Event#

class Event(*args, **kwargs)#

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 send_event() and elements will use send_event() or 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 None 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 new_seek() is used to create a seek event. It takes the needed parameters to specify seeking time and mode.

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");
...

Constructors#

class Event

classmethod new_buffer_size(format: Format, minsize: int, maxsize: int, async_: bool) → Event#

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

classmethod new_caps(caps: Caps) → Event#

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 Caps

classmethod new_custom(type: EventType, structure: Structure) → Event#

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.

classmethod new_eos() → Event#

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 FlowReturn 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.

classmethod new_flush_start() → Event#

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 push(), chain(), get_range() and 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.

classmethod new_flush_stop(reset_time: bool) → Event#

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

classmethod new_gap(timestamp: int, duration: int) → Event#

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

classmethod new_instant_rate_change(rate_multiplier: float, new_flags: SegmentFlags) → Event#

Create a new instant-rate-change event. This event is sent by seek handlers (e.g. demuxers) when receiving a seek with the INSTANT_RATE_CHANGE and signals to downstream elements that the playback rate in the existing segment should be immediately multiplied by the rate_multiplier factor.

The flags provided replace any flags in the existing segment, for the flags within the SEGMENT_INSTANT_FLAGS set. Other GstSegmentFlags are ignored and not transferred in the event.

Added in version 1.18.

Parameters:

rate_multiplier – the multiplier to be applied to the playback rate
new_flags – A new subset of segment flags to replace in segments

classmethod new_instant_rate_sync_time(rate_multiplier: float, running_time: int, upstream_running_time: int) → Event#

Create a new instant-rate-sync-time event. This event is sent by the pipeline to notify elements handling the instant-rate-change event about the running-time when the new rate should be applied. The running time may be in the past when elements handle this event, which can lead to switching artifacts. The magnitude of those depends on the exact timing of event delivery to each element and the magnitude of the change in playback rate being applied.

The running_time and upstream_running_time are the same if this is the first instant-rate adjustment, but will differ for later ones to compensate for the accumulated offset due to playing at a rate different to the one indicated in the playback segments.

Added in version 1.18.

Parameters:

rate_multiplier – the new playback rate multiplier to be applied
running_time – Running time when the rate change should be applied
upstream_running_time – The upstream-centric running-time when the rate change should be applied.

classmethod new_latency(latency: int) → Event#

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

classmethod new_navigation(structure: Structure) → Event#

Create a new navigation event from the given description.

Parameters:: structure – description of the event. The event will take ownership of the structure. See GstNavigation for more specific constructors.

classmethod new_protection(system_id: str, data: Buffer, origin: str) → Event#

Creates a new event containing information specific to a particular protection system (uniquely identified by system_id), by which that protection system can acquire key(s) to decrypt a protected stream.

In order for a decryption element to decrypt media protected using a specific system, it first needs all the protection system specific information necessary to acquire the decryption key(s) for that stream. The functions defined here enable this information to be passed in events from elements that extract it (e.g., ISOBMFF demuxers, MPEG DASH demuxers) to protection decrypter elements that use it.

Events containing protection system specific information are created using gst_event_new_protection, and they can be parsed by downstream elements using gst_event_parse_protection.

In Common Encryption, protection system specific information may be located within ISOBMFF files, both in movie (moov) boxes and movie fragment (moof) boxes; it may also be contained in ContentProtection elements within MPEG DASH MPDs. The events created by gst_event_new_protection contain data identifying from which of these locations the encapsulated protection system specific information originated. This origin information is required as some protection systems use different encodings depending upon where the information originates.

The events returned by new_protection() are implemented in such a way as to ensure that the most recently-pushed protection info event of a particular origin and system_id will be stuck to the output pad of the sending element.

Added in version 1.6.

