| Top | |
|
|
|
| gboolean | async | Read / Write |
| guint | blocksize | Read / Write |
| gboolean | enable-last-sample | Read / Write |
| GstSample * | last-sample | Read |
| guint64 | max-bitrate | Read / Write |
| gint64 | max-lateness | Read / Write |
| gboolean | qos | Read / Write |
| guint64 | render-delay | Read / Write |
| gboolean | sync | Read / Write |
| guint64 | throttle-time | Read / Write |
| gint64 | ts-offset | Read / Write |
GstBaseSink is the base class for sink elements in GStreamer, such as xvimagesink or filesink. It is a layer on top of GstElement that provides a simplified interface to plugin writers. GstBaseSink handles many details for you, for example: preroll, clock synchronization, state changes, activation in push or pull mode, and queries.
In most cases, when writing sink elements, there is no need to implement class methods from GstElement or to set functions on pads, because the GstBaseSink infrastructure should be sufficient.
GstBaseSink provides support for exactly one sink pad, which should be named "sink". A sink implementation (subclass of GstBaseSink) should install a pad template in its class_init function, like so:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
static void my_element_class_init (GstMyElementClass *klass) { GstElementClass *gstelement_class = GST_ELEMENT_CLASS (klass); // sinktemplate should be a #GstStaticPadTemplate with direction // %GST_PAD_SINK and name "sink" gst_element_class_add_pad_template (gstelement_class, gst_static_pad_template_get (&sinktemplate)); gst_element_class_set_static_metadata (gstelement_class, "Sink name", "Sink", "My Sink element", "The author <my.sink@my.email>"); } |
GstBaseSink will handle the prerolling correctly. This means that it will
return GST_STATE_CHANGE_ASYNC from a state change to PAUSED until the first
buffer arrives in this element. The base class will call the
GstBaseSinkClass.preroll() vmethod with this preroll buffer and will then
commit the state change to the next asynchronously pending state.
When the element is set to PLAYING, GstBaseSink will synchronise on the
clock using the times returned from GstBaseSinkClass.get_times(). If this
function returns GST_CLOCK_TIME_NONE for the start time, no synchronisation
will be done. Synchronisation can be disabled entirely by setting the object
“sync” property to FALSE.
After synchronisation the virtual method GstBaseSinkClass.render() will be
called. Subclasses should minimally implement this method.
Subclasses that synchronise on the clock in the GstBaseSinkClass.render()
method are supported as well. These classes typically receive a buffer in
the render method and can then potentially block on the clock while
rendering. A typical example is an audiosink.
These subclasses can use gst_base_sink_wait_preroll() to perform the
blocking wait.
Upon receiving the EOS event in the PLAYING state, GstBaseSink will wait
for the clock to reach the time indicated by the stop time of the last
GstBaseSinkClass.get_times() call before posting an EOS message. When the
element receives EOS in PAUSED, preroll completes, the event is queued and an
EOS message is posted when going to PLAYING.
GstBaseSink will internally use the GST_EVENT_SEGMENT events to schedule
synchronisation and clipping of buffers. Buffers that fall completely outside
of the current segment are dropped. Buffers that fall partially in the
segment are rendered (and prerolled). Subclasses should do any subbuffer
clipping themselves when needed.
GstBaseSink will by default report the current playback position in
GST_FORMAT_TIME based on the current clock time and segment information.
If no clock has been set on the element, the query will be forwarded
upstream.
The GstBaseSinkClass.set_caps() function will be called when the subclass
should configure itself to process a specific media type.
The GstBaseSinkClass.start() and GstBaseSinkClass.stop() virtual methods
will be called when resources should be allocated. Any
GstBaseSinkClass.preroll(), GstBaseSinkClass.render() and
GstBaseSinkClass.set_caps() function will be called between the
GstBaseSinkClass.start() and GstBaseSinkClass.stop() calls.
The GstBaseSinkClass.event() virtual method will be called when an event is
received by GstBaseSink. Normally this method should only be overridden by
very specific elements (such as file sinks) which need to handle the
newsegment event specially.
