the event.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.
`event` : | the GstEvent to handle.
Returns : | TRUE if the pad could handle the event.

### gst_pad_set_link_function()

    #define gst_pad_set_link_function(p,f)          gst_pad_set_link_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_link_function_full()` with NULL for the user_data and notify.

`p` : | a GstPad.
`f` : | the GstPadLinkFunction to set.

### gst_pad_set_link_function_full ()

    void                gst_pad_set_link_function_full      (GstPad *pad,
                                                             GstPadLinkFunction link,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

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.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `link` will not be used anymore.

### GstPadLinkFunction ()

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

Function signature to handle a new link on the pad.

`pad` : | the GstPad that is linked.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.
`peer` : | the peer GstPad of the link
Returns : | the result of the link with the specified peer.

### gst_pad_set_unlink_function()

    #define gst_pad_set_unlink_function(p,f)        gst_pad_set_unlink_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_unlink_function_full()` with NULL for the user_data and notify.

`p` : | a GstPad.
`f` : | the GstPadUnlinkFunction to set.

### gst_pad_set_unlink_function_full ()

    void                gst_pad_set_unlink_function_full    (GstPad *pad,
                                                             GstPadUnlinkFunction unlink,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

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.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `unlink` will not be used anymore.

### GstPadUnlinkFunction ()

    void                (*GstPadUnlinkFunction)             (GstPad *pad,
                                                             GstObject *parent);

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

`pad` : | the GstPad that is linked.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.

### gst_pad_proxy_query_caps ()

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

Calls `gst_pad_query_caps()` for all internally linked pads fof `pad` and returns the intersection of the results.

This function is useful as a default caps query 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 adder.

`pad` : | a GstPad to proxy.
`query` : | a CAPS GstQuery.
Returns : | TRUE if `query` could be executed

### gst_pad_proxy_query_accept_caps ()

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

Calls `gst_pad_accept_caps()` for all internally linked pads of `pad` and returns the intersection of the results.

This function is useful as a default accept caps query function for an element that can handle any stream format, but requires caps that are acceptable for all oposite pads.

`pad` : | a GstPad to proxy.
`query` : | an ACCEPT_CAPS GstQuery.
Returns : | TRUE if `query` could be executed

### gst_pad_set_activate_function()

    #define gst_pad_set_activate_function(p,f)      gst_pad_set_activate_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_activate_function_full()` with NULL for the user_data and notify.

`p` : | a GstPad.
`f` : | the GstPadActivateFunction to set.

### gst_pad_set_activate_function_full ()

    void                gst_pad_set_activate_function_full  (GstPad *pad,
                                                             GstPadActivateFunction activate,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

Sets the given activate function for `pad`. The activate function will dispatch to `gst_pad_activate_mode()` 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.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `activate` will not be used anymore.

### GstPadActivateFunction ()

    gboolean            (*GstPadActivateFunction)           (GstPad *pad,
                                                             GstObject *parent);

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
`parent` : | the parent of `pad`
Returns : | TRUE if the pad could be activated.

### gst_pad_set_activatemode_function()

    #define gst_pad_set_activatemode_function(p,f)  gst_pad_set_activatemode_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_activatemode_function_full()` with NULL for the user_data and notify.

`p` : | a GstPad.
`f` : | the GstPadActivateModeFunction to set.

### gst_pad_set_activatemode_function_full ()

    void                gst_pad_set_activatemode_function_full
                                                            (GstPad *pad,
                                                             GstPadActivateModeFunction activatemode,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

Sets the given activate_mode function for the pad. An activate_mode function prepares the element for data passing.

`pad` : | a GstPad.
`activatemode` : | the GstPadActivateModeFunction to set.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `activatemode` will not be used anymore.

### GstPadActivateModeFunction ()

    gboolean            (*GstPadActivateModeFunction)       (GstPad *pad,
                                                             GstObject *parent,
                                                             GstPadMode mode,
                                                             gboolean active);

The prototype of the push and pull activate functions.

`pad` : | a GstPad
`parent` : | the parent of `pad`
`mode` : | the requested activation mode of `pad`
`active` : | activate or deactivate the pad.
Returns : | TRUE if the pad could be activated or deactivated.

