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

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_SEQNUM()

#define GST_EVENT_SEQNUM(event)         (GST_EVENT_CAST(event)->seqnum)

The sequence number of 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_IS_STICKY()

#define GST_EVENT_IS_STICKY(ev)     !!(GST_EVENT_TYPE (ev) & GST_EVENT_TYPE_STICKY)

Check if an event is sticky on the pads.

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 ()

gboolean
gst_event_replace (GstEvent **old_event,
                   GstEvent *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.

gst_event_copy ()

GstEvent *
gst_event_copy (const GstEvent *event);

Copy the event using the event specific copy function.

gst_event_steal ()

GstEvent *
gst_event_steal (GstEvent **old_event);

Atomically replace the GstEvent pointed to by old_event with NULL and return the original event.

gst_event_take ()

gboolean
gst_event_take (GstEvent **old_event,
                GstEvent *new_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.

gst_event_is_writable()

#define         gst_event_is_writable(ev)     gst_mini_object_is_writable (GST_MINI_OBJECT_CAST (ev))

Tests if you can safely write data into a event's structure or validly modify the seqnum and timestamp field.

gst_event_make_writable()

#define         gst_event_make_writable(ev)   GST_EVENT_CAST (gst_mini_object_make_writable (GST_MINI_OBJECT_CAST (ev)))

Makes a writable event from the given event. If the source event is already writable, this will simply return the same event. A copy will otherwise be made using gst_event_copy().

gst_event_writable_structure ()

GstStructure *
gst_event_writable_structure (GstEvent *event);

Get a writable version of the structure.

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.

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 have the same sequence number unless that correspondence was made explicitly.

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.

gst_event_get_running_time_offset ()

gint64
gst_event_get_running_time_offset (GstEvent *event);

Retrieve the accumulated running time offset of the event.

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

Since: 1.4

gst_event_set_running_time_offset ()

void
gst_event_set_running_time_offset (GstEvent *event,
                                   gint64 offset);

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

MT safe.

Since: 1.4

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_FLUSHING when used for data flow with gst_pad_push(), gst_pad_chain(), 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 (gboolean reset_time);

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.

gst_event_parse_flush_stop ()

void
gst_event_parse_flush_stop (GstEvent *event,
                            gboolean *reset_time);

Parse the FLUSH_STOP event and retrieve the reset_time member.

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_EOS 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.

The EOS event itself will not cause any state transitions of the pipeline.

gst_event_new_gap ()

GstEvent *
gst_event_new_gap (GstClockTime timestamp,
                   GstClockTime duration);

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.

gst_event_parse_gap ()

void
gst_event_parse_gap (GstEvent *event,
                     GstClockTime *timestamp,
                     GstClockTime *duration);

Extract timestamp and duration from a new GAP event.

gst_event_new_stream_start ()

GstEvent *
gst_event_new_stream_start (const gchar *stream_id);

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. gst_pad_create_stream_id() or gst_pad_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).

gst_event_parse_stream_start ()

void
gst_event_parse_stream_start (GstEvent *event,
                              const gchar **stream_id);

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.

gst_event_set_stream_flags ()

void
gst_event_set_stream_flags (GstEvent *event,
                            GstStreamFlags flags);

Since: 1.2

gst_event_parse_stream_flags ()

void
gst_event_parse_stream_flags (GstEvent *event,
                              GstStreamFlags *flags);

Since: 1.2

gst_event_set_group_id ()

void
gst_event_set_group_id (GstEvent *event,
                        guint group_id);

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

gst_event_parse_group_id ()

gboolean
gst_event_parse_group_id (GstEvent *event,
                          guint *group_id);

Since: 1.2

gst_event_new_segment ()

GstEvent *
gst_event_new_segment (const GstSegment *segment);

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)

gst_event_parse_segment ()

void
gst_event_parse_segment (GstEvent *event,
                         const GstSegment **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.

gst_event_copy_segment ()

void
gst_event_copy_segment (GstEvent *event,
                        GstSegment *segment);

Parses a segment event and copies the GstSegment into the location given by segment .

gst_event_new_tag ()

GstEvent *
gst_event_new_tag (GstTagList *taglist);

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.