The GstBaseSinkClass.unlock() method is called when the elements should
unblock any blocking operations they perform in the
GstBaseSinkClass.render() method. This is mostly useful when the
GstBaseSinkClass.render() method performs a blocking write on a file
descriptor, for example.
The “max-lateness” property affects how the sink deals with
buffers that arrive too late in the sink. A buffer arrives too late in the
sink when the presentation time (as a combination of the last segment, buffer
timestamp and element base_time) plus the duration is before the current
time of the clock.
If the frame is later than max-lateness, the sink will drop the buffer
without calling the render method.
This feature is disabled if sync is disabled, the
GstBaseSinkClass.get_times() method does not return a valid start time or
max-lateness is set to -1 (the default).
Subclasses can use gst_base_sink_set_max_lateness() to configure the
max-lateness value.
The “qos” property will enable the quality-of-service features of the basesink which gather statistics about the real-time performance of the clock synchronisation. For each buffer received in the sink, statistics are gathered and a QOS event is sent upstream with these numbers. This information can then be used by upstream elements to reduce their processing rate, for example.
The “async” property can be used to instruct the sink to never perform an ASYNC state change. This feature is mostly usable when dealing with non-synchronized streams or sparse streams.
gboolean gst_base_sink_query_latency (GstBaseSink *sink,gboolean *live,gboolean *upstream_live,GstClockTime *min_latency,GstClockTime *max_latency);
Query the sink for the latency parameters. The latency will be queried from
the upstream elements. live
will be TRUE if sink
is configured to
synchronize against the clock. upstream_live
will be TRUE if an upstream
element is live.
If both live
and upstream_live
are TRUE, the sink will want to compensate
for the latency introduced by the upstream elements by setting the
min_latency
to a strictly positive value.
This function is mostly used by subclasses.
GstClockTime
gst_base_sink_get_latency (GstBaseSink *sink);
Get the currently configured latency.
GstFlowReturn gst_base_sink_do_preroll (GstBaseSink *sink,GstMiniObject *obj);
If the sink
spawns its own thread for pulling buffers from upstream it
should call this method after it has pulled a buffer. If the element needed
to preroll, this function will perform the preroll and will then block
until the element state is changed.
This function should be called with the PREROLL_LOCK held.
GST_FLOW_OK if the preroll completed and processing can
continue. Any other return value should be returned from the render vmethod.
GstFlowReturn gst_base_sink_wait (GstBaseSink *sink,GstClockTime time,GstClockTimeDiff *jitter);
This function will wait for preroll to complete and will then block until time
is reached. It is usually called by subclasses that use their own internal
synchronisation but want to let some synchronization (like EOS) be handled
by the base class.
This function should only be called with the PREROLL_LOCK held (like when receiving an EOS event in the ::event vmethod or when handling buffers in ::render).
The time
argument should be the running_time of when the timeout should happen
and will be adjusted with any latency and offset configured in the sink.
sink |
the sink |
|
time |
the running_time to be reached |
|
jitter |
the jitter to be filled with time diff, or |
[out][allow-none] |
GstFlowReturn
gst_base_sink_wait_preroll (GstBaseSink *sink);
If the GstBaseSinkClass.render() method performs its own synchronisation
against the clock it must unblock when going from PLAYING to the PAUSED state
and call this method before continuing to render the remaining data.
This function will block until a state change to PLAYING happens (in which
case this function returns GST_FLOW_OK) or the processing must be stopped due
to a state change to READY or a FLUSH event (in which case this function
returns GST_FLOW_FLUSHING).
This function should only be called with the PREROLL_LOCK held, like in the render function.
GST_FLOW_OK if the preroll completed and processing can
continue. Any other return value should be returned from the render vmethod.
GstClockReturn gst_base_sink_wait_clock (GstBaseSink *sink,GstClockTime time,GstClockTimeDiff *jitter);
This function will block until time
is reached. It is usually called by
subclasses that use their own internal synchronisation.
If time
is not valid, no synchronisation is done and GST_CLOCK_BADTIME is
returned. Likewise, if synchronisation is disabled in the element or there
is no clock, no synchronisation is done and GST_CLOCK_BADTIME is returned.
