GstEvent

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

Functions

#define GST_EVENT_MAKE_TYPE()
#define GST_EVENT_TYPE()
#define GST_EVENT_TYPE_NAME()
#define GST_EVENT_TIMESTAMP()
#define GST_EVENT_SEQNUM()
#define GST_EVENT_IS_UPSTREAM()
#define GST_EVENT_IS_DOWNSTREAM()
#define GST_EVENT_IS_SERIALIZED()
#define GST_EVENT_IS_STICKY()
GstEventTypeFlags gst_event_type_get_flags ()
const gchar * gst_event_type_get_name ()
GQuark gst_event_type_to_quark ()
GstEvent * gst_event_ref ()
void gst_event_unref ()
gboolean gst_event_replace ()
GstEvent * gst_event_copy ()
GstEvent * gst_event_steal ()
gboolean gst_event_take ()
#define gst_event_is_writable()
#define gst_event_make_writable()
GstStructure * gst_event_writable_structure ()
GstEvent * gst_event_new_custom ()
const GstStructure * gst_event_get_structure ()
gboolean gst_event_has_name ()
guint32 gst_event_get_seqnum ()
void gst_event_set_seqnum ()
gint64 gst_event_get_running_time_offset ()
void gst_event_set_running_time_offset ()
GstEvent * gst_event_new_flush_start ()
GstEvent * gst_event_new_flush_stop ()
void gst_event_parse_flush_stop ()
GstEvent * gst_event_new_eos ()
GstEvent * gst_event_new_gap ()
void gst_event_parse_gap ()
GstEvent * gst_event_new_stream_start ()
void gst_event_parse_stream_start ()
void gst_event_set_stream_flags ()
void gst_event_parse_stream_flags ()
void gst_event_set_group_id ()
gboolean gst_event_parse_group_id ()
GstEvent * gst_event_new_segment ()
void gst_event_parse_segment ()
void gst_event_copy_segment ()
GstEvent * gst_event_new_tag ()
void gst_event_parse_tag ()
GstEvent * gst_event_new_buffer_size ()
void gst_event_parse_buffer_size ()
GstEvent * gst_event_new_qos ()
void gst_event_parse_qos ()
GstEvent * gst_event_new_seek ()
void gst_event_parse_seek ()
GstEvent * gst_event_new_navigation ()
GstEvent * gst_event_new_latency ()
void gst_event_parse_latency ()
GstEvent * gst_event_new_step ()
void gst_event_parse_step ()
GstEvent * gst_event_new_sink_message ()
void gst_event_parse_sink_message ()
GstEvent * gst_event_new_reconfigure ()
GstEvent * gst_event_new_caps ()
void gst_event_parse_caps ()
GstEvent * gst_event_new_toc ()
void gst_event_parse_toc ()
GstEvent * gst_event_new_toc_select ()
void gst_event_parse_toc_select ()
GstEvent * gst_event_new_segment_done ()
void gst_event_parse_segment_done ()

Types and Values

Object Hierarchy

    GBoxed
    ╰── GstEvent

Includes

#include <gst/gst.h>

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.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
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");
...

Functions

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

Parameters

num

the event number to create

 

flags

the event flags

 

GST_EVENT_TYPE()

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

Get the GstEventType of the event.

Parameters

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.

Parameters

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.

Parameters

event

the event to query

 

GST_EVENT_SEQNUM()

#define GST_EVENT_SEQNUM(event)         (GST_EVENT_CAST(event)->seqnum)

The sequence number of event .

Parameters

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.

Parameters

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.

Parameters

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.

Parameters

ev

the event to query

 

GST_EVENT_IS_STICKY()

#define GST_EVENT_IS_STICKY(ev)     !!(GST_EVENT_TYPE (ev) & GST_EVENT_TYPE_STICKY)

Check if an event is sticky on the pads.

Parameters

ev

the event to query

 

gst_event_type_get_flags ()

GstEventTypeFlags
gst_event_type_get_flags (GstEventType type);

Gets the GstEventTypeFlags associated with type .

Parameters

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.

Parameters

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.

Parameters

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.

Parameters

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.

Parameters

event

the event to refcount.

[transfer full]

gst_event_replace ()

gboolean
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.

Parameters

old_event

pointer to a pointer to a GstEvent to be replaced.

[inout][transfer full][nullable]

new_event

pointer to a GstEvent that will replace the event pointed to by old_event .

