GstEvent

GstEvent — Structure describing events that are passed up and down a pipeline

Synopsis

#include <gst/gst.h>

struct              GstEvent;
enum                GstEventTypeFlags;
#define             GST_EVENT_TYPE_BOTH
#define             GST_EVENT_MAKE_TYPE                 (num,
                                                         flags)
enum                GstEventType;
#define             GST_EVENT_TRACE_NAME
#define             GST_EVENT_TYPE                      (event)
#define             GST_EVENT_TYPE_NAME                 (event)
#define             GST_EVENT_TIMESTAMP                 (event)
#define             GST_EVENT_SRC                       (event)
#define             GST_EVENT_IS_UPSTREAM               (ev)
#define             GST_EVENT_IS_DOWNSTREAM             (ev)
#define             GST_EVENT_IS_SERIALIZED             (ev)
GstEventTypeFlags   gst_event_type_get_flags            (GstEventType type);
const gchar *       gst_event_type_get_name             (GstEventType type);
GQuark              gst_event_type_to_quark             (GstEventType type);
GstEvent *          gst_event_ref                       (GstEvent *event);
void                gst_event_unref                     (GstEvent *event);
void                gst_event_replace                   (GstEvent **old_event,
                                                         GstEvent *new_event);
GstEvent *          gst_event_copy                      (const GstEvent *event);
GstEvent *          gst_event_new_custom                (GstEventType type,
                                                         GstStructure *structure);
const GstStructure * gst_event_get_structure            (GstEvent *event);
gboolean            gst_event_has_name                  (GstEvent *event,
                                                         const gchar *name);
guint32             gst_event_get_seqnum                (GstEvent *event);
void                gst_event_set_seqnum                (GstEvent *event,
                                                         guint32 seqnum);
GstEvent *          gst_event_new_flush_start           (void);
GstEvent *          gst_event_new_flush_stop            (void);
GstEvent *          gst_event_new_eos                   (void);
GstEvent *          gst_event_new_new_segment           (gboolean update,
                                                         gdouble rate,
                                                         GstFormat format,
                                                         gint64 start,
                                                         gint64 stop,
                                                         gint64 position);
GstEvent *          gst_event_new_new_segment_full      (gboolean update,
                                                         gdouble rate,
                                                         gdouble applied_rate,
                                                         GstFormat format,
                                                         gint64 start,
                                                         gint64 stop,
                                                         gint64 position);
void                gst_event_parse_new_segment         (GstEvent *event,
                                                         gboolean *update,
                                                         gdouble *rate,
                                                         GstFormat *format,
                                                         gint64 *start,
                                                         gint64 *stop,
                                                         gint64 *position);
void                gst_event_parse_new_segment_full    (GstEvent *event,
                                                         gboolean *update,
                                                         gdouble *rate,
                                                         gdouble *applied_rate,
                                                         GstFormat *format,
                                                         gint64 *start,
                                                         gint64 *stop,
                                                         gint64 *position);
GstEvent *          gst_event_new_tag                   (GstTagList *taglist);
void                gst_event_parse_tag                 (GstEvent *event,
                                                         GstTagList **taglist);
GstEvent *          gst_event_new_buffer_size           (GstFormat format,
                                                         gint64 minsize,
                                                         gint64 maxsize,
                                                         gboolean async);
void                gst_event_parse_buffer_size         (GstEvent *event,
                                                         GstFormat *format,
                                                         gint64 *minsize,
                                                         gint64 *maxsize,
                                                         gboolean *async);
enum                GstQOSType;
GstEvent *          gst_event_new_qos                   (gdouble proportion,
                                                         GstClockTimeDiff diff,
                                                         GstClockTime timestamp);
GstEvent *          gst_event_new_qos_full              (GstQOSType type,
                                                         gdouble proportion,
                                                         GstClockTimeDiff diff,
                                                         GstClockTime timestamp);
void                gst_event_parse_qos                 (GstEvent *event,
                                                         gdouble *proportion,
                                                         GstClockTimeDiff *diff,
                                                         GstClockTime *timestamp);
void                gst_event_parse_qos_full            (GstEvent *event,
                                                         GstQOSType *type,
                                                         gdouble *proportion,
                                                         GstClockTimeDiff *diff,
                                                         GstClockTime *timestamp);
enum                GstSeekType;
enum                GstSeekFlags;
GstEvent *          gst_event_new_seek                  (gdouble rate,
                                                         GstFormat format,
                                                         GstSeekFlags flags,
                                                         GstSeekType start_type,
                                                         gint64 start,
                                                         GstSeekType stop_type,
                                                         gint64 stop);
void                gst_event_parse_seek                (GstEvent *event,
                                                         gdouble *rate,
                                                         GstFormat *format,
                                                         GstSeekFlags *flags,
                                                         GstSeekType *start_type,
                                                         gint64 *start,
                                                         GstSeekType *stop_type,
                                                         gint64 *stop);
GstEvent *          gst_event_new_navigation            (GstStructure *structure);
GstEvent *          gst_event_new_latency               (GstClockTime latency);
void                gst_event_parse_latency             (GstEvent *event,
                                                         GstClockTime *latency);
GstEvent *          gst_event_new_step                  (GstFormat format,
                                                         guint64 amount,
                                                         gdouble rate,
                                                         gboolean flush,
                                                         gboolean intermediate);
void                gst_event_parse_step                (GstEvent *event,
                                                         GstFormat *format,
                                                         guint64 *amount,
                                                         gdouble *rate,
                                                         gboolean *flush,
                                                         gboolean *intermediate);
GstEvent *          gst_event_new_sink_message          (GstMessage *msg);
void                gst_event_parse_sink_message        (GstEvent *event,
                                                         GstMessage **msg);

Description

The event class provides factory methods to construct events for sending and functions to query (parse) received events.