This function should only be called with the PREROLL_LOCK held, like when
receiving an EOS event in the GstBaseSinkClass.event() vmethod or when
receiving a buffer in
the GstBaseSinkClass.render() vmethod.
The time
argument should be the running_time of when this method should
return and is not adjusted with any latency or offset configured in the
sink.
sink |
the sink |
|
time |
the running_time to be reached |
|
jitter |
the jitter to be filled with time diff, or |
[out][allow-none] |
void gst_base_sink_set_sync (GstBaseSink *sink,gboolean sync);
Configures sink
to synchronize on the clock or not. When
sync
is FALSE, incoming samples will be played as fast as
possible. If sync
is TRUE, the timestamps of the incoming
buffers will be used to schedule the exact render time of its
contents.
gboolean
gst_base_sink_get_sync (GstBaseSink *sink);
Checks if sink
is currently configured to synchronize against the
clock.
void gst_base_sink_set_max_lateness (GstBaseSink *sink,gint64 max_lateness);
Sets the new max lateness value to max_lateness
. This value is
used to decide if a buffer should be dropped or not based on the
buffer timestamp and the current clock time. A value of -1 means
an unlimited time.
gint64
gst_base_sink_get_max_lateness (GstBaseSink *sink);
Gets the max lateness value. See gst_base_sink_set_max_lateness for more details.
void gst_base_sink_set_qos_enabled (GstBaseSink *sink,gboolean enabled);
Configures sink
to send Quality-of-Service events upstream.
gboolean
gst_base_sink_is_qos_enabled (GstBaseSink *sink);
Checks if sink
is currently configured to send Quality-of-Service events
upstream.
void gst_base_sink_set_async_enabled (GstBaseSink *sink,gboolean enabled);
Configures sink
to perform all state changes asynchronously. When async is
disabled, the sink will immediately go to PAUSED instead of waiting for a
preroll buffer. This feature is useful if the sink does not synchronize
against the clock or when it is dealing with sparse streams.
gboolean
gst_base_sink_is_async_enabled (GstBaseSink *sink);
Checks if sink
is currently configured to perform asynchronous state
changes to PAUSED.
void gst_base_sink_set_ts_offset (GstBaseSink *sink,GstClockTimeDiff offset);
Adjust the synchronisation of sink
with offset
. A negative value will
render buffers earlier than their timestamp. A positive value will delay
rendering. This function can be used to fix playback of badly timestamped
buffers.
GstClockTimeDiff
gst_base_sink_get_ts_offset (GstBaseSink *sink);
Get the synchronisation offset of sink
.
void gst_base_sink_set_render_delay (GstBaseSink *sink,GstClockTime delay);
Set the render delay in sink
to delay
. The render delay is the time
between actual rendering of a buffer and its synchronisation time. Some
devices might delay media rendering which can be compensated for with this
function.
After calling this function, this sink will report additional latency and other sinks will adjust their latency to delay the rendering of their media.
This function is usually called by subclasses.
GstClockTime
gst_base_sink_get_render_delay (GstBaseSink *sink);
Get the render delay of sink
. see gst_base_sink_set_render_delay() for more
information about the render delay.
GstSample *
gst_base_sink_get_last_sample (GstBaseSink *sink);
Get the last sample that arrived in the sink and was used for preroll or for rendering. This property can be used to generate thumbnails.
The GstCaps on the sample can be used to determine the type of the buffer.
Free-function: gst_sample_unref
a GstSample. gst_sample_unref() after
usage. This function returns NULL when no buffer has arrived in the
sink yet or when the sink is not in PAUSED or PLAYING.