[allow-none][transfer none]

Returns

TRUE if new_event was different from old_event


gst_event_copy ()

GstEvent *
gst_event_copy (const GstEvent *event);

Copy the event using the event specific copy function.

Parameters

event

The event to copy

 

Returns

the new event.

[transfer full]


gst_event_steal ()

GstEvent *
gst_event_steal (GstEvent **old_event);

Atomically replace the GstEvent pointed to by old_event with NULL and return the original event.

Parameters

old_event

pointer to a pointer to a GstEvent to be stolen.

[inout][transfer full][nullable]

Returns

the GstEvent that was in old_event


gst_event_take ()

gboolean
gst_event_take (GstEvent **old_event,
                GstEvent *new_event);

Modifies a pointer to a GstEvent to point to a different GstEvent. This function is similar to gst_event_replace() except that it takes ownership of new_event .

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

Parameters

old_event

pointer to a pointer to a GstEvent to be stolen.

[inout][transfer full][nullable]

new_event

pointer to a GstEvent that will replace the event pointed to by old_event .

[allow-none][transfer full]

Returns

TRUE if new_event was different from old_event


gst_event_is_writable()

#define         gst_event_is_writable(ev)     gst_mini_object_is_writable (GST_MINI_OBJECT_CAST (ev))

Tests if you can safely write data into a event's structure or validly modify the seqnum and timestamp field.

Parameters

ev

a GstEvent

 

gst_event_make_writable()

#define         gst_event_make_writable(ev)   GST_EVENT_CAST (gst_mini_object_make_writable (GST_MINI_OBJECT_CAST (ev)))

Makes a writable event from the given event. If the source event is already writable, this will simply return the same event. A copy will otherwise be made using gst_event_copy().

Parameters

ev

a GstEvent.

[transfer full]

Returns

a writable event which may or may not be the same as ev .

[transfer full]


gst_event_writable_structure ()

GstStructure *
gst_event_writable_structure (GstEvent *event);

Get a writable version of the structure.

Parameters

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. This function checks if event is writable and will never return NULL.

MT safe.

[transfer none]


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.

Parameters

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.

Parameters

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.

Parameters

event

The GstEvent.

 

name

name to check

 

Returns

TRUE if name matches the name of the event structure.


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.

Parameters

event

A GstEvent.

 

Returns

The event's sequence number.

MT safe.


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.

Parameters

event

A GstEvent.

 

seqnum

A sequence number.

 

gst_event_get_running_time_offset ()

gint64
gst_event_get_running_time_offset (GstEvent *event);

Retrieve the accumulated running time offset of the event.

Events passing through GstPads that have a running time offset set via gst_pad_set_offset() will get their offset adjusted according to the pad's offset.

If the event contains any information that related to the running time, this information will need to be updated before usage with this offset.

Parameters

event

A GstEvent.

 

Returns

The event's running time offset

MT safe.

Since 1.4


gst_event_set_running_time_offset ()

void
gst_event_set_running_time_offset (GstEvent *event,
                                   gint64 offset);

Set the running time offset of a event. See gst_event_get_running_time_offset() for more information.

MT safe.

Parameters

event

A GstEvent.

 

offset

A the new running time offset

 

Since 1.4


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_FLUSHING when used for data flow with gst_pad_push(), gst_pad_chain(), 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 (gboolean reset_time);

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 preceding FLUSH_START event stopped the dataflow.

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

Parameters

reset_time

if time should be reset

 

Returns

a new flush stop event.

[transfer full]


gst_event_parse_flush_stop ()

void
gst_event_parse_flush_stop (GstEvent *event,
                            gboolean *reset_time);

Parse the FLUSH_STOP event and retrieve the reset_time member.

Parameters

event

The event to parse

 

reset_time

if time should be reset.

[out]

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_EOS 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_gap ()

GstEvent *
gst_event_new_gap (GstClockTime timestamp,
                   GstClockTime duration);

Create a new GAP event. A gap event can be thought of as conceptually equivalent to a buffer to signal that there is no data for a certain amount of time. This is useful to signal a gap to downstream elements which may wait for data, such as muxers or mixers or overlays, especially for sparse streams such as subtitle streams.

Parameters

timestamp

the start time (pts) of the gap

 

duration

the duration of the gap

 

Returns

the new GAP event.