Events are usually created with gst_event_new_*() which takes event-type specific parameters as arguments. To send an event application will usually use gst_element_send_event() and elements will use gst_pad_send_event() or gst_pad_push_event(). The event should be unreffed with gst_event_unref() if it has not been sent.

Events that have been received can be parsed with their respective gst_event_parse_*() functions. It is valid to pass NULL for unwanted details.

Events are passed between elements in parallel to the data stream. Some events are serialized with buffers, others are not. Some events only travel downstream, others only upstream. Some events can travel both upstream and downstream.

The events are used to signal special conditions in the datastream such as EOS (end of stream) or the start of a new stream-segment. Events are also used to flush the pipeline of any pending data.

Most of the event API is used inside plugins. Applications usually only construct and use seek events. To do that gst_event_new_seek() is used to create a seek event. It takes the needed parameters to specify seeking time and mode.

Example 11. performing a seek on a pipeline

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GstEvent *event;
gboolean result;
...
// construct a seek event to play the media from second 2 to 5, flush
// the pipeline to decrease latency.
event = gst_event_new_seek (1.0, 
   GST_FORMAT_TIME, 
   GST_SEEK_FLAG_FLUSH,
   GST_SEEK_TYPE_SET, 2 * GST_SECOND,
   GST_SEEK_TYPE_SET, 5 * GST_SECOND);
...
result = gst_element_send_event (pipeline, event);
if (!result)
  g_warning ("seek failed");
...


Last reviewed on 2006-09-6 (0.10.10)

Details

struct GstEvent

struct GstEvent {
  GstMiniObject mini_object;

  GstEventType  type;
  guint64       timestamp;
  GstObject     *src;

  GstStructure  *structure;
};

A GstEvent.

GstMiniObject mini_object;

the parent structure

GstEventType type;

the GstEventType of the event

guint64 timestamp;

the timestamp of the event

GstObject *src;

the src of the event

GstStructure *structure;

the GstStructure containing the event info.

enum GstEventTypeFlags

typedef enum {
  GST_EVENT_TYPE_UPSTREAM       = 1 << 0,
  GST_EVENT_TYPE_DOWNSTREAM     = 1 << 1,
  GST_EVENT_TYPE_SERIALIZED     = 1 << 2
} GstEventTypeFlags;

GstEventTypeFlags indicate the aspects of the different GstEventType values. You can get the type flags of a GstEventType with the gst_event_type_get_flags() function.

GST_EVENT_TYPE_UPSTREAM

Set if the event can travel upstream.

GST_EVENT_TYPE_DOWNSTREAM

Set if the event can travel downstream.

GST_EVENT_TYPE_SERIALIZED

Set if the event should be serialized with data flow.

GST_EVENT_TYPE_BOTH

#define             GST_EVENT_TYPE_BOTH

The same thing as GST_EVENT_TYPE_UPSTREAM | GST_EVENT_TYPE_DOWNSTREAM.


GST_EVENT_MAKE_TYPE()

#define             GST_EVENT_MAKE_TYPE(num,flags)

when making custom event types, use this macro with the num and the given flags

num :

the event number to create

flags :

the event flags

enum GstEventType

typedef enum {
  GST_EVENT_UNKNOWN               = GST_EVENT_MAKE_TYPE (0, 0),
  /* bidirectional events */
  GST_EVENT_FLUSH_START           = GST_EVENT_MAKE_TYPE (1, FLAG(BOTH)),
  GST_EVENT_FLUSH_STOP            = GST_EVENT_MAKE_TYPE (2, FLAG(BOTH) | FLAG(SERIALIZED)),
  /* downstream serialized events */
  GST_EVENT_EOS                   = GST_EVENT_MAKE_TYPE (5, FLAG(DOWNSTREAM) | FLAG(SERIALIZED)),
  GST_EVENT_NEWSEGMENT            = GST_EVENT_MAKE_TYPE (6, FLAG(DOWNSTREAM) | FLAG(SERIALIZED)),
  GST_EVENT_TAG                   = GST_EVENT_MAKE_TYPE (7, FLAG(DOWNSTREAM) | FLAG(SERIALIZED)),
  GST_EVENT_BUFFERSIZE            = GST_EVENT_MAKE_TYPE (8, FLAG(DOWNSTREAM) | FLAG(SERIALIZED)),
  GST_EVENT_SINK_MESSAGE          = GST_EVENT_MAKE_TYPE (9, FLAG(DOWNSTREAM) | FLAG(SERIALIZED)),
  /* upstream events */
  GST_EVENT_QOS                   = GST_EVENT_MAKE_TYPE (15, FLAG(UPSTREAM)),
  GST_EVENT_SEEK                  = GST_EVENT_MAKE_TYPE (16, FLAG(UPSTREAM)),
  GST_EVENT_NAVIGATION            = GST_EVENT_MAKE_TYPE (17, FLAG(UPSTREAM)),
  GST_EVENT_LATENCY               = GST_EVENT_MAKE_TYPE (18, FLAG(UPSTREAM)),
  GST_EVENT_STEP                  = GST_EVENT_MAKE_TYPE (19, FLAG(UPSTREAM)),