### gst_pad_needs_reconfigure ()

    gboolean            gst_pad_needs_reconfigure           (GstPad *pad);

Check the GST_PAD_FLAG_NEED_RECONFIGURE flag on `pad` and return `TRUE` if the flag was set.

`pad` : | the GstPad to check
Returns : | `TRUE` is the GST_PAD_FLAG_NEED_RECONFIGURE flag is set on `pad`.

### gst_pad_check_reconfigure ()

    gboolean            gst_pad_check_reconfigure           (GstPad *pad);

Check and clear the GST_PAD_FLAG_NEED_RECONFIGURE flag on `pad` and return `TRUE` if the flag was set.

`pad` : | the GstPad to check
Returns : | `TRUE` is the GST_PAD_FLAG_NEED_RECONFIGURE flag was set on `pad`.

### gst_pad_mark_reconfigure ()

    void                gst_pad_mark_reconfigure            (GstPad *pad);

Mark a pad for needing reconfiguration. The next call to `gst_pad_check_reconfigure()` will return `TRUE` after this call.

`pad` : | the GstPad to mark

### gst_pad_push ()

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

Pushes a buffer to the peer of `pad`.

This function will call installed block probes before triggering any installed data probes.

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. [transfer full]
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. [transfer full]
Returns : | TRUE if the event was handled. MT safe.

### gst_pad_push_list ()

    GstFlowReturn       gst_pad_push_list                   (GstPad *pad,
                                                             GstBufferList *list);

Pushes a buffer list to the peer of `pad`.

This function will call installed block probes before triggering any installed data probes.

The function proceeds calling the chain function on the peer pad and returns the value from that function. If `pad` has no peer, GST_FLOW_NOT_LINKED will be returned. If the peer pad does not have any installed chainlist function every group buffer of the list will be merged into a normal GstBuffer and chained via `gst_pad_chain()`.

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

`pad` : | a source GstPad, returns GST_FLOW_ERROR if not.
`list` : | the GstBufferList to push returns GST_FLOW_ERROR if not. [transfer full]
Returns : | a GstFlowReturn from the peer pad. 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 or fills up a provided buffer.

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.

If `buffer` points to a variable holding NULL, a valid new GstBuffer will be placed in `buffer` when this function returns GST_FLOW_OK. The new buffer must be freed with `gst_buffer_unref()` after usage. When this function returns any other result value, `buffer` will still point to NULL.

When `buffer` points to a variable that points to a valid GstBuffer, the buffer will be filled with the result data when this function returns GST_FLOW_OK. When this function returns any other result value, `buffer` will be unchanged. If the provided buffer is larger than `size`, only `size` bytes will be filled in the result buffer and its size will be updated accordingly.

Note that less than `size` bytes can be returned in `buffer` when, for example, an EOS condition is near or when `buffer` is not large enough to hold `size` bytes. The caller should check the result buffer size to get the result size.

`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`. [out callee-allocates]
Returns : | a GstFlowReturn from the peer pad. MT safe.

### gst_pad_activate_mode ()

    gboolean            gst_pad_activate_mode               (GstPad *pad,
                                                             GstPadMode mode,
                                                             gboolean active);

Activates or deactivates the given pad in `mode` via dispatching to the pad's activatemodefunc. 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.
`mode` : | the requested activation mode
`active` : | whether or not the pad should be active.
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. [transfer full]
Returns : | TRUE if the event was handled.

### gst_pad_event_default ()

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

Invokes the default event handler for the given pad.

The EOS event will pause the task associated with `pad` before it is forwarded to all internally linked pads,

The the event is sent to all pads internally linked to `pad`. This function takes ownership of `event`.

`pad` : | a GstPad to call the default event handler on.
`parent` : | the parent of `pad` or NULL
`event` : | the GstEvent to handle. [transfer full]
Returns : | TRUE if the event was sent successfully.

### 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. The element that the pad belongs to 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.

Please also note that some queries might need a running pipeline to work.

`pad` : | a GstPad to invoke the default query on.
`query` : | the GstQuery to perform. [transfer none]
Returns : | TRUE if the query could be performed.

### gst_pad_peer_query ()

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

Performs `gst_pad_query()` on the peer of `pad`.

