mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-19 08:11:16 +00:00
c94f6bf5bf
Original commit message from CVS: * docs/design/draft-push-pull.txt: * docs/design/part-MT-refcounting.txt: * docs/design/part-TODO.txt: * docs/design/part-caps.txt: * docs/design/part-events.txt: * docs/design/part-gstbus.txt: * docs/design/part-gstpipeline.txt: * docs/design/part-messages.txt: * docs/design/part-push-pull.txt: * docs/design/part-query.txt: Some more docs.
105 lines
3.1 KiB
Text
105 lines
3.1 KiB
Text
GstPipeline
|
|
-----------
|
|
|
|
A GstPipeline is usually a toplevel bin an provides all of its
|
|
children with a clock and a bus.
|
|
|
|
The GstPipeline will also collect EOS messages from its children and
|
|
will forward the EOS message to the application when all of the
|
|
sinks are in EOS.
|
|
|
|
The pipeline also calculates the stream time based on the selected
|
|
clock (see part-clocks.txt).
|
|
|
|
The pipeline manages the seek operation for the application.
|
|
|
|
|
|
GstBus
|
|
------
|
|
|
|
The pipeline creates a GstBus and attaches a sync handler to receive
|
|
the EOS events.
|
|
|
|
Since the pipeline subclasses GstBin, all of its children will receive
|
|
the same bus when added to the Gstbin.
|
|
|
|
The application can retrieve the GstBus and integrate it in the
|
|
mainloop or it can just _pop() messages off in its own thread.
|
|
|
|
|
|
State changes
|
|
-------------
|
|
|
|
In addition to the normal state change procedure of its parent class
|
|
GstBin, the pipeline performs the following actions during a state change:
|
|
|
|
- READY -> PAUSED:
|
|
- Select and set a clock.
|
|
|
|
- PAUSED -> PLAYING:
|
|
- calculate the stream time.
|
|
|
|
The GstPipeline will also wait for any async state change to complete before
|
|
proceeding to the next state change. This is usefull for the application because
|
|
it does not have to deal with ASYNC state changes then.
|
|
|
|
|
|
Clock selection
|
|
---------------
|
|
|
|
Since all of the children of a GstPipeline must use the same clock, the
|
|
pipeline must select a clock.
|
|
|
|
The default clock selection algorithm works as follows:
|
|
|
|
- If the application selected a clock, use that clock. (see below)
|
|
- use clock of source elements (*)
|
|
- use clock of other element, starting from the sinks going upstream.
|
|
(+)
|
|
- use GstSystemClock.
|
|
|
|
(*) currently not implemented.
|
|
(+) traversing the graph upstream to find the best clock is not implemented,
|
|
currently the first element found that provides a clock is used.
|
|
|
|
The application can influence this clock selection with two methods:
|
|
gst_pipeline_use_clock() and gst_pipeline_auto_clock().
|
|
|
|
The _use_clock() method forces the use of a specific clock on the pipeline
|
|
regardless of what clock providers are children of the pipeline. Setting
|
|
NULL disables the clock completely and makes the pipeline run as fast as
|
|
possible.
|
|
|
|
The _auto_clock() method removes the fixed clock and reactivates the auto-
|
|
matic clock selection algorithm described above.
|
|
|
|
|
|
EOS
|
|
---
|
|
|
|
The sink elements will post an EOS event on the bus when they reach EOS. The
|
|
EOS message is only posted to the bus when the element is in PLAYING.
|
|
|
|
The pipeline collects all EOS messages and forwards it to the application as
|
|
soon as all the sinks have posted an EOS.
|
|
|
|
The list of queued EOS messages is cleared when the pipeline goes to PAUSED
|
|
again. This means that all elements should repost the EOS message when going
|
|
to PLAYING again.
|
|
|
|
|
|
Seeking
|
|
-------
|
|
|
|
When performing a seek on the pipeline element using gst_element_send_event(),
|
|
the pipeline performs the following actions:
|
|
|
|
- record the current state of the pipeline.
|
|
- set the pipeline to paused
|
|
- send the seek event to all sinks
|
|
- update the stream time with the time of the seek
|
|
- restore old state of the pipeline.
|
|
|
|
|
|
|
|
|