  /* custom events start here */
  GST_EVENT_CUSTOM_UPSTREAM       = GST_EVENT_MAKE_TYPE (32, FLAG(UPSTREAM)),
  GST_EVENT_CUSTOM_DOWNSTREAM     = GST_EVENT_MAKE_TYPE (32, FLAG(DOWNSTREAM) | FLAG(SERIALIZED)),
  GST_EVENT_CUSTOM_DOWNSTREAM_OOB = GST_EVENT_MAKE_TYPE (32, FLAG(DOWNSTREAM)),
  GST_EVENT_CUSTOM_BOTH           = GST_EVENT_MAKE_TYPE (32, FLAG(BOTH) | FLAG(SERIALIZED)),
  GST_EVENT_CUSTOM_BOTH_OOB       = GST_EVENT_MAKE_TYPE (32, FLAG(BOTH))
} GstEventType;

GstEventType lists the standard event types that can be sent in a pipeline.

The custom event types can be used for private messages between elements that can't be expressed using normal GStreamer buffer passing semantics. Custom events carry an arbitrary GstStructure. Specific custom events are distinguished by the name of the structure.

GST_EVENT_UNKNOWN

unknown event.

GST_EVENT_FLUSH_START

Start a flush operation. This event clears all data from the pipeline and unblock all streaming threads.

GST_EVENT_FLUSH_STOP

Stop a flush operation. This event resets the running-time of the pipeline.

GST_EVENT_EOS

End-Of-Stream. No more data is to be expected to follow without a NEWSEGMENT event.

GST_EVENT_NEWSEGMENT

A new media segment follows in the dataflow. The segment events contains information for clipping buffers and converting buffer timestamps to running-time and stream-time.

GST_EVENT_TAG

A new set of metadata tags has been found in the stream.

GST_EVENT_BUFFERSIZE

Notification of buffering requirements. Currently not used yet.

GST_EVENT_SINK_MESSAGE

An event that sinks turn into a message. Used to send messages that should be emitted in sync with rendering. Since: 0.10.26

GST_EVENT_QOS

A quality message. Used to indicate to upstream elements that the downstream elements should adjust their processing rate.

GST_EVENT_SEEK

A request for a new playback position and rate.

GST_EVENT_NAVIGATION

Navigation events are usually used for communicating user requests, such as mouse or keyboard movements, to upstream elements.

GST_EVENT_LATENCY

Notification of new latency adjustment. Sinks will use the latency information to adjust their synchronisation. Since: 0.10.12

GST_EVENT_STEP

A request for stepping through the media. Sinks will usually execute the step operation. Since: 0.10.24

GST_EVENT_CUSTOM_UPSTREAM

Upstream custom event

GST_EVENT_CUSTOM_DOWNSTREAM

Downstream custom event that travels in the data flow.

GST_EVENT_CUSTOM_DOWNSTREAM_OOB

Custom out-of-band downstream event.

GST_EVENT_CUSTOM_BOTH

Custom upstream or downstream event. In-band when travelling downstream.

GST_EVENT_CUSTOM_BOTH_OOB

Custom upstream or downstream out-of-band event.

GST_EVENT_TRACE_NAME

#define GST_EVENT_TRACE_NAME    "GstEvent"

The name used for memory allocation tracing


GST_EVENT_TYPE()

#define GST_EVENT_TYPE(event)           (GST_EVENT_CAST(event)->type)

Get the GstEventType of the event.

event :

the event to query

GST_EVENT_TYPE_NAME()

#define GST_EVENT_TYPE_NAME(event)      (gst_event_type_get_name(GST_EVENT_TYPE(event)))

Get a constant string representation of the GstEventType of the event.

event :

the event to query

GST_EVENT_TIMESTAMP()

#define GST_EVENT_TIMESTAMP(event)      (GST_EVENT_CAST(event)->timestamp)

Get the GstClockTime timestamp of the event. This is the time when the event was created.

event :

the event to query

GST_EVENT_SRC()

#define GST_EVENT_SRC(event)            (GST_EVENT_CAST(event)->src)

The source GstObject that generated this event.

event :

the event to query

GST_EVENT_IS_UPSTREAM()

#define GST_EVENT_IS_UPSTREAM(ev)       !!(GST_EVENT_TYPE (ev) & GST_EVENT_TYPE_UPSTREAM)

Check if an event can travel upstream.

ev :

the event to query

GST_EVENT_IS_DOWNSTREAM()