Parameters:

system_id – a string holding a UUID that uniquely identifies a protection system.
data – a Buffer holding protection system specific information. The reference count of the buffer will be incremented by one.
origin – a string indicating where the protection information carried in the event was extracted from. The allowed values of this string will depend upon the protection scheme.

classmethod new_qos(type: QOSType, proportion: float, diff: int, timestamp: int) → Event#

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

classmethod new_reconfigure() → Event#: 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.

classmethod new_seek(rate: float, format: Format, flags: SeekFlags, start_type: SeekType, start: int, stop_type: SeekType, stop: int) → Event#

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

classmethod new_segment(segment: Segment) → Event#

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 segment 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 segment event with rate of 1.0 and applied_rate of 2.0

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

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

Parameters:: segment – a Segment

classmethod new_segment_done(format: Format, position: int) → Event#

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

classmethod new_select_streams(streams: list[str]) → Event#

Allocate a new select-streams event.

The select-streams event requests the specified streams to be activated.

The list of streams corresponds to the “Stream ID” of each stream to be activated. Those ID can be obtained via the Stream objects present in GST_EVENT_STREAM_START, GST_EVENT_STREAM_COLLECTION or GST_MESSAGE_STREAM_COLLECTION.

Note: The list of streams can not be empty.

Added in version 1.10.

Parameters:: streams – the list of streams to activate

classmethod new_sink_message(name: str, msg: Message) → Event#

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 Message to be posted

classmethod new_step(format: Format, amount: int, rate: float, flush: bool, intermediate: bool) → Event#

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

classmethod new_stream_collection(collection: StreamCollection) → Event#

Create a new STREAM_COLLECTION event. The stream collection event can only travel downstream synchronized with the buffer flow.

Source elements, demuxers and other elements that manage collections of streams and post StreamCollection messages on the bus also send this event downstream on each pad involved in the collection, so that activation of a new collection can be tracked through the downstream data flow.

Added in version 1.10.

Parameters:: collection – Active collection for this data flow

classmethod new_stream_group_done(group_id: int) → Event#

Create a new Stream Group Done event. The stream-group-done event can only travel downstream synchronized with the buffer flow. Elements that receive the event on a pad should handle it mostly like EOS, and emit any data or pending buffers that would depend on more data arriving and unblock, since there won’t be any more data.

This event is followed by EOS at some point in the future, and is generally used when switching pads - to unblock downstream so that new pads can be exposed before sending EOS on the existing pads.

Added in version 1.10.

Parameters:: group_id – the group id of the stream group which is ending

classmethod new_stream_start(stream_id: str) → Event#

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 sent 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. create_stream_id() or create_stream_id_printf() can be used to create a stream-id. There are no particular semantics for the stream-id, though it should be deterministic (to support stream matching) and it might be used to order streams (besides any information conveyed by stream flags).

Parameters:: stream_id – Identifier for this stream

classmethod new_tag(taglist: TagList) → Event#

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.

classmethod new_toc(toc: Toc, updated: bool) → Event#

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 – Toc structure.
updated – whether toc was updated or not.

classmethod new_toc_select(uid: str) → Event#

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.

Methods#

class Event

get_running_time_offset() → int#

Retrieve the accumulated running time offset of the event.

Events passing through Pad that have a running time offset set via 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.

Added in version 1.4.

get_seqnum() → int#

Retrieve the sequence number of a event.

Events have ever-incrementing sequence numbers, which may also be set explicitly via 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.

get_structure() → Structure | None#: Access the structure of the event.

has_name(name: str) → bool#

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

Parameters:: name – name to check

has_name_id(name: int) → bool#

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

Added in version 1.18.

Parameters:: name – name to check as a GQuark

parse_buffer_size() → Tuple[Format, int, int, bool]#: Get the format, minsize, maxsize and async-flag in the buffersize event.

parse_caps() → Caps#: Get the caps from event. The caps remains valid as long as event remains valid.

parse_flush_stop() → bool#: Parse the FLUSH_STOP event and retrieve the reset_time member.

parse_gap() → Tuple[int, int]#: Extract timestamp and duration from a new GAP event.

parse_gap_flags() → GapFlags#: Retrieve the gap flags that may have been set on a gap event with set_gap_flags().