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. 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.

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 preferred.

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 (GstQOSType type,
                   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 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.

gst_event_parse_qos ()

void
gst_event_parse_qos (GstEvent *event,
                     GstQOSType *type,
                     gdouble *proportion,
                     GstClockTimeDiff *diff,
                     GstClockTime *timestamp);

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

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

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 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.

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.

gst_event_parse_latency ()

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

Get the latency in the latency event.

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, 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.

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.

gst_event_new_sink_message ()

GstEvent *
gst_event_new_sink_message (const gchar *name,
                            GstMessage *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.

name is used to store multiple sticky events on one pad.

gst_event_parse_sink_message ()

void
gst_event_parse_sink_message (GstEvent *event,
                              GstMessage **msg);

Parse the sink-message event. Unref msg after usage.

gst_event_new_reconfigure ()

GstEvent *
gst_event_new_reconfigure (void);

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.

gst_event_new_caps ()

GstEvent *
gst_event_new_caps (GstCaps *caps);

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.

gst_event_parse_caps ()

void
gst_event_parse_caps (GstEvent *event,
                      GstCaps **caps);

Get the caps from event . The caps remains valid as long as event remains valid.

gst_event_new_toc ()

GstEvent *
gst_event_new_toc (GstToc *toc,
                   gboolean updated);

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.

gst_event_parse_toc ()

void
gst_event_parse_toc (GstEvent *event,
                     GstToc **toc,
                     gboolean *updated);

Parse a TOC event and store the results in the given toc and updated locations.

gst_event_new_toc_select ()

GstEvent *
gst_event_new_toc_select (const gchar *uid);

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 .

gst_event_parse_toc_select ()

void
gst_event_parse_toc_select (GstEvent *event,
                            gchar **uid);

Parse a TOC select event and store the results in the given uid location.

gst_event_new_segment_done ()

GstEvent *
gst_event_new_segment_done (GstFormat format,
                            gint64 position);

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.

gst_event_parse_segment_done ()

void
gst_event_parse_segment_done (GstEvent *event,
                              GstFormat *format,
                              gint64 *position);

Extracts the position and format from the segment done message.

gst_event_new_protection ()

GstEvent *
gst_event_new_protection (const gchar *system_id,
                          GstBuffer *data,
                          const gchar *origin);

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 gst_event_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.

Since: 1.6

gst_event_parse_protection ()

void
gst_event_parse_protection (GstEvent *event,
                            const gchar **system_id,
                            GstBuffer **data,
                            const gchar **origin);

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.

Since: 1.6

struct GstEvent

struct GstEvent {
  GstMiniObject mini_object;

  GstEventType  type;
  guint64       timestamp;
  guint32       seqnum;
};

A GstEvent.

enum 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.

enum 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.

enum GstStreamFlags

Since: 1.2

enum GstQOSType

The different types of QoS events that can be given to the gst_event_new_qos() method.

enum GstSeekType

The different types of seek events. When constructing a seek event with gst_event_new_seek() or when doing gst_segment_do_seek().

enum 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 emitted 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 seamless looping or simple linear editing.

When doing fast forward (rate > 1.0) or fast reverse (rate < -1.0) trickmode playback, the GST_SEEK_FLAG_TRICKMODE 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.

Beyond that, the GST_SEEK_FLAG_TRICKMODE_KEY_UNITS flag can be used to request that decoders skip all frames except key units, and GST_SEEK_FLAG_TRICKMODE_NO_AUDIO flags can be used to request that audio decoders do no decoding at all, and simple output silence.

The GST_SEEK_FLAG_SNAP_BEFORE flag can be used to snap to the previous relevant location, and the GST_SEEK_FLAG_SNAP_AFTER flag can be used to select the next relevant location. If GST_SEEK_FLAG_KEY_UNIT is specified, the relevant location is a keyframe. If both flags are specified, the nearest of these locations will be selected. If none are specified, the implementation is free to select whichever it wants.

The before and after here are in running time, so when playing backwards, the next location refers to the one that will played in next, and not the one that is located after in the actual source stream.

Also see part-seeking.txt in the GStreamer design documentation for more details on the meaning of these flags and the behaviour expected of elements that handle them.