#define GST_EVENT_IS_DOWNSTREAM(ev)     !!(GST_EVENT_TYPE (ev) & GST_EVENT_TYPE_DOWNSTREAM)

Check if an event can travel downstream.

ev :

the event to query

GST_EVENT_IS_SERIALIZED()

#define GST_EVENT_IS_SERIALIZED(ev)     !!(GST_EVENT_TYPE (ev) & GST_EVENT_TYPE_SERIALIZED)

Check if an event is serialized with the data stream.

ev :

the event to query

gst_event_type_get_flags ()

GstEventTypeFlags   gst_event_type_get_flags            (GstEventType type);

Gets the GstEventTypeFlags associated with type.

type :

a GstEventType

Returns :

a GstEventTypeFlags.

gst_event_type_get_name ()

const gchar *       gst_event_type_get_name             (GstEventType type);

Get a printable name for the given event type. Do not modify or free.

type :

the event type

Returns :

a reference to the static name of the event.

gst_event_type_to_quark ()

GQuark              gst_event_type_to_quark             (GstEventType type);

Get the unique quark for the given event type.

type :

the event type

Returns :

the quark associated with the event type

gst_event_ref ()

GstEvent *          gst_event_ref                       (GstEvent *event);

Increase the refcount of this event.

event :

The event to refcount

Returns :

event (for convenience when doing assignments). [transfer full]

gst_event_unref ()

void                gst_event_unref                     (GstEvent *event);

Decrease the refcount of an event, freeing it if the refcount reaches 0.

event :

the event to refcount. [transfer full]

gst_event_replace ()

void                gst_event_replace                   (GstEvent **old_event,
                                                         GstEvent *new_event);

Modifies a pointer to a GstEvent to point to a different GstEvent. The modification is done atomically (so this is useful for ensuring thread safety in some cases), and the reference counts are updated appropriately (the old event is unreffed, the new one is reffed).

Either new_event or the GstEvent pointed to by old_event may be NULL.

old_event :

pointer to a pointer to a GstEvent to be replaced. [inout][transfer full]

new_event :

pointer to a GstEvent that will replace the event pointed to by old_event. [allow-none][transfer none]

Since 0.10.3


gst_event_copy ()

GstEvent *          gst_event_copy                      (const GstEvent *event);

Copy the event using the event specific copy function.

event :

The event to copy

Returns :

the new event. [transfer full]

gst_event_new_custom ()

GstEvent *          gst_event_new_custom                (GstEventType type,
                                                         GstStructure *structure);

Create a new custom-typed event. This can be used for anything not handled by other event-specific functions to pass an event to another element.

Make sure to allocate an event type with the GST_EVENT_MAKE_TYPE macro, assigning a free number and filling in the correct direction and serialization flags.

New custom events can also be created by subclassing the event type if needed.

type :

The type of the new event

structure :

the structure for the event. The event will take ownership of the structure. [transfer full]

Returns :

the new custom event. [transfer full]

gst_event_get_structure ()

const GstStructure * gst_event_get_structure            (GstEvent *event);

Access the structure of the event.

event :

The GstEvent.

Returns :

The structure of the event. The structure is still owned by the event, which means that you should not free it and that the pointer becomes invalid when you free the event. MT safe.

gst_event_has_name ()

gboolean            gst_event_has_name                  (GstEvent *event,
                                                         const gchar *name);

Checks if event has the given name. This function is usually used to check the name of a custom event.

event :

The GstEvent.

name :

name to check

Returns :

TRUE if name matches the name of the event structure.

Since 0.10.20


gst_event_get_seqnum ()

guint32             gst_event_get_seqnum                (GstEvent *event);

Retrieve the sequence number of a event.

Events have ever-incrementing sequence numbers, which may also be set explicitly via gst_event_set_seqnum(). Sequence numbers are typically used to indicate that a event corresponds to some other set of events or messages, for example an EOS event corresponding to a SEEK event. It is considered good practice to make this correspondence when possible, though it is not required.

Note that events and messages share the same sequence number incrementor; two events or messages will never have the same sequence number unless that correspondence was made explicitly.

event :

A GstEvent.

Returns :

The event's sequence number. MT safe.

Since 0.10.22


gst_event_set_seqnum ()

void                gst_event_set_seqnum                (GstEvent *event,
                                                         guint32 seqnum);

Set the sequence number of a event.

This function might be called by the creator of a event to indicate that the event relates to other events or messages. See gst_event_get_seqnum() for more information.

MT safe.

event :

A GstEvent.

seqnum :

A sequence number.

Since 0.10.22


gst_event_new_flush_start ()

GstEvent *          gst_event_new_flush_start           (void);

Allocate a new flush start event. The flush start event can be sent upstream and downstream and travels out-of-bounds with the dataflow.

It marks pads as being flushing and will make them return GST_FLOW_WRONG_STATE when used for data flow with gst_pad_push(), gst_pad_chain(), gst_pad_alloc_buffer(), gst_pad_get_range() and gst_pad_pull_range(). Any event (except a GST_EVENT_FLUSH_STOP) received on a flushing pad will return FALSE immediately.

Elements should unlock any blocking functions and exit their streaming functions as fast as possible when this event is received.