Added in version 1.20.

parse_group_id() → Tuple[bool, int]#: Added in version 1.2.

parse_instant_rate_change() → Tuple[float, SegmentFlags]#: Extract rate and flags from an instant-rate-change event.

Added in version 1.18.

parse_instant_rate_sync_time() → Tuple[float, int, int]#: Extract the rate multiplier and running times from an instant-rate-sync-time event.

Added in version 1.18.

parse_latency() → int#: Get the latency in the latency event.

parse_protection() → Tuple[str, Buffer, str]#: Parses an event containing protection system specific information and stores the results in system_id, data and origin. The data stored in system_id, origin and data are valid until event is released.

Added in version 1.6.

parse_qos() → Tuple[QOSType, float, int, int]#

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

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

parse_seek() → Tuple[float, Format, SeekFlags, SeekType, int, SeekType, int]#: Parses a seek event and stores the results in the given result locations.

parse_seek_trickmode_interval() → int#: Retrieve the trickmode interval that may have been set on a seek event with set_seek_trickmode_interval().

Added in version 1.16.

parse_segment() → 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.

parse_segment_done() → Tuple[Format, int]#: Extracts the position and format from the segment done message.

parse_select_streams() → list[str]#: Parse the SELECT_STREAMS event and retrieve the contained streams.

Added in version 1.10.

parse_sink_message() → Message#: Parse the sink-message event. Unref msg after usage.

parse_step() → Tuple[Format, int, float, bool, bool]#: Parse the step event.

parse_stream() → Stream#: Parse a stream-start event and extract the Stream from it.

Added in version 1.10.

parse_stream_collection() → StreamCollection#: Retrieve new StreamCollection from STREAM_COLLECTION event event.

Added in version 1.10.

parse_stream_flags() → StreamFlags#: Added in version 1.2.

parse_stream_group_done() → int#: Parse a stream-group-done event and store the result in the given group_id location.

Added in version 1.10.

parse_stream_start() → str#: 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.

parse_tag() → 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.

parse_toc() → Tuple[Toc, bool]#: Parse a TOC event and store the results in the given toc and updated locations.

parse_toc_select() → str#: Parse a TOC select event and store the results in the given uid location.

set_gap_flags(flags: GapFlags) → None#

Sets flags on event to give additional information about the reason for the GST_EVENT_GAP.

Added in version 1.20.

Parameters:: flags – a GapFlags

set_group_id(group_id: int) → None#

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 util_group_id_next() to get a new group id.

Added in version 1.2.

Parameters:: group_id – the group id to set

set_running_time_offset(offset: int) → None#

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

MT safe.

Added in version 1.4.

Parameters:: offset – A the new running time offset

set_seek_trickmode_interval(interval: int) → None#

Sets a trickmode interval on a (writable) seek event. Elements that support TRICKMODE_KEY_UNITS seeks SHOULD use this as the minimal interval between each frame they may output.

Added in version 1.16.

Parameters:: interval

set_seqnum(seqnum: int) → None#

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 get_seqnum() for more information.

MT safe.

Parameters:: seqnum – A sequence number.

set_stream(stream: Stream) → None#

Set the stream on the stream-start event

Added in version 1.10.

Parameters:: stream – the stream object to set

set_stream_flags(flags: StreamFlags) → None#

Added in version 1.2.

Parameters:: flags – the stream flags to set

writable_structure() → Structure#: Get a writable version of the structure.

Fields#

class Event

mini_object#: The parent structure

seqnum#: The sequence number of the event

timestamp#: The timestamp of the event

type#: The EventType of the event

Event#

Constructors#

Methods#

Fields#

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