[transfer full]


gst_event_parse_gap ()

void
gst_event_parse_gap (GstEvent *event,
                     GstClockTime *timestamp,
                     GstClockTime *duration);

Extract timestamp and duration from a new GAP event.

Parameters

event

a GstEvent of type GST_EVENT_GAP

 

timestamp

location where to store the start time (pts) of the gap, or NULL.

[out][allow-none]

duration

location where to store the duration of the gap, or NULL.

[out][allow-none]

gst_event_new_stream_start ()

GstEvent *
gst_event_new_stream_start (const gchar *stream_id);

Create a new STREAM_START event. The stream start event can only travel downstream synchronized with the buffer flow. It is expected to be the first event that is sent for a new stream.

Source elements, demuxers and other elements that create new streams are supposed to send this event as the first event of a new stream. It should not be send after a flushing seek or in similar situations and is used to mark the beginning of a new logical stream. Elements combining multiple streams must ensure that this event is only forwarded downstream once and not for every single input stream.

The stream_id should be a unique string that consists of the upstream stream-id, / as separator and a unique stream-id for this specific stream. A new stream-id should only be created for a stream if the upstream stream is split into (potentially) multiple new streams, e.g. in a demuxer, but not for every single element in the pipeline. gst_pad_create_stream_id() or gst_pad_create_stream_id_printf() can be used to create a stream-id.

Parameters

stream_id

Identifier for this stream

 

Returns

the new STREAM_START event.

[transfer full]


gst_event_parse_stream_start ()

void
gst_event_parse_stream_start (GstEvent *event,
                              const gchar **stream_id);

Parse a stream-id event and store the result in the given stream_id location. The string stored in stream_id must not be modified and will remain valid only until event gets freed. Make a copy if you want to modify it or store it for later use.

Parameters

event

a stream-start event.

 

stream_id

pointer to store the stream-id.

[out][transfer none]

gst_event_set_stream_flags ()

void
gst_event_set_stream_flags (GstEvent *event,
                            GstStreamFlags flags);

Parameters

event

a stream-start event

 

flags

the stream flags to set

 

Since 1.2


gst_event_parse_stream_flags ()

void
gst_event_parse_stream_flags (GstEvent *event,
                              GstStreamFlags *flags);

Parameters

event

a stream-start event

 

flags

address of variable where to store the stream flags.

[out]

Since 1.2


gst_event_set_group_id ()

void
gst_event_set_group_id (GstEvent *event,
                        guint group_id);

All streams that have the same group id are supposed to be played together, i.e. all streams inside a container file should have the same group id but different stream ids. The group id should change each time the stream is started, resulting in different group ids each time a file is played for example.

Use gst_util_group_id_next() to get a new group id.

Parameters

event

a stream-start event

 

group_id

the group id to set

 

Since 1.2


gst_event_parse_group_id ()

gboolean
gst_event_parse_group_id (GstEvent *event,
                          guint *group_id);

Parameters

event

a stream-start event

 

group_id

address of variable where to store the group id.

[out]

Returns

TRUE if a group id was set on the event and could be parsed, FALSE otherwise.

Since 1.2


gst_event_new_segment ()

GstEvent *
gst_event_new_segment (const GstSegment *segment);

Create a new SEGMENT event for segment . The segment event can only travel downstream synchronized with the buffer flow and contains timing information and playback properties for the buffers that will follow.

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 time 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. time represents the stream_time of a buffer carrying a timestamp of start . time 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:

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

Parameters

segment

a GstSegment.

[transfer none]

Returns

the new SEGMENT event.

[transfer full]


gst_event_parse_segment ()

void
gst_event_parse_segment (GstEvent *event,
                         const GstSegment **segment);

Parses a segment event and stores the result in the given segment location. segment remains valid only until the event is freed. Don't modify the segment and make a copy if you want to modify it or store it for later use.

Parameters

event

The event to parse

 

segment

a pointer to a GstSegment.

[out][transfer none]

gst_event_copy_segment ()

void
gst_event_copy_segment (GstEvent *event,
                        GstSegment *segment);

Parses a segment event and copies the GstSegment into the location given by segment .

Parameters

event

The event to parse

 

segment

a pointer to a GstSegment

 

gst_event_new_tag ()

GstEvent *
gst_event_new_tag (GstTagList *taglist);

Generates a metadata tag event from the given taglist .

The scope of the taglist specifies if the taglist applies to the complete medium or only to this specific stream. As the tag event is a sticky event, elements should merge tags received from upstream with a given scope with their own tags with the same scope and create a new tag event from it.

