Pipeline

class Pipeline(**properties: Any)

Superclasses: Bin, Element, Object, InitiallyUnowned, Object

Implemented Interfaces: ChildProxy

A Pipeline is a special Bin used as the toplevel container for the filter graph. The Pipeline will manage the selection and distribution of a global Clock as well as provide a Bus to the application.

new() is used to create a pipeline. when you are done with the pipeline, use unref() to free its resources including all added Element objects (if not otherwise referenced).

Elements are added and removed from the pipeline using the Bin methods like add() and remove() (see Bin).

Before changing the state of the Pipeline (see Element) a Bus should be retrieved with get_bus(). This Bus should then be used to receive Message from the elements in the pipeline. Listening to the Bus is necessary for retrieving error messages from the Pipeline and otherwise the Pipeline might stop without any indication, why. Furthermore, the Pipeline posts messages even if nobody listens on the Bus, which will pile up and use up memory.

By default, a Pipeline will automatically flush the pending Bus messages when going to the NULL state to ensure that no circular references exist when no messages are read from the Bus. This behaviour can be changed with set_auto_flush_bus().

When the Pipeline performs the PAUSED to PLAYING state change it will select a clock for the elements. The clock selection algorithm will by default select a clock provided by an element that is most upstream (closest to the source). For live pipelines (ones that return GST_STATE_CHANGE_NO_PREROLL from the set_state() call) this will select the clock provided by the live source. For normal pipelines this will select a clock provided by the sinks (most likely the audio sink). If no element provides a clock, a default GstSystemClock is used.

The clock selection can be controlled with the use_clock() method, which will enforce a given clock on the pipeline. With auto_clock() the default clock selection algorithm can be restored.

A Pipeline maintains a running time for the elements. The running time is defined as the difference between the current clock time and the base time. When the pipeline goes to READY or a flushing seek is performed on it, the running time is reset to 0. When the pipeline is set from PLAYING to PAUSED, the current clock time is sampled and used to configure the base time for the elements when the pipeline is set to PLAYING again. The effect is that the running time (as the difference between the clock time and the base time) will count how much time was spent in the PLAYING state. This default behaviour can be changed with the set_start_time() method.

Constructors

class Pipeline

classmethod new(name: str | None = None) → Element

Create a new pipeline with the given name.

Parameters:: name – name of new pipeline

Methods

class Pipeline

auto_clock() → None

Let pipeline select a clock automatically. This is the default behaviour.

Use this function if you previous forced a fixed clock with use_clock() and want to restore the default pipeline clock selection algorithm.

MT safe.

get_auto_flush_bus() → bool: Check if pipeline will automatically flush messages when going to the NULL state.

get_bus() → Bus: Gets the Bus of pipeline. The bus allows applications to receive Message packets.

get_delay() → int: Get the configured delay (see set_delay()).

get_latency() → int: Gets the latency that should be configured on the pipeline. See set_latency().

Added in version 1.6.

get_pipeline_clock() → Clock

Gets the current clock used by pipeline.

Unlike get_clock(), this function will always return a clock, even if the pipeline is not in the PLAYING state.

Added in version 1.6.

set_auto_flush_bus(auto_flush: bool) → None

Usually, when a pipeline goes from READY to NULL state, it automatically flushes all pending messages on the bus, which is done for refcounting purposes, to break circular references.

This means that applications that update state using (async) bus messages (e.g. do certain things when a pipeline goes from PAUSED to READY) might not get to see messages when the pipeline is shut down, because they might be flushed before they can be dispatched in the main thread. This behaviour can be disabled using this function.

It is important that all messages on the bus are handled when the automatic flushing is disabled else memory leaks will be introduced.

MT safe.

Parameters:: auto_flush – whether or not to automatically flush the bus when the pipeline goes from READY to NULL state

set_delay(delay: int) → None

Set the expected delay needed for all elements to perform the PAUSED to PLAYING state change. delay will be added to the base time of the elements so that they wait an additional delay amount of time before starting to process buffers and cannot be GST_CLOCK_TIME_NONE.

This option is used for tuning purposes and should normally not be used.

MT safe.

Parameters:: delay – the delay

set_latency(latency: int) → None

Sets the latency that should be configured on the pipeline. Setting GST_CLOCK_TIME_NONE will restore the default behaviour of using the minimum latency from the LATENCY query. Setting this is usually not required and the pipeline will figure out an appropriate latency automatically.

Setting a too low latency, especially lower than the minimum latency from the LATENCY query, will most likely cause the pipeline to fail.

Added in version 1.6.

Parameters:: latency – latency to configure

use_clock(clock: Clock | None = None) → None

Force pipeline to use the given clock. The pipeline will always use the given clock even if new clock providers are added to this pipeline.

If clock is None all clocking will be disabled which will make the pipeline run as fast as possible.

MT safe.

Parameters:: clock – the clock to use

Properties

class Pipeline

props.auto_flush_bus: bool: Whether or not to automatically flush all messages on the pipeline’s bus when going from READY to NULL state. Please see set_auto_flush_bus() for more information on this option.

props.delay: int: The expected delay needed for elements to spin up to the PLAYING state expressed in nanoseconds. see set_delay() for more information on this option.

props.latency: int: Latency to configure on the pipeline. See set_latency().

Added in version 1.6.

Fields

class Pipeline

bin

delay: Extra delay added to base_time to compensate for computing delays when setting elements to PLAYING.

fixed_clock: The fixed clock of the pipeline, used when GST_PIPELINE_FLAG_FIXED_CLOCK is set.

priv

stream_time: The stream time of the pipeline. A better name for this property would be the running_time, the total time spent in the PLAYING state without being flushed. (deprecated, use the start_time on GstElement).