Struct gstreamer_base::BaseParse

pub struct BaseParse { /* private fields */ }

This base class is for parser elements that process data and splits it into separate audio/video/whatever frames.

It provides for:

• provides one sink pad and one source pad
• handles state changes
• can operate in pull mode or push mode
• handles seeking in both modes
• handles events (SEGMENT/EOS/FLUSH)
• handles queries (POSITION/DURATION/SEEKING/FORMAT/CONVERT)
• handles flushing

The purpose of this base class is to provide the basic functionality of a parser and share a lot of rather complex code.

Description of the parsing mechanism:

Set-up phase

• BaseParse calls GstBaseParseClass::start to inform subclass that data processing is about to start now.

• BaseParse class calls GstBaseParseClass::set_sink_caps to inform the subclass about incoming sinkpad caps. Subclass could already set the srcpad caps accordingly, but this might be delayed until calling BaseParseExtManual::finish_frame() with a non-queued frame.

• At least at this point subclass needs to tell the BaseParse class how big data chunks it wants to receive (minimum frame size ). It can do this with BaseParseExt::set_min_frame_size().

• BaseParse class sets up appropriate data passing mode (pull/push) and starts to process the data.

Parsing phase

• BaseParse gathers at least min_frame_size bytes of data either by pulling it from upstream or collecting buffers in an internal Adapter.

• A buffer of (at least) min_frame_size bytes is passed to subclass with GstBaseParseClass::handle_frame. Subclass checks the contents and can optionally return gst::FlowReturn::Ok along with an amount of data to be skipped to find a valid frame (which will result in a subsequent DISCONT). If, otherwise, the buffer does not hold a complete frame, GstBaseParseClass::handle_frame can merely return and will be called again when additional data is available. In push mode this amounts to an additional input buffer (thus minimal additional latency), in pull mode this amounts to some arbitrary reasonable buffer size increase.

Of course, BaseParseExt::set_min_frame_size() could also be used if a very specific known amount of additional data is required. If, however, the buffer holds a complete valid frame, it can pass the size of this frame to BaseParseExtManual::finish_frame().

If acting as a converter, it can also merely indicate consumed input data while simultaneously providing custom output data. Note that baseclass performs some processing (such as tracking overall consumed data rate versus duration) for each finished frame, but other state is only updated upon each call to GstBaseParseClass::handle_frame (such as tracking upstream input timestamp).

Subclass is also responsible for setting the buffer metadata (e.g. buffer timestamp and duration, or keyframe if applicable). (although the latter can also be done by BaseParse if it is appropriately configured, see below). Frame is provided with timestamp derived from upstream (as much as generally possible), duration obtained from configuration (see below), and offset if meaningful (in pull mode).

Note that GstBaseParseClass::handle_frame might receive any small amount of input data when leftover data is being drained (e.g. at EOS).

• As part of finish frame processing, just prior to actually pushing the buffer in question, it is passed to GstBaseParseClass::pre_push_frame which gives subclass yet one last chance to examine buffer metadata, or to send some custom (tag) events, or to perform custom (segment) filtering.

• During the parsing process GstBaseParseClass will handle both srcpad and sinkpad events. They will be passed to subclass if GstBaseParseClass::sink_event or GstBaseParseClass::src_event implementations have been provided.

Shutdown phase

• BaseParse class calls GstBaseParseClass::stop to inform the subclass that data parsing will be stopped.

Subclass is responsible for providing pad template caps for source and sink pads. The pads need to be named “sink” and “src”. It also needs to set the fixed caps on srcpad, when the format is ensured (e.g. when base class calls subclass’ GstBaseParseClass::set_sink_caps function).

This base class uses gst::Format::Default as a meaning of frames. So, subclass conversion routine needs to know that conversion from gst::Format::Time to gst::Format::Default must return the frame number that can be found from the given byte position.

BaseParse uses subclasses conversion methods also for seeking (or otherwise uses its own default one, see also below).

Subclass start and stop functions will be called to inform the beginning and end of data processing.