[transfer full][nullable]
void gst_base_sink_set_blocksize (GstBaseSink *sink,guint blocksize);
Set the number of bytes that the sink will pull when it is operating in pull mode.
guint
gst_base_sink_get_blocksize (GstBaseSink *sink);
Get the number of bytes that the sink will pull when it is operating in pull mode.
guint64
gst_base_sink_get_throttle_time (GstBaseSink *sink);
Get the time that will be inserted between frames to control the maximum buffers per second.
void gst_base_sink_set_throttle_time (GstBaseSink *sink,guint64 throttle);
Set the time that will be inserted between rendered buffers. This can be used to control the maximum buffers per second that the sink will render.
void gst_base_sink_set_max_bitrate (GstBaseSink *sink,guint64 max_bitrate);
Set the maximum amount of bits per second that the sink will render.
Since: 1.2
guint64
gst_base_sink_get_max_bitrate (GstBaseSink *sink);
Get the maximum amount of bits per second that the sink will render.
Since: 1.2
void gst_base_sink_set_last_sample_enabled (GstBaseSink *sink,gboolean enabled);
Configures sink
to store the last received sample in the last-sample
property.
gboolean
gst_base_sink_is_last_sample_enabled (GstBaseSink *sink);
Checks if sink
is currently configured to store the last received sample in
the last-sample property.
#define GST_BASE_SINK_PAD(obj) (GST_BASE_SINK_CAST (obj)->sinkpad)
Gives the pointer to the GstPad object of the element.
#define GST_BASE_SINK_GET_PREROLL_COND(pad) (&GST_BASE_SINK_CAST(pad)->preroll_cond)
#define GST_BASE_SINK_GET_PREROLL_LOCK(pad) (&GST_BASE_SINK_CAST(pad)->preroll_lock)
#define GST_BASE_SINK_PREROLL_BROADCAST(pad) g_cond_broadcast (GST_BASE_SINK_GET_PREROLL_COND (pad));
#define GST_BASE_SINK_PREROLL_LOCK(pad) (g_mutex_lock(GST_BASE_SINK_GET_PREROLL_LOCK(pad)))
#define GST_BASE_SINK_PREROLL_SIGNAL(pad) g_cond_signal (GST_BASE_SINK_GET_PREROLL_COND (pad));
#define GST_BASE_SINK_PREROLL_TRYLOCK(pad) (g_mutex_trylock(GST_BASE_SINK_GET_PREROLL_LOCK(pad)))
#define GST_BASE_SINK_PREROLL_UNLOCK(pad) (g_mutex_unlock(GST_BASE_SINK_GET_PREROLL_LOCK(pad)))
struct GstBaseSinkClass {
GstElementClass parent_class;
/* get caps from subclass */
GstCaps* (*get_caps) (GstBaseSink *sink, GstCaps *filter);
/* notify subclass of new caps */
gboolean (*set_caps) (GstBaseSink *sink, GstCaps *caps);
/* fixate sink caps during pull-mode negotiation */
GstCaps * (*fixate) (GstBaseSink *sink, GstCaps *caps);
/* start or stop a pulling thread */
gboolean (*activate_pull)(GstBaseSink *sink, gboolean active);
/* get the start and end times for syncing on this buffer */
void (*get_times) (GstBaseSink *sink, GstBuffer *buffer,
GstClockTime *start, GstClockTime *end);
/* propose allocation parameters for upstream */
gboolean (*propose_allocation) (GstBaseSink *sink, GstQuery *query);
/* start and stop processing, ideal for opening/closing the resource */
gboolean (*start) (GstBaseSink *sink);
gboolean (*stop) (GstBaseSink *sink);
/* unlock any pending access to the resource. subclasses should unlock
* any function ASAP. */
gboolean (*unlock) (GstBaseSink *sink);
/* Clear a previously indicated unlock request not that unlocking is
* complete. Sub-classes should clear any command queue or indicator they
* set during unlock */
gboolean (*unlock_stop) (GstBaseSink *sink);
/* notify subclass of query */
gboolean (*query) (GstBaseSink *sink, GstQuery *query);
/* notify subclass of event */
gboolean (*event) (GstBaseSink *sink, GstEvent *event);
/* wait for eos or gap, subclasses should chain up to parent first */
GstFlowReturn (*wait_event) (GstBaseSink *sink, GstEvent *event);
/* notify subclass of buffer or list before doing sync */
GstFlowReturn (*prepare) (GstBaseSink *sink, GstBuffer *buffer);
GstFlowReturn (*prepare_list) (GstBaseSink *sink, GstBufferList *buffer_list);
/* notify subclass of preroll buffer or real buffer */
GstFlowReturn (*preroll) (GstBaseSink *sink, GstBuffer *buffer);
GstFlowReturn (*render) (GstBaseSink *sink, GstBuffer *buffer);
/* Render a BufferList */
GstFlowReturn (*render_list) (GstBaseSink *sink, GstBufferList *buffer_list);
};
Subclasses can override any of the available virtual methods or not, as
needed. At the minimum, the render
method should be overridden to
output/present buffers.
