Struct gstreamer_base::BaseSink[]

pub struct BaseSink(_, _);

BaseSink is the base class for sink elements in GStreamer, such as xvimagesink or filesink. It is a layer on top of gst::Element that provides a simplified interface to plugin writers. BaseSink 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 gst::Element or to set functions on pads, because the BaseSink infrastructure should be sufficient.

BaseSink provides support for exactly one sink pad, which should be named "sink". A sink implementation (subclass of BaseSink) should install a pad template in its class_init function, like so:

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_static_pad_template (gstelement_class, &sinktemplate);

  gst_element_class_set_static_metadata (gstelement_class,
      "Sink name",
      "My Sink element",
      "The author <>");

BaseSink will handle the prerolling correctly. This means that it will return gst::StateChangeReturn::Async from a state change to PAUSED until the first buffer arrives in this element. The base class will call the BaseSinkClass.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, BaseSink will synchronise on the clock using the times returned from BaseSinkClass.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 BaseSink:sync property to false.

After synchronisation the virtual method BaseSinkClass.render() will be called. Subclasses should minimally implement this method.

Subclasses that synchronise on the clock in the BaseSinkClass.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 BaseSinkExt::wait_preroll to perform the blocking wait.

Upon receiving the EOS event in the PLAYING state, BaseSink will wait for the clock to reach the time indicated by the stop time of the last BaseSinkClass.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.

BaseSink will internally use the gst::EventType::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.

BaseSink 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 BaseSinkClass.set_caps() function will be called when the subclass should configure itself to process a specific media type.

The BaseSinkClass.start() and BaseSinkClass.stop() virtual methods will be called when resources should be allocated. Any BaseSinkClass.preroll(), BaseSinkClass.render() and BaseSinkClass.set_caps() function will be called between the BaseSinkClass.start() and BaseSinkClass.stop() calls.

The BaseSinkClass.event() virtual method will be called when an event is received by BaseSink. Normally this method should only be overridden by very specific elements (such as file sinks) which need to handle the newsegment event specially.

The BaseSinkClass.unlock() method is called when the elements should unblock any blocking operations they perform in the BaseSinkClass.render() method. This is mostly useful when the BaseSinkClass.render() method performs a blocking write on a file descriptor, for example.

The BaseSink: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 BaseSinkClass.get_times() method does not return a valid start time or max-lateness is set to -1 (the default). Subclasses can use BaseSinkExt::set_max_lateness to configure the max-lateness value.

The BaseSink: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 BaseSink: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.


BaseSinkExt, gst::ElementExt, gst::ObjectExt, glib::object::ObjectExt

Trait Implementations

impl Clone for BaseSink

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl Hash for BaseSink

Feeds this value into the given [Hasher]. Read more

Feeds a slice of this type into the given [Hasher]. Read more

impl Ord for BaseSink

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

impl StaticType for BaseSink

Returns the type identifier of Self.

impl<T: IsA<Object>> PartialEq<T> for BaseSink

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

impl Eq for BaseSink

impl<T: IsA<Object>> PartialOrd<T> for BaseSink

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

impl Debug for BaseSink

Formats the value using the given formatter. Read more

impl IsA<Element> for BaseSink

impl IsA<Object> for BaseSink

impl IsA<Object> for BaseSink

impl Send for BaseSink

impl Sync for BaseSink