This event is typically generated after a seek to flush out all queued data in the pipeline so that the new media is played as soon as possible.

Returns :

a new flush start event. [transfer full]

gst_event_new_flush_stop ()

GstEvent *          gst_event_new_flush_stop            (void);

Allocate a new flush stop event. The flush stop event can be sent upstream and downstream and travels serialized with the dataflow. It is typically sent after sending a FLUSH_START event to make the pads accept data again.

Elements can process this event synchronized with the dataflow since the preceeding FLUSH_START event stopped the dataflow.

This event is typically generated to complete a seek and to resume dataflow.

Returns :

a new flush stop event. [transfer full]

gst_event_new_eos ()

GstEvent *          gst_event_new_eos                   (void);

Create a new EOS event. The eos event can only travel downstream synchronized with the buffer flow. Elements that receive the EOS event on a pad can return GST_FLOW_UNEXPECTED as a GstFlowReturn when data after the EOS event arrives.

The EOS event will travel down to the sink elements in the pipeline which will then post the GST_MESSAGE_EOS on the bus after they have finished playing any buffered data.

When all sinks have posted an EOS message, an EOS message is forwarded to the application.

The EOS event itself will not cause any state transitions of the pipeline.

Returns :

the new EOS event. [transfer full]

gst_event_new_new_segment ()

GstEvent *          gst_event_new_new_segment           (gboolean update,
                                                         gdouble rate,
                                                         GstFormat format,
                                                         gint64 start,
                                                         gint64 stop,
                                                         gint64 position);

Allocate a new newsegment event with the given format/values tripplets

This method calls gst_event_new_new_segment_full() passing a default value of 1.0 for applied_rate

update :

is this segment an update to a previous one

rate :

a new rate for playback

format :

The format of the segment values

start :

the start value of the segment

stop :

the stop value of the segment

position :

stream position

Returns :

a new newsegment event. [transfer full]

gst_event_new_new_segment_full ()

GstEvent *          gst_event_new_new_segment_full      (gboolean update,
                                                         gdouble rate,
                                                         gdouble applied_rate,
                                                         GstFormat format,
                                                         gint64 start,
                                                         gint64 stop,
                                                         gint64 position);

Allocate a new newsegment event with the given format/values triplets.

The newsegment event marks the range of buffers to be processed. All data not within the segment range is not to be processed. This can be used intelligently by plugins to apply more efficient methods of skipping unneeded data. The valid range is expressed with the start and stop values.

The position value of the segment is used in conjunction with the start value to convert the buffer timestamps into the stream time. This is usually done in sinks to report the current stream_time. position represents the stream_time of a buffer carrying a timestamp of start. position cannot be -1.

start cannot be -1, stop can be -1. If there is a valid stop given, it must be greater or equal the start, including when the indicated playback rate is < 0.

The applied_rate value provides information about any rate adjustment that has already been made to the timestamps and content on the buffers of the stream. (rate * applied_rate) should always equal the rate that has been requested for playback. For example, if an element has an input segment with intended playback rate of 2.0 and applied_rate of 1.0, it can adjust incoming timestamps and buffer content by half and output a newsegment event with rate of 1.0 and applied_rate of 2.0

After a newsegment event, the buffer stream time is calculated with:

position + (TIMESTAMP(buf) - start) * ABS (rate * applied_rate)

update :

Whether this segment is an update to a previous one

rate :

A new rate for playback

applied_rate :

The rate factor which has already been applied

format :

The format of the segment values

start :

The start value of the segment

stop :

The stop value of the segment

position :

stream position

Returns :

a new newsegment event. [transfer full]

Since 0.10.6


gst_event_parse_new_segment ()

void                gst_event_parse_new_segment         (GstEvent *event,
                                                         gboolean *update,
                                                         gdouble *rate,
                                                         GstFormat *format,
                                                         gint64 *start,
                                                         gint64 *stop,
                                                         gint64 *position);

Get the update flag, rate, format, start, stop and position in the newsegment event. In general, gst_event_parse_new_segment_full() should be used instead of this, to also retrieve the applied_rate value of the segment. See gst_event_new_new_segment_full() for a full description of the newsegment event.

event :

The event to query

update :

A pointer to the update flag of the segment. [out]

rate :

A pointer to the rate of the segment. [out]

format :

A pointer to the format of the newsegment values. [out]

start :

A pointer to store the start value in. [out]

stop :

A pointer to store the stop value in. [out]

position :

A pointer to store the stream time in. [out]

gst_event_parse_new_segment_full ()

void                gst_event_parse_new_segment_full    (GstEvent *event,
                                                         gboolean *update,
                                                         gdouble *rate,
                                                         gdouble *applied_rate,
                                                         GstFormat *format,
                                                         gint64 *start,
                                                         gint64 *stop,
                                                         gint64 *position);

Get the update, rate, applied_rate, format, start, stop and position in the newsegment event. See gst_event_new_new_segment_full() for a full description of the newsegment event.

event :

The event to query

update :

A pointer to the update flag of the segment. [out]

rate :

A pointer to the rate of the segment. [out]

applied_rate :

