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. It will also implement a default behaviour for managing seek
events (see seek).
Pipeline 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
Before changing the state of the Pipeline (see
Element) a Bus can be retrieved with
get_bus. This bus can then be used to receive
Message from the elements in the pipeline.
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
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 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 SystemClock 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
When sending a flushing seek event to a GstPipeline (see seek), it will make
sure that the pipeline is properly PAUSED and resumed as well as set the new running time to 0 when the seek succeeded.
Last reviewed on 2009-05-29 (0.10.24)