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GStreamer 0.10 Core Reference Manual | ![]() |
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GstEventGstEvent — Structure describing events that are passed up and down a pipeline |
#include <gst/gst.h> GstEvent; enum GstEventType; #define GST_EVENT_TRACE_NAME #define GST_EVENT_TYPE (event) #define GST_EVENT_TYPE_NAME (event) #define GST_EVENT_TYPE_BOTH #define GST_EVENT_TIMESTAMP (event) #define GST_EVENT_SRC (event) #define GST_EVENT_IS_DOWNSTREAM (ev) #define GST_EVENT_IS_SERIALIZED (ev) #define GST_EVENT_IS_UPSTREAM (ev) enum GstSeekType; enum GstSeekFlags; enum GstEventTypeFlags; #define GST_EVENT_MAKE_TYPE (num,flags) #define gst_event_copy (ev) const GstStructure* gst_event_get_structure (GstEvent *event); GstEvent* gst_event_new_buffer_size (GstFormat format, gint64 minsize, gint64 maxsize, gboolean async); GstEvent* gst_event_new_custom (GstEventType type, GstStructure *structure); GstEvent* gst_event_new_eos (void); GstEvent* gst_event_new_flush_start (void); GstEvent* gst_event_new_flush_stop (void); GstEvent* gst_event_new_navigation (GstStructure *structure); GstEvent* gst_event_new_new_segment (gboolean update, gdouble rate, GstFormat format, gint64 start, gint64 stop, gint64 position); GstEvent* gst_event_new_qos (gdouble proportion, GstClockTimeDiff diff, GstClockTime timestamp); GstEvent* gst_event_new_seek (gdouble rate, GstFormat format, GstSeekFlags flags, GstSeekType cur_type, gint64 cur, GstSeekType stop_type, gint64 stop); GstEvent* gst_event_new_tag (GstTagList *taglist); void gst_event_parse_buffer_size (GstEvent *event, GstFormat *format, gint64 *minsize, gint64 *maxsize, gboolean *async); void gst_event_parse_new_segment (GstEvent *event, gboolean *update, gdouble *rate, GstFormat *format, gint64 *start, gint64 *stop, gint64 *position); void gst_event_parse_qos (GstEvent *event, gdouble *proportion, GstClockTimeDiff *diff, GstClockTime *timestamp); void gst_event_parse_seek (GstEvent *event, gdouble *rate, GstFormat *format, GstSeekFlags *flags, GstSeekType *cur_type, gint64 *cur, GstSeekType *stop_type, gint64 *stop); void gst_event_parse_tag (GstEvent *event, GstTagList **taglist); #define gst_event_ref (ev) #define gst_event_unref (ev) #define gst_event_replace (old_event,new_event) 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);
The event class provides factory methods to construct and functions query (parse) 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.
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 specity seeking time and mode.
Example 8. performing a seek on a pipeline
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 2006-01-24 (0.10.2)
typedef struct { GstMiniObject mini_object; GstEventType type; guint64 timestamp; GstObject *src; GstStructure *structure; } GstEvent;
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. |
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)), /* 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)), /* 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 |
GST_EVENT_FLUSH_STOP |
Stop a flush operation |
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. |
GST_EVENT_TAG |
A new set of metadata tags has been found in the stream. |
GST_EVENT_BUFFERSIZE |
Notification of buffering requirements |
GST_EVENT_QOS |
A quality message. Used to indicate to upstream elements that the downstream elements are being starved of or flooded with data. |
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_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. |
#define GST_EVENT_TRACE_NAME "GstEvent"
The name used for memory allocation tracing
#define GST_EVENT_TYPE(event) (GST_EVENT_CAST(event)->type)
Get the GstEventType of the event.
event : |
the event to query |
#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 |
#define GST_EVENT_TYPE_BOTH
The same thing as GST_EVENT_TYPE_UPSTREAM | GST_EVENT_TYPE_DOWNSTREAM.
#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 |
#define GST_EVENT_SRC(event) (GST_EVENT_CAST(event)->src)
The source GstObject that generated this event.
event : |
the event to query |
#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 |
#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 |
#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 |
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, 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 current position |
GST_SEEK_TYPE_SET |
absolute position is requested |
GST_SEEK_TYPE_END |
relative position to duration is requested |
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) } GstSeekFlags;
Flags to be used with gst_element_seek()
or gst_event_new_seek()
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 perfoming a segment seek: after the playback of the segment completes, no EOS will be emmited by the element that performed the seek, but a 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 seemless looping or simple linear editing.
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. |
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. |
#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 |
#define gst_event_copy(ev) GST_EVENT_CAST (gst_mini_object_copy (GST_MINI_OBJECT (ev)))
Copy the event using the event specific copy function.
ev : |
The event to copy |
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. |
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 prefered.
format : |
buffer format |
minsize : |
minimum buffer size |
maxsize : |
maximum buffer size |
async : |
thread behavior |
Returns : | a new GstEvent |
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. |
Returns : | The new custom event. |
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 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, the EOS message is forwarded to the application.