A pointer to the applied_rate of the segment. [out]

format :

A pointer to the format of the newsegment values. [out]

start :

A pointer to store the start value in. [out]

stop :

A pointer to store the stop value in. [out]

position :

A pointer to store the stream time in. [out]

Since 0.10.6


gst_event_new_tag ()

GstEvent *          gst_event_new_tag                   (GstTagList *taglist);

Generates a metadata tag event from the given taglist.

taglist :

metadata list. The event will take ownership of the taglist. [transfer full]

Returns :

a new GstEvent. [transfer full]

gst_event_parse_tag ()

void                gst_event_parse_tag                 (GstEvent *event,
                                                         GstTagList **taglist);

Parses a tag event and stores the results in the given taglist location. No reference to the taglist will be returned, it remains valid only until the event is freed. Don't modify or free the taglist, make a copy if you want to modify it or store it for later use.

event :

a tag event

taglist :

pointer to metadata list. [out][transfer none]

gst_event_new_buffer_size ()

GstEvent *          gst_event_new_buffer_size           (GstFormat format,
                                                         gint64 minsize,
                                                         gint64 maxsize,
                                                         gboolean async);

Create a new buffersize event. The event is sent downstream and notifies elements that they should provide a buffer of the specified dimensions.

When the async flag is set, a thread boundary is preferred.

format :

buffer format

minsize :

minimum buffer size

maxsize :

maximum buffer size

async :

thread behavior

Returns :

a new GstEvent. [transfer full]

gst_event_parse_buffer_size ()

void                gst_event_parse_buffer_size         (GstEvent *event,
                                                         GstFormat *format,
                                                         gint64 *minsize,
                                                         gint64 *maxsize,
                                                         gboolean *async);

Get the format, minsize, maxsize and async-flag in the buffersize event.

event :

The event to query

format :

A pointer to store the format in. [out]

minsize :

A pointer to store the minsize in. [out]

maxsize :

A pointer to store the maxsize in. [out]

async :

A pointer to store the async-flag in. [out]

enum GstQOSType

typedef enum {
  GST_QOS_TYPE_OVERFLOW        = 0,
  GST_QOS_TYPE_UNDERFLOW       = 1,
  GST_QOS_TYPE_THROTTLE        = 2
} GstQOSType;

The different types of QoS events that can be given to the gst_event_new_qos_full() method.

GST_QOS_TYPE_OVERFLOW

The QoS event type that is produced when downstream elements are producing data too quickly and the element can't keep up processing the data. Upstream should reduce their processing rate. This type is also used when buffers arrive early or in time.

GST_QOS_TYPE_UNDERFLOW

The QoS event type that is produced when downstream elements are producing data too slowly and need to speed up their processing rate.

GST_QOS_TYPE_THROTTLE

The QoS event type that is produced when the application enabled throttling to limit the datarate.

Since 0.10.33


gst_event_new_qos ()

GstEvent *          gst_event_new_qos                   (gdouble proportion,
                                                         GstClockTimeDiff diff,
                                                         GstClockTime timestamp);

Allocate a new qos event with the given values. This function calls gst_event_new_qos_full() with the type set to GST_QOS_TYPE_OVERFLOW when diff is negative (buffers are in time) and GST_QOS_TYPE_UNDERFLOW when diff is positive (buffers are late).

proportion :

the proportion of the qos message

diff :

The time difference of the last Clock sync

timestamp :

The timestamp of the buffer

Returns :

a new QOS event. [transfer full]

gst_event_new_qos_full ()

GstEvent *          gst_event_new_qos_full              (GstQOSType type,
                                                         gdouble proportion,
                                                         GstClockTimeDiff diff,
                                                         GstClockTime timestamp);

Allocate a new qos event with the given values. The QOS event is generated in an element that wants an upstream element to either reduce or increase its rate because of high/low CPU load or other resource usage such as network performance or throttling. Typically sinks generate these events for each buffer they receive.

type indicates the reason for the QoS event. GST_QOS_TYPE_OVERFLOW is used when a buffer arrived in time or when the sink cannot keep up with the upstream datarate. GST_QOS_TYPE_UNDERFLOW is when the sink is not receiving buffers fast enough and thus has to drop late buffers. GST_QOS_TYPE_THROTTLE is used when the datarate is artificially limited by the application, for example to reduce power consumption.

proportion indicates the real-time performance of the streaming in the element that generated the QoS event (usually the sink). The value is generally computed based on more long term statistics about the streams timestamps compared to the clock. A value < 1.0 indicates that the upstream element is producing data faster than real-time. A value > 1.0 indicates that the upstream element is not producing data fast enough. 1.0 is the ideal proportion value. The proportion value can safely be used to lower or increase the quality of the element.

diff is the difference against the clock in running time of the last buffer that caused the element to generate the QOS event. A negative value means that the buffer with timestamp arrived in time. A positive value indicates how late the buffer with timestamp was. When throttling is enabled, diff will be set to the requested throttling interval.

timestamp is the timestamp of the last buffer that cause the element to generate the QOS event. It is expressed in running time and thus an ever increasing value.