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

`pad` : | a GstPad to invoke the peer query on.
`query` : | the GstQuery to perform. [transfer none]
Returns : | TRUE if the query could be performed. This function returns `FALSE` if `pad` has no peer.

### gst_pad_query_default ()

    gboolean            gst_pad_query_default               (GstPad *pad,
                                                             GstObject *parent,
                                                             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.
`parent` : | the parent of `pad` or NULL
`query` : | the GstQuery to handle. [transfer none]
Returns : | TRUE if the query was performed successfully.

### 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` : | the GstFormat requested
`cur` : | A location in which to store the current position, or NULL. [out]
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` : | the GstFormat requested
`duration` : | a location in which to store the total duration, or NULL. [out][allow-none]
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` : | the GstFormat to convert to.
`dest_val` : | a pointer to the result. [out]
Returns : | TRUE if the query could be performed.

### gst_pad_query_accept_caps ()

    gboolean            gst_pad_query_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_query_caps ()

    GstCaps *           gst_pad_query_caps                  (GstPad *pad,
                                                             GstCaps *filter);

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_get_current_caps()` for that instead. gst_pad_query_caps returns all possible caps a pad can operate with, using the pad's CAPS query function, If the query fails, this function will return `filter`, if not NULL, otherwise ANY.

When called on sinkpads `filter` contains the caps that upstream could produce in the order preferred by upstream. When called on srcpads `filter` contains the caps accepted by downstream in the preffered order. `filter` might be `NULL` but if it is not `NULL` the returned caps will be a subset of `filter`.

Note that this function does not return writable GstCaps, use `gst_caps_make_writable()` before modifying the caps.

`pad` : | a GstPad to get the capabilities of.
`filter` : | suggested GstCaps, or NULL. [allow-none]
Returns : | the caps of the pad with incremented ref-count. [transfer full]

### gst_pad_peer_query_position ()

    gboolean            gst_pad_peer_query_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` : | the GstFormat requested
`cur` : | a location in which to store the current position, or NULL. [out][allow-none]
Returns : | TRUE if the query could be performed.

### gst_pad_peer_query_duration ()

    gboolean            gst_pad_peer_query_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` : | the GstFormat requested
`duration` : | a location in which to store the total duration, or NULL. [out][allow-none]
Returns : | TRUE if the query could be performed.

### gst_pad_peer_query_convert ()

    gboolean            gst_pad_peer_query_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` : | the GstFormat to convert to.
`dest_val` : | a pointer to the result. [out]
Returns : | TRUE if the query could be performed.

### gst_pad_peer_query_accept_caps ()

    gboolean            gst_pad_peer_query_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_peer_query_caps ()

    GstCaps *           gst_pad_peer_query_caps             (GstPad *pad,
                                                             GstCaps *filter);

Gets the capabilities of the peer connected to this pad. Similar to `gst_pad_query_caps()`.

When called on srcpads `filter` contains the caps that upstream could produce in the order preferred by upstream. When called on sinkpads `filter` contains the caps accepted by downstream in the preffered order. `filter` might be `NULL` but if it is not `NULL` the returned caps will be a subset of `filter`.

`pad` : | a GstPad to get the capabilities of.
`filter` : | a GstCaps filter, or NULL. [allow-none]
Returns : | the caps of the peer pad with incremented ref-count. When there is no peer pad, this function returns `filter` or, when `filter` is `NULL`, ANY caps.

### gst_pad_set_query_function()

    #define gst_pad_set_query_function(p,f)   gst_pad_set_query_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_query_function_full()` with NULL for the user_data and notify.

`p` : | a GstPad of either direction.
`f` : | the GstPadQueryFunction to set.

### gst_pad_set_query_function_full ()

    void                gst_pad_set_query_function_full     (GstPad *pad,
                                                             GstPadQueryFunction query,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

Set the given query function for the pad.

`pad` : | a GstPad of either direction.
`query` : | the GstPadQueryFunction to set.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `query` will not be used anymore.

### GstPadQueryFunction ()

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

The signature of the query function.

`pad` : | the GstPad to query.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.
`query` : | the GstQuery object to execute
Returns : | TRUE if the query could be performed.

