GstPipeline

GstPipeline — Top-level bin with clocking and bus management functionality.

Functions

Properties

gboolean auto-flush-bus Read / Write
guint64 delay Read / Write

Types and Values

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstElement
                ╰── GstBin
                    ╰── GstPipeline

Implemented Interfaces

GstPipeline implements GstChildProxy.

Includes

#include <gst/gst.h>

Description

A GstPipeline is a special GstBin used as the toplevel container for the filter graph. The GstPipeline will manage the selection and distribution of a global GstClock as well as provide a GstBus to the application.

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

Elements are added and removed from the pipeline using the GstBin methods like gst_bin_add() and gst_bin_remove() (see GstBin).

Before changing the state of the GstPipeline (see GstElement) a GstBus can be retrieved with gst_pipeline_get_bus(). This bus can then be used to receive GstMessage from the elements in the pipeline.

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

When the GstPipeline 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 gst_element_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 gst_pipeline_use_clock() method, which will enforce a given clock on the pipeline. With gst_pipeline_auto_clock() the default clock selection algorithm can be restored.

A GstPipeline 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 gst_element_set_start_time() method.

Last reviewed on 2012-03-29 (0.11.3)

Functions

gst_pipeline_new ()

GstElement *
gst_pipeline_new (const gchar *name);

Create a new pipeline with the given name.

Parameters

name

name of new pipeline.

[allow-none]

Returns

newly created GstPipeline

MT safe.

[transfer floating]


gst_pipeline_get_bus ()

GstBus *
gst_pipeline_get_bus (GstPipeline *pipeline);

Gets the GstBus of pipeline . The bus allows applications to receive GstMessage packets.

Parameters

pipeline

a GstPipeline

 

Returns

a GstBus, unref after usage.

MT safe.

[transfer full]


gst_pipeline_set_clock ()

gboolean
gst_pipeline_set_clock (GstPipeline *pipeline,
                        GstClock *clock);

Set the clock for pipeline . The clock will be distributed to all the elements managed by the pipeline.

Parameters

pipeline

a GstPipeline

 

clock

the clock to set.

[transfer none]

Returns

TRUE if the clock could be set on the pipeline. FALSE if some element did not accept the clock.

MT safe.


gst_pipeline_get_clock ()

GstClock *
gst_pipeline_get_clock (GstPipeline *pipeline);

Gets the current clock used by pipeline .

Parameters

pipeline

a GstPipeline

 

Returns

a GstClock, unref after usage.

[transfer full]


gst_pipeline_use_clock ()

void
gst_pipeline_use_clock (GstPipeline *pipeline,
                        GstClock *clock);

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 NULL all clocking will be disabled which will make the pipeline run as fast as possible.

MT safe.

Parameters

pipeline

a GstPipeline

 

clock

the clock to use.

[transfer none][allow-none]

gst_pipeline_auto_clock ()

void
gst_pipeline_auto_clock (GstPipeline *pipeline);

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

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

MT safe.

Parameters

pipeline

a GstPipeline

 

gst_pipeline_set_auto_flush_bus ()

void
gst_pipeline_set_auto_flush_bus (GstPipeline *pipeline,
                                 gboolean auto_flush);

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

pipeline

a GstPipeline

 

auto_flush

whether or not to automatically flush the bus when the pipeline goes from READY to NULL state

 

gst_pipeline_get_auto_flush_bus ()

gboolean
gst_pipeline_get_auto_flush_bus (GstPipeline *pipeline);

Check if pipeline will automatically flush messages when going to the NULL state.

Parameters

pipeline

a GstPipeline

 

Returns

whether the pipeline will automatically flush its bus when going from READY to NULL state or not.

MT safe.


gst_pipeline_set_delay ()

void
gst_pipeline_set_delay (GstPipeline *pipeline,
                        GstClockTime delay);

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

pipeline

a GstPipeline

 

delay

the delay

 

gst_pipeline_get_delay ()

GstClockTime
gst_pipeline_get_delay (GstPipeline *pipeline);

Get the configured delay (see gst_pipeline_set_delay()).

Parameters

pipeline

a GstPipeline

 

Returns

The configured delay.

MT safe.

Types and Values

struct GstPipeline

struct GstPipeline {
  GstClock      *fixed_clock;

  GstClockTime   stream_time;
  GstClockTime   delay;
};

The GstPipeline structure.

Members

GstClock *fixed_clock;

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

 

GstClockTime 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).

 

GstClockTime delay;

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

 

enum GstPipelineFlags

Pipeline flags

Members

GST_PIPELINE_FLAG_FIXED_CLOCK

this pipeline works with a fixed clock

 

GST_PIPELINE_FLAG_LAST

offset to define more flags

 

Property Details

The “auto-flush-bus” property

  “auto-flush-bus”           gboolean

Whether or not to automatically flush all messages on the pipeline's bus when going from READY to NULL state. Please see gst_pipeline_set_auto_flush_bus() for more information on this option.

Flags: Read / Write

Default value: TRUE


The “delay” property

  “delay”                    guint64

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

Flags: Read / Write

Default value: 0

See Also

GstElement, GstBin, GstClock, GstBus