The upstream element can use the diff and timestamp values to decide whether to process more buffers. For possitive diff, all buffers with timestamp <= timestamp + diff will certainly arrive late in the sink as well. A (negative) diff value so that timestamp + diff would yield a result smaller than 0 is not allowed.

The application can use general event probes to intercept the QoS event and implement custom application specific QoS handling.

type :

the QoS type

proportion :

the proportion of the qos message

diff :

The time difference of the last Clock sync

timestamp :

The timestamp of the buffer

Returns :

a new QOS event. [transfer full]

Since 0.10.33


gst_event_parse_qos ()

void                gst_event_parse_qos                 (GstEvent *event,
                                                         gdouble *proportion,
                                                         GstClockTimeDiff *diff,
                                                         GstClockTime *timestamp);

Get the proportion, diff and timestamp in the qos event. See gst_event_new_qos() for more information about the different QoS values.

event :

The event to query

proportion :

A pointer to store the proportion in. [out]

diff :

A pointer to store the diff in. [out]

timestamp :

A pointer to store the timestamp in. [out]

gst_event_parse_qos_full ()

void                gst_event_parse_qos_full            (GstEvent *event,
                                                         GstQOSType *type,
                                                         gdouble *proportion,
                                                         GstClockTimeDiff *diff,
                                                         GstClockTime *timestamp);

Get the type, proportion, diff and timestamp in the qos event. See gst_event_new_qos_full() for more information about the different QoS values.

event :

The event to query

type :

A pointer to store the QoS type in. [out]

proportion :

A pointer to store the proportion in. [out]

diff :

A pointer to store the diff in. [out]

timestamp :

A pointer to store the timestamp in. [out]

Since 0.10.33


enum GstSeekType

typedef enum {
  /* one of these */
  GST_SEEK_TYPE_NONE            = 0,
  GST_SEEK_TYPE_CUR             = 1,
  GST_SEEK_TYPE_SET             = 2,
  GST_SEEK_TYPE_END             = 3
} GstSeekType;

The different types of seek events. When constructing a seek event with gst_event_new_seek(), a format, a seek method and optional flags are to be provided. The seek event is then inserted into the graph with gst_pad_send_event() or gst_element_send_event().

GST_SEEK_TYPE_NONE

no change in position is required

GST_SEEK_TYPE_CUR

change relative to currently configured segment. This can't be used to seek relative to the current playback position - do a position query, calculate the desired position and then do an absolute position seek instead if that's what you want to do.

GST_SEEK_TYPE_SET

absolute position is requested

GST_SEEK_TYPE_END

relative position to duration is requested

enum GstSeekFlags

typedef enum {
  GST_SEEK_FLAG_NONE            = 0,
  GST_SEEK_FLAG_FLUSH           = (1 << 0),
  GST_SEEK_FLAG_ACCURATE        = (1 << 1),
  GST_SEEK_FLAG_KEY_UNIT        = (1 << 2),
  GST_SEEK_FLAG_SEGMENT         = (1 << 3),
  GST_SEEK_FLAG_SKIP            = (1 << 4)
} GstSeekFlags;

Flags to be used with gst_element_seek() or gst_event_new_seek(). All flags can be used together.

A non flushing seek might take some time to perform as the currently playing data in the pipeline will not be cleared.

An accurate seek might be slower for formats that don't have any indexes or timestamp markers in the stream. Specifying this flag might require a complete scan of the file in those cases.

When performing a segment seek: after the playback of the segment completes, no EOS will be emmited by the element that performed the seek, but a GST_MESSAGE_SEGMENT_DONE message will be posted on the bus by the element. When this message is posted, it is possible to send a new seek event to continue playback. With this seek method it is possible to perform seamless looping or simple linear editing.

When doing fast forward (rate > 1.0) or fast reverse (rate < -1.0) trickmode playback, the GST_SEEK_FLAG_SKIP flag can be used to instruct decoders and demuxers to adjust the playback rate by skipping frames. This can improve performance and decrease CPU usage because not all frames need to be decoded.

Also see part-seeking.txt in the GStreamer design documentation for more details on the meaning of these flags and the behaviour expected of elements that handle them.

GST_SEEK_FLAG_NONE

no flag

GST_SEEK_FLAG_FLUSH

flush pipeline

GST_SEEK_FLAG_ACCURATE

accurate position is requested, this might be considerably slower for some formats.

GST_SEEK_FLAG_KEY_UNIT

seek to the nearest keyframe. This might be faster but less accurate.

GST_SEEK_FLAG_SEGMENT

perform a segment seek.

GST_SEEK_FLAG_SKIP

when doing fast foward or fast reverse playback, allow elements to skip frames instead of generating all frames. Since 0.10.22.

gst_event_new_seek ()

GstEvent *          gst_event_new_seek                  (gdouble rate,
                                                         GstFormat format,
                                                         GstSeekFlags flags,
                                                         GstSeekType start_type,
                                                         gint64 start,
                                                         GstSeekType stop_type,
                                                         gint64 stop);

Allocate a new seek event with the given parameters.

The seek event configures playback of the pipeline between start to stop at the speed given in rate, also called a playback segment. The start and stop values are expressed in format.

