GstEvent

typedef struct {
  GstMiniObject mini_object;

  GstEventType  type;
  guint64       timestamp;
  GstObject     *src;

  GstStructure  *structure;
} GstEvent;

A GstEvent.

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_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

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)),
  /* 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_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.

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.

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.

GST_EVENT_SRC()

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

The source GstObject that generated this event.

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.

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.

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.

gst_event_type_get_flags ()

GstEventTypeFlags   gst_event_type_get_flags            (GstEventType type);

Gets the GstEventTypeFlags associated with type.

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.

gst_event_type_to_quark ()

GQuark              gst_event_type_to_quark             (GstEventType type);

Get the unique quark for the given event type.

gst_event_ref ()

GstEvent*           gst_event_ref                       (GstEvent *event);

Increase the refcount of this event.

gst_event_unref ()

void                gst_event_unref                     (GstEvent *event);

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

gst_event_replace()

#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.

Since 0.10.3

gst_event_copy ()

void                gst_event_copy                      (GstEvent *event);

Copy the event using the event specific copy function.

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.

gst_event_get_structure ()

const GstStructure* gst_event_get_structure             (GstEvent *event);

Access the structure of the event.

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.

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 not have the same sequence number unless that correspondence was made explicitly.

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.

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.

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 out-of-bounds 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.

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.

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

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)

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.

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.

Since 0.10.6

gst_event_new_tag ()

GstEvent*           gst_event_new_tag                   (GstTagList *taglist);

Generates a metadata tag event from the given taglist.

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.

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 prefered.

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.

gst_event_new_qos ()

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 or other resource usage such as network performance. Typically sinks generate these events for each buffer they receive.

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.

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.

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.

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().

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 seemless 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.

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.

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.

gst_event_new_navigation ()

GstEvent*           gst_event_new_navigation            (GstStructure *structure);

Create a new navigation event from the given description.

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.

Since 0.10.12

gst_event_parse_latency ()

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

Get the latency in the latency event.

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 or reverse the playback direction of the pipeline to get the same effect.

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.

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.

Since 0.10.24