Event

Object Hierarchy:

Description:

public class Event : MiniObject

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 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 Event.seek is used to create a seek event. It takes the needed parameters to specity seeking time and mode.

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 2006-09-6 (0.10.10)

Namespace: Gst

Package: gstreamer-0.10

Content:

Static methods:

public static void replace (ref Event? oldobj, Event? newobj)
public static EventTypeFlags type_get_flags (EventType type)
public static unowned string type_get_name (EventType type)
public static Quark type_to_quark (EventType type)

Creation methods:

public Event.buffer_size (Format format, int64 minsize, int64 maxsize, bool 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.
public Event.custom (EventType type, owned Structure 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.
public Event.eos ()
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 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 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.
public Event.flush_start ()
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 WRONG_STATE when used for data flow with push, chain, alloc_buffer, get_range and pull_range. Any event (except a 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.
public Event.flush_stop ()
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.
public Event.latency (ClockTime 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.
public Event.navigation (owned Structure structure)
Create a new navigation event from the given description.
public Event.new_segment (bool update, double rate, Format format, int64 start, int64 stop, int64 position)
Allocate a new newsegment event with the given format/values tripplets This method calls Event.new_segment_full passing a default value of 1.0 for applied_rate
public Event.new_segment_full (bool update, double rate, double applied_rate, Format format, int64 start, int64 stop, int64 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. 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)
public Event.qos (double proportion, ClockTimeDiff diff, ClockTime timestamp)
Allocate a new qos event with the given values. This function calls Event.qos_full with the type set to OVERFLOW when diff is negative (buffers are in time) and UNDERFLOW when diff is positive (buffers are late).
public Event.qos_full (QOSType type, double proportion, ClockTimeDiff diff, ClockTime 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. used when a buffer arrived in time or when the sink cannot keep up with the upstream datarate. UNDERFLOW is when the sink is not receiving buffers fast enough and thus has to drop late buffers. THROTTLE is used when the datarate is artificially limited by the application, for example to reduce power consumption. 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. 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. 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.
public Event.seek (double rate, Format format, SeekFlags flags, SeekType start_type, int64 start, SeekType stop_type, int64 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 SEGMENT. start and stop fields in playback segment. Adjustments can be made relative or absolute to the last configured values. A type of 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 POSITION and update the playback segment current position with a SET to the desired position.
public Event.sink_message (owned Message 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.
public Event.step (Format format, uint64 amount, double rate, bool flush, bool 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.
public Event.tag (owned TagList taglist)
Generates a metadata tag event from the given taglist.

Methods:

public Event copy ()
public uint32 get_seqnum ()
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 not have the same sequence number unless that correspondence was made explicitly. MT safe.
public unowned Structure get_structure ()
Access the structure of the event. 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.
public bool has_name (string name)
Checks if event has the given name. This function is usually used to check the name of a custom event.
public bool is_downstream ()
public bool is_serialized ()
public bool is_upstream ()
public void parse_buffer_size (out Format format, out int64 minsize, out int64 maxsize, out bool async)
Get the format, minsize, maxsize and async-flag in the buffersize event.
public void parse_latency (out ClockTime latency)
Get the latency in the latency event.
public void parse_new_segment (out bool update, out double rate, out Format format, out int64 start, out int64 stop, out int64 position)
Get the update flag, rate, format, start, stop and position in the newsegment event. In general, parse_new_segment_full should be used instead of this, to also retrieve the applied_rate value of the segment. See Event.new_segment_full for a full description of the newsegment event.
public void parse_new_segment_full (out bool update, out double rate, out double applied_rate, out Format format, out int64 start, out int64 stop, out int64 position)
Get the update, rate, applied_rate, format, start, stop and position in the newsegment event. See Event.new_segment_full for a full description of the newsegment event.
public void parse_qos (out double proportion, out ClockTimeDiff diff, out ClockTime timestamp)
Get the proportion, diff and timestamp in the qos event. See Event.qos for more information about the different QoS values.
public void parse_qos_full (out QOSType type, out double proportion, out ClockTimeDiff diff, out ClockTime timestamp)
Get the type, proportion, diff and timestamp in the qos event. See Event.qos_full for more information about the different QoS values.
public void parse_seek (out double rate, out Format format, out SeekFlags flags, out SeekType start_type, out int64 start, out SeekType stop_type, out int64 stop)
Parses a seek event and stores the results in the given result locations.
public void parse_sink_message (out Message msg)
Parse the sink-message event. Unref msg after usage.
public void parse_step (out Format format, out uint64 amount, out double rate, out bool flush, out bool intermediate)
Parse the step event.
public void parse_tag (out TagList 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.
public weak Event ref ()
public void set_seqnum (uint32 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 get_seqnum for more information. MT safe.
public void unref ()

Fields:

public weak Object src
public uint64 timestamp
public EventType type