Struct gstreamer_base::BaseSrc

pub struct BaseSrc(_, _);

This is a generic base class for source elements. The following types of sources are supported:

• random access sources like files
• seekable sources
• live sources

The source can be configured to operate in any gst::Format with the BaseSrcExt::set_format method. The currently set format determines the format of the internal gst::Segment and any gst::EventType::Segment events. The default format for BaseSrc is gst::Format::Bytes.

BaseSrc always supports push mode scheduling. If the following conditions are met, it also supports pull mode scheduling:

• The format is set to gst::Format::Bytes (default).
• BaseSrcClass.is_seekable() returns true.

If all the conditions are met for operating in pull mode, BaseSrc is automatically seekable in push mode as well. The following conditions must be met to make the element seekable in push mode when the format is not gst::Format::Bytes:

• BaseSrcClass.is_seekable() returns true.
• BaseSrcClass.query() can convert all supported seek formats to the internal format as set with BaseSrcExt::set_format.
• BaseSrcClass.do_seek() is implemented, performs the seek and returns true.

When the element does not meet the requirements to operate in pull mode, the offset and length in the BaseSrcClass.create() method should be ignored. It is recommended to subclass PushSrc instead, in this situation. If the element can operate in pull mode but only with specific offsets and lengths, it is allowed to generate an error when the wrong values are passed to the BaseSrcClass.create() function.

BaseSrc has support for live sources. Live sources are sources that when paused discard data, such as audio or video capture devices. A typical live source also produces data at a fixed rate and thus provides a clock to publish this rate. Use BaseSrcExt::set_live to activate the live source mode.

A live source does not produce data in the PAUSED state. This means that the BaseSrcClass.create() method will not be called in PAUSED but only in PLAYING. To signal the pipeline that the element will not produce data, the return value from the READY to PAUSED state will be gst::StateChangeReturn::NoPreroll.

A typical live source will timestamp the buffers it creates with the current running time of the pipeline. This is one reason why a live source can only produce data in the PLAYING state, when the clock is actually distributed and running.

Live sources that synchronize and block on the clock (an audio source, for example) can use BaseSrcExt::wait_playing when the BaseSrcClass.create() function was interrupted by a state change to PAUSED.

The BaseSrcClass.get_times() method can be used to implement pseudo-live sources. It only makes sense to implement the BaseSrcClass.get_times() function if the source is a live source. The BaseSrcClass.get_times() function should return timestamps starting from 0, as if it were a non-live source. The base class will make sure that the timestamps are transformed into the current running_time. The base source will then wait for the calculated running_time before pushing out the buffer.

For live sources, the base class will by default report a latency of 0. For pseudo live sources, the base class will by default measure the difference between the first buffer timestamp and the start time of get_times and will report this value as the latency. Subclasses should override the query function when this behaviour is not acceptable.

There is only support in BaseSrc for exactly one source pad, which should be named "src". A source implementation (subclass of BaseSrc) 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);
  // srctemplate should be a #GstStaticPadTemplate with direction
  // %GST_PAD_SRC and name "src"
  gst_element_class_add_static_pad_template (gstelement_class, &srctemplate);

  gst_element_class_set_static_metadata (gstelement_class,
     "Source name",
     "Source",
     "My Source element",
     "The author <my.sink@my.email>");
}

Controlled shutdown of live sources in applications

Applications that record from a live source may want to stop recording in a controlled way, so that the recording is stopped, but the data already in the pipeline is processed to the end (remember that many live sources would go on recording forever otherwise). For that to happen the application needs to make the source stop recording and send an EOS event down the pipeline. The application would then wait for an EOS message posted on the pipeline's bus to know when all data has been processed and the pipeline can safely be stopped.

An application may send an EOS event to a source element to make it perform the EOS logic (send EOS event downstream or post a gst::MessageType::SegmentDone on the bus). This can typically be done with the gst::ElementExt::send_event function on the element or its parent bin.

After the EOS has been sent to the element, the application should wait for an EOS message to be posted on the pipeline's bus. Once this EOS message is received, it may safely shut down the entire pipeline.

Implements

BaseSrcExt, gst::ElementExt, gst::ObjectExt, glib::object::ObjectExt

Trait Implementations

impl Clone for BaseSrc

fn clone(&self) -> BaseSrc

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Hash for BaseSrc

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where     H: Hasher,

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

impl Ord for BaseSrc

fn cmp(&self, other: &BaseSrc) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

impl StaticType for BaseSrc

fn static_type() -> Type

Returns the type identifier of Self.

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

fn eq(&self, other: &T) -> bool

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

#[must_use] fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl Eq for BaseSrc

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

fn partial_cmp(&self, other: &T) -> Option<Ordering>

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

#[must_use] fn lt(&self, other: &Rhs) -> bool

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

#[must_use] fn le(&self, other: &Rhs) -> bool

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

#[must_use] fn gt(&self, other: &Rhs) -> bool

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

#[must_use] fn ge(&self, other: &Rhs) -> bool

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

impl Debug for BaseSrc

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl IsA<Element> for BaseSrc

impl IsA<Object> for BaseSrc

impl IsA<Object> for BaseSrc

impl Send for BaseSrc

impl Sync for BaseSrc

impl IsA<BaseSrc> for PushSrc