### gst_pad_set_iterate_internal_links_function()

    #define gst_pad_set_iterate_internal_links_function(p,f) gst_pad_set_iterate_internal_links_function_full((p),(f),NULL,NULL)

Calls `gst_pad_set_iterate_internal_links_function_full()` with NULL for the user_data and notify.

`p` : | a GstPad of either direction.
`f` : | the GstPadIterIntLinkFunction to set.

### gst_pad_set_iterate_internal_links_function_full ()

    void                gst_pad_set_iterate_internal_links_function_full
                                                            (GstPad *pad,
                                                             GstPadIterIntLinkFunction iterintlink,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

Sets the given internal link iterator function for the pad.

`pad` : | a GstPad of either direction.
`iterintlink` : | the GstPadIterIntLinkFunction to set.
`user_data` : | user_data passed to `notify`
`notify` : | notify called when `iterintlink` will not be used anymore.

### GstPadIterIntLinkFunction ()

    GstIterator *       (*GstPadIterIntLinkFunction)        (GstPad *pad,
                                                             GstObject *parent);

The signature of the internal pad link iterator function.

`pad` : | The GstPad to query.
`parent` : | the parent of `pad`. If the GST_PAD_FLAG_NEED_PARENT flag is set, `parent` is guaranteed to be not-NULL and remain valid during the execution of this function.
Returns : | a new GstIterator that will iterate over all pads that are linked to the given pad on the inside of the parent element. the caller must call `gst_iterator_free()` after usage.

### gst_pad_iterate_internal_links ()

    GstIterator *       gst_pad_iterate_internal_links      (GstPad *pad);

Gets an iterator for the pads to which the given pad is linked to inside of the parent element.

Each GstPad element yielded by the iterator will have its refcount increased, so unref after use.

Free-function: gst_iterator_free

`pad` : | the GstPad to get the internal links of.
Returns : | a new GstIterator of GstPad or `NULL` when the pad does not have an iterator function configured. Use `gst_iterator_free()` after usage. [transfer full]

### gst_pad_iterate_internal_links_default ()

    GstIterator *       gst_pad_iterate_internal_links_default
                                                            (GstPad *pad,
                                                             GstObject *parent);

Iterate the list of pads to which the given pad is linked to inside of the parent element. This is the default handler, and thus returns an iterator of all of the pads inside the parent element with opposite direction.

The caller must free this iterator after use with `gst_iterator_free()`.

`pad` : | the GstPad to get the internal links of.
`parent` : | the parent of `pad` or NULL
Returns : | a GstIterator of GstPad, or NULL if `pad` has no parent. Unref each returned pad with `gst_object_unref()`.

### 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. [transfer none]

### gst_pad_create_stream_id ()

    gchar *             gst_pad_create_stream_id            (GstPad *pad,
                                                             GstElement *parent,
                                                             const gchar *stream_id);

Creates a stream-id for the source GstPad `pad` by combining the upstream information with the optional `stream_id` of the stream of `pad`. `pad` must have a parent GstElement and which must have zero or one sinkpad. `stream_id` can only be `NULL` if the parent element of `pad` has only a single source pad.

This function generates an unique stream-id by getting the upstream stream-start event stream ID and appending `stream_id` to it. If the element has no sinkpad it will generate an upstream stream-id by doing an URI query on the element and in the worst case just uses a random number. Source elements that don't implement the URI handler interface should ideally generate a unique, deterministic stream-id manually instead.

`pad` : | A source GstPad
`parent` : | Parent GstElement of `pad`
`stream_id` : | The stream-id. [allow-none]
Returns : | A stream-id for `pad`. `g_free()` after usage.

### gst_pad_create_stream_id_printf ()

    gchar *             gst_pad_create_stream_id_printf     (GstPad *pad,
                                                             GstElement *parent,
                                                             const gchar *stream_id,
                                                             ...);

Creates a stream-id for the source GstPad `pad` by combining the upstream information with the optional `stream_id` of the stream of `pad`. `pad` must have a parent GstElement and which must have zero or one sinkpad. `stream_id` can only be `NULL` if the parent element of `pad` has only a single source pad.

This function generates an unique stream-id by getting the upstream stream-start event stream ID and appending `stream_id` to it. If the element has no sinkpad it will generate an upstream stream-id by doing an URI query on the element and in the worst case just uses a random number. Source elements that don't implement the URI handler interface should ideally generate a unique, deterministic stream-id manually instead.