Things that subclass need to take care of:

• Provide pad templates

• Fixate the source pad caps when appropriate

• Inform base class how big data chunks should be retrieved. This is done with BaseParseExt::set_min_frame_size() function.

• Examine data chunks passed to subclass with GstBaseParseClass::handle_frame and pass proper frame(s) to BaseParseExtManual::finish_frame(), and setting src pad caps and timestamps on frame.

• Provide conversion functions

• Update the duration information with BaseParseExtManual::set_duration()

• Optionally passthrough using BaseParseExt::set_passthrough()

• Configure various baseparse parameters using BaseParseExt::set_average_bitrate(), BaseParseExt::set_syncable() and BaseParseExtManual::set_frame_rate().

• In particular, if subclass is unable to determine a duration, but parsing (or specs) yields a frames per seconds rate, then this can be provided to BaseParse to enable it to cater for buffer time metadata (which will be taken from upstream as much as possible). Internally keeping track of frame durations and respective sizes that have been pushed provides BaseParse with an estimated bitrate. A default GstBaseParseClass::convert (used if not overridden) will then use these rates to perform obvious conversions. These rates are also used to update (estimated) duration at regular frame intervals.

This is an Abstract Base Class, you cannot instantiate it.

Properties

disable-passthrough

If set to true, baseparse will unconditionally force parsing of the incoming data. This can be required in the rare cases where the incoming side-data (caps, pts, dts, …) is not trusted by the user and wants to force validation and parsing of the incoming data. If set to false, decision of whether to parse the data or not is up to the implementation (standard behaviour).

Readable | Writeable

Object

name

Readable | Writeable | Construct

parent

The parent of the object. Please note, that when changing the ‘parent’ property, we don’t emit notify and deep-notify signals due to locking issues. In some cases one can use GstBin::element-added or GstBin::element-removed signals on the parent to achieve a similar effect.

Readable | Writeable

Implements

BaseParseExt, gst::prelude::ElementExt, gst::prelude::ObjectExt, [trait@glib::ObjectExt], BaseParseExtManual

GLib type: GObject with reference counted clone semantics.

Implementations

impl BaseParse

pub const NONE: Option<&'static BaseParse> = None

Trait Implementations

impl Clone for BaseParse

fn clone(&self) -> Self

Makes a clone of this shared reference.

This increments the strong reference count of the object. Dropping the object will decrement it again.

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

Performs copy-assignment from source.

impl Debug for BaseParse

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

Formats the value using the given formatter.

impl HasParamSpec for BaseParse

type ParamSpec = ParamSpecObject

type SetValue = BaseParse

Preferred value to be used as setter for the associated ParamSpec.

type BuilderFn = fn(_: &str) -> ParamSpecObjectBuilder<'_, BaseParse>

fn param_spec_builder() -> Self::BuilderFn

impl Hash for BaseParse

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

where H: Hasher,

Hashes the memory address of this object.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<T: BaseParseImpl> IsSubclassable<T> for BaseParse

fn class_init(klass: &mut Class<Self>)

Override the virtual methods of this class for the given subclass and do other class initialization.

fn instance_init(instance: &mut InitializingObject<T>)

Instance specific initialization.

impl Ord for BaseParse

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

Comparison for two GObjects.

Compares the memory addresses of the provided objects.

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

where Self: Sized,

Compares and returns the maximum of two values.

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

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl ParentClassIs for BaseParse

type Parent = Element

impl<OT: ObjectType> PartialEq<OT> for BaseParse

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

Equality for two GObjects.

Two GObjects are equal if their memory addresses are equal.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<OT: ObjectType> PartialOrd<OT> for BaseParse

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

Partial comparison for two GObjects.

Compares the memory addresses of the provided objects.

fn lt(&self, other: &Rhs) -> bool

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

fn le(&self, other: &Rhs) -> bool

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

fn gt(&self, other: &Rhs) -> bool

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

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 StaticType for BaseParse

fn static_type() -> Type

Returns the type identifier of Self.

impl Eq for BaseParse

impl IsA<Element> for BaseParse

impl IsA<Object> for BaseParse

impl Send for BaseParse

impl Sync for BaseParse