Returns : | The new EOS event. |
GstEvent* gst_event_new_flush_start (void);
Allocate a new flush start event. The flush start event can be send upstream and downstream and travels out-of-bounds with the dataflow. It marks pads as being in a WRONG_STATE to process more data.
Elements unlock and blocking functions and exit their streaming functions as fast as possible.
This event is typically generated after a seek to minimize the latency after the seek.
Returns : | A new flush start event. |
GstEvent* gst_event_new_flush_stop (void);
Allocate a new flush stop event. The flush start event can be send upstream and downstream and travels out-of-bounds with the dataflow. It is typically send 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. |
GstEvent* gst_event_new_navigation (GstStructure *structure);
Create a new navigation event from the given description.
structure : |
description of the event |
Returns : | a new GstEvent |
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.
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 use more efficient methods of skipping unneeded packets.
The stream time of the segment is used to convert the buffer timestamps
into the stream time again, this is usually done in sinks to report the
current stream_time. stream_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 than start
.
After a newsegment event, the buffer stream time is calculated with:
stream_time + (TIMESTAMP(buf) - start) * ABS (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. |
GstEvent* gst_event_new_qos (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.
proportion is the requested adjustment in datarate, 1.0 is the normal datarate, 0.75 means increase datarate by 75%, 1.5 is 150%. Negative values request a slow down, so -0.75 means a decrease by 75%.
diff is the difference against the clock in stream time of the last buffer that caused the element to generate the QOS event.
timestamp is the timestamp of the last buffer that cause the element to generate the QOS event.
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. |
GstEvent* gst_event_new_seek (gdouble rate, GstFormat format, GstSeekFlags flags, GstSeekType cur_type, gint64 cur, GstSeekType stop_type, gint64 stop);
Allocate a new seek event with the given parameters.
The seek event configures playback of the pipeline from
cur
to stop
at the speed given in rate
, also called a segment.
The cur
and stop
values are expressed in format 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.
cur_type
and stop_type
specify how to adjust the current and stop
time, relative or absolute. A type of GST_SEEK_TYPE_NONE means that
the position should not be updated. The currently configured playback
segment can be queried with GST_QUERY_SEGMENT.
Note that updating the cur
position will actually move the current
playback pointer to that new position. It is not possible to seek
relative to the current playing position, to do this, pause the pipeline,
get the current position and perform 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 |
cur_type : |
The type and flags for the new current position |
cur : |
The value of the new current 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. |
GstEvent* gst_event_new_tag (GstTagList *taglist);
Generates a metadata tag event from the given taglist
.
taglist : |
metadata list |
Returns : | a new GstEvent |
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 |
minsize : |
A pointer to store the minsize in |
maxsize : |
A pointer to store the maxsize in |
async : |
A pointer to store the async-flag in |
void gst_event_parse_new_segment (GstEvent *event, gboolean *update, gdouble *rate, GstFormat *format, gint64 *start, gint64 *stop, gint64 *position);
Get the format, start, stop and position in the newsegment event.
event : |
The event to query |
update : |
A pointer to the update flag of the segment |
rate : |
A pointer to the rate of the segment |
format : |
A pointer to the format of the newsegment values |
start : |
A pointer to store the start value in |
stop : |
A pointer to store the stop value in |
position : |
A pointer to store the stream time in |
void gst_event_parse_qos (GstEvent *event, gdouble *proportion, GstClockTimeDiff *diff, GstClockTime *timestamp);
Get the proportion, diff and timestamp in the qos event.
event : |
The event to query |
proportion : |
A pointer to store the proportion in |
diff : |
A pointer to store the diff in |
timestamp : |
A pointer to store the timestamp in |
void gst_event_parse_seek (GstEvent *event, gdouble *rate, GstFormat *format, GstSeekFlags *flags, GstSeekType *cur_type, gint64 *cur, 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 |
format : |
result location for the stream format |
flags : |
result location for the GstSeekFlags |
cur_type : |
result location for the GstSeekType of the current position |
cur : |
result location for the current postion expressed in format
|
stop_type : |
result location for the GstSeekType of the stop position |
stop : |
result location for the stop postion expressed in format
|
void gst_event_parse_tag (GstEvent *event, GstTagList **taglist);
Parses a tag event
and stores the results in the given taglist
location.
event : |
a tag event |
taglist : |
pointer to metadata list |
#define gst_event_ref(ev) GST_EVENT (gst_mini_object_ref (GST_MINI_OBJECT (ev)))
Increase the refcount of this event.
ev : |
The event to refcount |
#define gst_event_unref(ev) gst_mini_object_unref (GST_MINI_OBJECT (ev))
Decrease the refcount of an event, freeing it if the refcount reaches 0.
ev : |
The event to refcount |
#define gst_event_replace(old_event,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. |
new_event : |
pointer to a GstEvent that will replace the event pointed to
by old_event .
|
Since 0.10.3
GstEventTypeFlags gst_event_type_get_flags (GstEventType type);
Gets the GstEventTypeFlags associated with type
.
type : |
a GstEventType |
Returns : | a GstEventTypeFlags. |
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. |
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 |
<< GstGError | GstFilter >> |