Parameters

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.

Parameters

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.

Parameters

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.

Parameters

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]

gst_event_new_qos ()

GstEvent *
gst_event_new_qos (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 positive 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.

Parameters

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]


gst_event_parse_qos ()

void
gst_event_parse_qos (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() for more information about the different QoS values.

timestamp will be adjusted for any pad offsets of pads it was passing through.

Parameters

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]

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 is updated, it must be different from -1 (GST_CLOCK_TIME_NONE) 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.

Parameters

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.

Parameters

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 position expressed in format .

[out]

stop_type

result location for the GstSeekType of the stop position.

[out]

stop

result location for the stop position expressed in format .

[out]

gst_event_new_navigation ()

GstEvent *
gst_event_new_navigation (GstStructure *structure);

Create a new navigation event from the given description.

Parameters

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.

Parameters

latency

the new latency value

 

Returns

a new GstEvent.

[transfer full]


gst_event_parse_latency ()

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

Get the latency in the latency event.

Parameters

event

The event to query

 

latency

A pointer to store the latency in.

[out]

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.

Parameters

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]


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.

Parameters

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]

gst_event_new_sink_message ()

GstEvent *
gst_event_new_sink_message (const gchar *name,
                            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.

name is used to store multiple sticky events on one pad.

Parameters

name

a name for the event

 

msg

the GstMessage to be posted.

[transfer none]

Returns

a new GstEvent.

[transfer full]


gst_event_parse_sink_message ()

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

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

Parameters

event

The event to query

 

msg

a pointer to store the GstMessage in.

[out][transfer full]

gst_event_new_reconfigure ()

GstEvent *
gst_event_new_reconfigure (void);

Create a new reconfigure event. The purpose of the reconfigure event is to travel upstream and make elements renegotiate their caps or reconfigure their buffer pools. This is useful when changing properties on elements or changing the topology of the pipeline.

Returns

a new GstEvent.

[transfer full]


gst_event_new_caps ()

GstEvent *
gst_event_new_caps (GstCaps *caps);

Create a new CAPS event for caps . The caps event can only travel downstream synchronized with the buffer flow and contains the format of the buffers that will follow after the event.

Parameters

caps

a GstCaps.

[transfer none]

Returns

the new CAPS event.

[transfer full]


gst_event_parse_caps ()

void
gst_event_parse_caps (GstEvent *event,
                      GstCaps **caps);

Get the caps from event . The caps remains valid as long as event remains valid.

Parameters

event

The event to parse

 

caps

A pointer to the caps.

[out][transfer none]

gst_event_new_toc ()

GstEvent *
gst_event_new_toc (GstToc *toc,
                   gboolean updated);

Generate a TOC event from the given toc . The purpose of the TOC event is to inform elements that some kind of the TOC was found.

Parameters

toc

GstToc structure.

[transfer none]

updated

whether toc was updated or not.

 

Returns

a new GstEvent.

[transfer full]


gst_event_parse_toc ()

void
gst_event_parse_toc (GstEvent *event,
                     GstToc **toc,
                     gboolean *updated);

Parse a TOC event and store the results in the given toc and updated locations.

Parameters

event

a TOC event.

 

toc

pointer to GstToc structure.

[out][transfer full]

updated

pointer to store TOC updated flag.

[out]

gst_event_new_toc_select ()

GstEvent *
gst_event_new_toc_select (const gchar *uid);

Generate a TOC select event with the given uid . The purpose of the TOC select event is to start playback based on the TOC's entry with the given uid .

Parameters

uid

UID in the TOC to start playback from.

 

Returns

a new GstEvent.


gst_event_parse_toc_select ()

void
gst_event_parse_toc_select (GstEvent *event,
                            gchar **uid);

Parse a TOC select event and store the results in the given uid location.

Parameters

event

a TOC select event.

 

uid

storage for the selection UID.

[out][transfer full][allow-none]

gst_event_new_segment_done ()

GstEvent *
gst_event_new_segment_done (GstFormat format,
                            gint64 position);

Create a new segment-done event. This event is sent by elements that finish playback of a segment as a result of a segment seek.

Parameters

format

The format of the position being done

 

position

The position of the segment being done

 

Returns

a new GstEvent.

[transfer full]


gst_event_parse_segment_done ()

void
gst_event_parse_segment_done (GstEvent *event,
                              GstFormat *format,
                              gint64 *position);

Extracts the position and format from the segment done message.

