Sets our main struct and passes it to the parent class
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.
Allocate a new flush stop event. The flush stop event can be sent upstream and downstream and travels serialized with the dataflow. It is typically sent after sending a FLUSH_START event to make the pads accept data again. Elements can process this event synchronized with the dataflow since the preceeding FLUSH_START event stopped the dataflow. This event is typically generated to complete a seek and to resume dataflow.
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.
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.
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
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.
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.
Allocate a new qos event with the given values. The QOS event is generated in an element that wants an upstream element to either reduce or increase its rate because of high/low CPU load or other resource usage such as network performance or throttling. Typically sinks generate these events for each buffer they receive. type indicates the reason for the QoS event. GST_QOS_TYPE_OVERFLOW is used when a buffer arrived in time or when the sink cannot keep up with the upstream datarate. GST_QOS_TYPE_UNDERFLOW is when the sink is not receiving buffers fast enough and thus has to drop late buffers. GST_QOS_TYPE_THROTTLE is used when the datarate is artificially limited by the application, for example to reduce power consumption. proportion indicates the real-time performance of the streaming in the element that generated the QoS event (usually the sink). The value is generally computed based on more long term statistics about the streams timestamps compared to the clock. A value < 1.0 indicates that the upstream element is producing data faster than real-time. A value > 1.0 indicates that the upstream element is not producing data fast enough. 1.0 is the ideal proportion value. The proportion value can safely be used to lower or increase the quality of the element. diff is the difference against the clock in running time of the last buffer that caused the element to generate the QOS event. A negative value means that the buffer with timestamp arrived in time. A positive value indicates how late the buffer with timestamp was. When throttling is enabled, diff will be set to the requested throttling interval. timestamp is the timestamp of the last buffer that cause the element to generate the QOS event. It is expressed in running time and thus an ever increasing value. The upstream element can use the diff and timestamp values to decide whether to process more buffers. For possitive diff, all buffers with timestamp <= timestamp + diff will certainly arrive late in the sink as well. A (negative) diff value so that timestamp + diff would yield a result smaller than 0 is not allowed. The application can use general event probes to intercept the QoS event and implement custom application specific QoS handling.
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.
Create a new navigation event from the given description.
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.
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.
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.
Create a new reconfigure event. The purpose of the reconfingure 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.
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.
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.
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.
Copy the event using the event specific copy function.
Parses a segment event and copies the GstSegment into the location given by segment.
Increase the refcount of this 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.
the main Gtk struct as a void*
Access the structure of the event.
Checks if event has the given name. This function is usually used to check the name of a custom event.
Get the format, minsize, maxsize and async-flag in the buffersize event.
Get the caps from event. The caps remains valid as long as event remains valid.
Parse the FLUSH_STOP event and retrieve the reset_time member.
Extract timestamp and duration from a new GAP event.
Since 1.2
Get the latency in the latency event.
Get the type, proportion, diff and timestamp in the qos event. See gst_event_new_qos() for more information about the different QoS values.
Parses a seek event and stores the results in the given result locations.
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.
Extracts the position and format from the segment done message.
Parse the sink-message event. Unref msg after usage.
Parse the step event.
Since 1.2
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.
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 a TOC event and store the results in the given toc and updated locations.
Parse a TOC select event and store the results in the given uid location.
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. Since 1.2
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 1.2
Decrease the refcount of an event, freeing it if the refcount reaches 0.
Get a writable version of the structure.
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.
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.
Atomically replace the GstEvent pointed to by old_event with NULL and return the original 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.
Gets the GstEventTypeFlags associated with type.
Get a printable name for the given event type. Do not modify or free.
Get the unique quark for the given event type.
the main Gtk struct
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.
Last reviewed on 2012-03-28 (0.11.3)