A rate of 1.0 means normal playback rate, 2.0 means double speed. Negatives values means backwards playback. A value of 0.0 for the rate is not allowed and should be accomplished instead by PAUSING the pipeline.

A pipeline has a default playback segment configured with a start position of 0, a stop position of -1 and a rate of 1.0. The currently configured playback segment can be queried with GST_QUERY_SEGMENT.

start_type and stop_type specify how to adjust the currently configured start and stop fields in playback segment. Adjustments can be made relative or absolute to the last configured values. A type of GST_SEEK_TYPE_NONE means that the position should not be updated.

When the rate is positive and start has been updated, playback will start from the newly configured start position.

For negative rates, playback will start from the newly configured stop position (if any). If the stop position if updated, it must be different from -1 for negative rates.

It is not possible to seek relative to the current playback position, to do this, PAUSE the pipeline, query the current playback position with GST_QUERY_POSITION and update the playback segment current position with a GST_SEEK_TYPE_SET to the desired position.

rate :

The new playback rate

format :

The format of the seek values

flags :

The optional seek flags

start_type :

The type and flags for the new start position

start :

The value of the new start position

stop_type :

The type and flags for the new stop position

stop :

The value of the new stop position

Returns :

a new seek event. [transfer full]

gst_event_parse_seek ()

void                gst_event_parse_seek                (GstEvent *event,
                                                         gdouble *rate,
                                                         GstFormat *format,
                                                         GstSeekFlags *flags,
                                                         GstSeekType *start_type,
                                                         gint64 *start,
                                                         GstSeekType *stop_type,
                                                         gint64 *stop);

Parses a seek event and stores the results in the given result locations.

event :

a seek event

rate :

result location for the rate. [out]

format :

result location for the stream format. [out]

flags :

result location for the GstSeekFlags. [out]

start_type :

result location for the GstSeekType of the start position. [out]

start :

result location for the start postion expressed in format. [out]

stop_type :

result location for the GstSeekType of the stop position. [out]

stop :

result location for the stop postion expressed in format. [out]

gst_event_new_navigation ()

GstEvent *          gst_event_new_navigation            (GstStructure *structure);

Create a new navigation event from the given description.

structure :

description of the event. The event will take ownership of the structure. [transfer full]

Returns :

a new GstEvent. [transfer full]

gst_event_new_latency ()

GstEvent *          gst_event_new_latency               (GstClockTime latency);

Create a new latency event. The event is sent upstream from the sinks and notifies elements that they should add an additional latency to the running time before synchronising against the clock.

The latency is mostly used in live sinks and is always expressed in the time format.

latency :

the new latency value

Returns :

a new GstEvent. [transfer full]

Since 0.10.12


gst_event_parse_latency ()

void                gst_event_parse_latency             (GstEvent *event,
                                                         GstClockTime *latency);

Get the latency in the latency event.

event :

The event to query

latency :

A pointer to store the latency in. [out]

Since 0.10.12


gst_event_new_step ()

GstEvent *          gst_event_new_step                  (GstFormat format,
                                                         guint64 amount,
                                                         gdouble rate,
                                                         gboolean flush,
                                                         gboolean intermediate);

Create a new step event. The purpose of the step event is to instruct a sink to skip amount (expressed in format) of media. It can be used to implement stepping through the video frame by frame or for doing fast trick modes.

A rate of <= 0.0 is not allowed. Pause the pipeline, for the effect of rate = 0.0 or first reverse the direction of playback using a seek event to get the same effect as rate < 0.0.

The flush flag will clear any pending data in the pipeline before starting the step operation.

The intermediate flag instructs the pipeline that this step operation is part of a larger step operation.

format :

the format of amount

amount :

the amount of data to step

rate :

the step rate

flush :

flushing steps

intermediate :

intermediate steps

Returns :

a new GstEvent. [transfer full]

Since 0.10.24


gst_event_parse_step ()

void                gst_event_parse_step                (GstEvent *event,
                                                         GstFormat *format,
                                                         guint64 *amount,
                                                         gdouble *rate,
                                                         gboolean *flush,
                                                         gboolean *intermediate);

Parse the step event.

event :

The event to query

format :

a pointer to store the format in. [out][allow-none]

amount :

a pointer to store the amount in. [out][allow-none]

rate :

a pointer to store the rate in. [out][allow-none]

flush :

a pointer to store the flush boolean in. [out][allow-none]

intermediate :

a pointer to store the intermediate boolean in. [out][allow-none]

Since 0.10.24


gst_event_new_sink_message ()

GstEvent *          gst_event_new_sink_message          (GstMessage *msg);

Create a new sink-message event. The purpose of the sink-message event is to instruct a sink to post the message contained in the event synchronized with the stream.

msg :

the GstMessage to be posted. [transfer none]

Returns :

a new GstEvent. [transfer full]

Since 0.10.26


gst_event_parse_sink_message ()

void                gst_event_parse_sink_message        (GstEvent *event,
                                                         GstMessage **msg);

Parse the sink-message event. Unref msg after usage.

event :

The event to query

msg :

a pointer to store the GstMessage in. [out][transfer full]

Since 0.10.26

See Also

GstPad, GstElement