Parameters

event

A valid GstEvent of type GST_EVENT_SEGMENT_DONE.

 

format

Result location for the format, or NULL.

[out][allow-none]

position

Result location for the position, or NULL.

[out][allow-none]

Types and Values

struct GstEvent

struct GstEvent {
  GstMiniObject mini_object;

  GstEventType  type;
  guint64       timestamp;
  guint32       seqnum;
};

A GstEvent.

Members

GstMiniObject mini_object;

the parent structure

 

GstEventType type;

the GstEventType of the event

 

guint64 timestamp;

the timestamp of the event

 

guint32 seqnum;

the sequence number of the event

 

enum 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.

Members

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_STICKY

Set if the event is sticky on the pads.

 

GST_EVENT_TYPE_STICKY_MULTI

Multiple sticky events can be on a pad, each identified by the event name.

 

GST_EVENT_TYPE_BOTH

#define             GST_EVENT_TYPE_BOTH

The same thing as GST_EVENT_TYPE_UPSTREAM | GST_EVENT_TYPE_DOWNSTREAM.


enum 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.

Members

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_STREAM_START

Event to mark the start of a new stream. Sent before any other serialized event and only sent at the start of a new stream, not after flushing seeks.

 

GST_EVENT_CAPS

GstCaps event. Notify the pad of a new media type.

 

GST_EVENT_SEGMENT

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.

 

GST_EVENT_EOS

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

 

GST_EVENT_TOC

An event which indicates that a new table of contents (TOC) was found or updated.

 

GST_EVENT_SEGMENT_DONE

Marks the end of a segment playback.

 

GST_EVENT_GAP

Marks a gap in the datastream.

 

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.

 

GST_EVENT_STEP

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

 

GST_EVENT_RECONFIGURE

A request for upstream renegotiating caps and reconfiguring.

 

GST_EVENT_TOC_SELECT

A request for a new playback position based on TOC entry's UID.

 

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_DOWNSTREAM_STICKY

Custom sticky 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.

 

enum GstStreamFlags

Members

GST_STREAM_FLAG_NONE

This stream has no special attributes

 

GST_STREAM_FLAG_SPARSE

This stream is a sparse stream (e.g. a subtitle stream), data may flow only in irregular intervals with large gaps in between.

 

GST_STREAM_FLAG_SELECT

This stream should be selected by default. This flag may be used by demuxers to signal that a stream should be selected by default in a playback scenario.

 

GST_STREAM_FLAG_UNSELECT

This stream should not be selected by default. This flag may be used by demuxers to signal that a stream should not be selected by default in a playback scenario, but only if explicitly selected by the user (e.g. an audio track for the hard of hearing or a director's commentary track).

 

Since 1.2


enum GstQOSType

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

Members

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.

 

enum GstSeekType

The different types of seek events. When constructing a seek event with gst_event_new_seek() or when doing gst_segment_do_seek().

Members

GST_SEEK_TYPE_NONE

no change in position is required

 

GST_SEEK_TYPE_SET

absolute position is requested

 

GST_SEEK_TYPE_END

relative position to duration is requested

 

enum 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 emitted 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.

The GST_SEEK_FLAG_SNAP_BEFORE flag can be used to snap to the previous relevant location, and the GST_SEEK_FLAG_SNAP_AFTER flag can be used to select the next relevant location. If KEY_UNIT is specified, the relevant location is a keyframe. If both flags are specified, the nearest of these locations will be selected. If none are specified, the implementation is free to select whichever it wants. The before and after here are in running time, so when playing backwards, the next location refers to the one that will played in next, and not the one that is located after in the actual source stream.

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.

Members

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 forward or fast reverse playback, allow elements to skip frames instead of generating all frames.

 

GST_SEEK_FLAG_SNAP_BEFORE

go to a location before the requested position, if KEY_UNIT this means the keyframe at or before the requested position the one at or before the seek target.

 

GST_SEEK_FLAG_SNAP_AFTER

go to a location after the requested position, if KEY_UNIT this means the keyframe at of after the requested position.

 

GST_SEEK_FLAG_SNAP_NEAREST

go to a position near the requested position, if KEY_UNIT this means the keyframe closest to the requested position, if both keyframes are at an equal distance, behaves like SNAP_BEFORE.

 

See Also

GstPad, GstElement