GstElementClass |
Element parent class |
|
Called to get sink pad caps from the subclass |
||
Notify subclass of changed caps |
||
Only useful in pull mode. Implement if you have ideas about what should be the default values for the caps you support. |
||
Subclasses should override this when they can provide an alternate method of spawning a thread to drive the pipeline in pull mode. Should start or stop the pulling thread, depending on the value of the "active" argument. Called after actually activating the sink pad in pull mode. The default implementation starts a task on the sink pad. |
||
Called to get the start and end times for synchronising the passed buffer to the clock |
||
configure the allocation query |
||
Start processing. Ideal for opening resources in the subclass |
||
Stop processing. Subclasses should use this to close resources. |
||
Unlock any pending access to the resource. Subclasses should unblock any blocked function ASAP |
||
Clear the previous unlock request. Subclasses should clear
any state they set during |
||
perform a GstQuery on the element. |
||
Override this to handle events arriving on the sink pad |
||
Override this to implement custom logic to wait for the event time (for events like EOS and GAP). Subclasses should always first chain up to the default implementation. |
||
Called to prepare the buffer for |
||
Called to prepare the buffer list for |
||
Called to present the preroll buffer if desired. |
||
Called when a buffer should be presented or output, at the correct moment if the GstBaseSink has been set to sync to the clock. |
||
Same as |
“async” property“async” gboolean
If set to TRUE, the basesink will perform asynchronous state changes.
When set to FALSE, the sink will not signal the parent when it prerolls.
Use this option when dealing with sparse streams or when synchronisation is
not required.
Flags: Read / Write
Default value: TRUE
“blocksize” property“blocksize” guint
The amount of bytes to pull when operating in pull mode.
Flags: Read / Write
Default value: 4096
“enable-last-sample” property“enable-last-sample” gboolean
Enable the last-sample property. If FALSE, basesink doesn't keep a
reference to the last buffer arrived and the last-sample property is always
set to NULL. This can be useful if you need buffers to be released as soon
as possible, eg. if you're using a buffer pool.
Flags: Read / Write
Default value: TRUE
“last-sample” property“last-sample” GstSample *
The last buffer that arrived in the sink and was used for preroll or for
rendering. This property can be used to generate thumbnails. This property
can be NULL when the sink has not yet received a buffer.
Flags: Read
“max-bitrate” property “max-bitrate” guint64
Control the maximum amount of bits that will be rendered per second. Setting this property to a value bigger than 0 will make the sink delay rendering of the buffers when it would exceed to max-bitrate.
Flags: Read / Write
Default value: 0
Since: 1.2
“max-lateness” property “max-lateness” gint64
Maximum number of nanoseconds that a buffer can be late before it is dropped (-1 unlimited).
Flags: Read / Write
Allowed values: >= -1
Default value: -1
“qos” property“qos” gboolean
Generate Quality-of-Service events upstream.
Flags: Read / Write
Default value: FALSE
“render-delay” property “render-delay” guint64
The additional delay between synchronisation and actual rendering of the media. This property will add additional latency to the device in order to make other sinks compensate for the delay.
Flags: Read / Write
Default value: 0
“throttle-time” property “throttle-time” guint64
The time to insert between buffers. This property can be used to control the maximum amount of buffers per second to render. Setting this property to a value bigger than 0 will make the sink create THROTTLE QoS events.
Flags: Read / Write
Default value: 0