`pad` : | A source GstPad
`parent` : | Parent GstElement of `pad`
`stream_id` : | The stream-id. [allow-none]
`...` : | parameters for the `stream_id` format string
Returns : | A stream-id for `pad`. `g_free()` after usage.

### gst_pad_create_stream_id_printf_valist ()

    gchar *             gst_pad_create_stream_id_printf_valist
                                                            (GstPad *pad,
                                                             GstElement *parent,
                                                             const gchar *stream_id,
                                                             va_list var_args);

Creates a stream-id for the source GstPad `pad` by combining the upstream information with the optional `stream_id` of the stream of `pad`. `pad` must have a parent GstElement and which must have zero or one sinkpad. `stream_id` can only be `NULL` if the parent element of `pad` has only a single source pad.

This function generates an unique stream-id by getting the upstream stream-start event stream ID and appending `stream_id` to it. If the element has no sinkpad it will generate an upstream stream-id by doing an URI query on the element and in the worst case just uses a random number. Source elements that don't implement the URI handler interface should ideally generate a unique, deterministic stream-id manually instead.

`pad` : | A source GstPad
`parent` : | Parent GstElement of `pad`
`stream_id` : | The stream-id. [allow-none]
`var_args` : | parameters for the `stream_id` format string
Returns : | A stream-id for `pad`. `g_free()` after usage.

### GstPadForwardFunction ()

    gboolean            (*GstPadForwardFunction)            (GstPad *pad,
                                                             gpointer user_data);

A forward function is called for all internally linked pads, see `gst_pad_forward()`.

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

### gst_pad_forward ()

    gboolean            gst_pad_forward                     (GstPad *pad,
                                                             GstPadForwardFunction forward,
                                                             gpointer user_data);

Calls `forward` for all internally linked pads of `pad`. This function deals with dynamically changing internal pads and will make sure that the `forward` function is only called once for each pad.

When `forward` returns TRUE, no further pads will be processed.

`pad` : | a GstPad
`forward` : | a GstPadForwardFunction. [scope call]
`user_data` : | user data passed to `forward`
Returns : | TRUE if one of the dispatcher functions returned TRUE.

### gst_pad_chain ()

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

Chain a buffer to `pad`.

The function returns GST_FLOW_FLUSHING if the pad was flushing.

If the buffer type is not acceptable for `pad` (as negotiated with a preceeding GST_EVENT_CAPS event), 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. [transfer full]
Returns : | a GstFlowReturn from the pad. MT safe.

### gst_pad_chain_list ()

    GstFlowReturn       gst_pad_chain_list                  (GstPad *pad,
                                                             GstBufferList *list);

Chain a bufferlist to `pad`.

The function returns GST_FLOW_FLUSHING if the pad was flushing.

If `pad` was not negotiated properly with a CAPS event, this function returns GST_FLOW_NOT_NEGOTIATED.

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

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

MT safe.

`pad` : | a sink GstPad, returns GST_FLOW_ERROR if not.
`list` : | the GstBufferList to send, return GST_FLOW_ERROR if not. [transfer full]
Returns : | a GstFlowReturn from the pad.

### gst_pad_start_task ()

    gboolean            gst_pad_start_task                  (GstPad *pad,
                                                             GstTaskFunction func,
                                                             gpointer user_data,
                                                             GDestroyNotify notify);

Starts a task that repeatedly calls `func` with `user_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
`user_data` : | user data passed to the task function
`notify` : | called when `user_data` is no longer referenced
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 wait until the function executed by the task is finished if this function is not called from the task function.

`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`, calls `gst_pad_activate_mode()` with the pad's current mode and 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_rec_mutex_lock(GST_PAD_GET_STREAM_LOCK(pad))

Lock the stream lock of `pad`.

`pad` : | a GstPad

### GST_PAD_STREAM_TRYLOCK()

    #define GST_PAD_STREAM_TRYLOCK(pad)     g_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_rec_mutex_unlock(GST_PAD_GET_STREAM_LOCK(pad))

Unlock the stream lock of `pad`.

`pad` : | a GstPad

## 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 `"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 `"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, GstQuery, GstBuffer