mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-07-03 13:16:04 +00:00
b69033434f
Original commit message from CVS: * docs/design/draft-klass.txt: * docs/design/part-clocks.txt: * docs/design/part-events.txt: * docs/design/part-gstbin.txt: * docs/design/part-gstpipeline.txt: * docs/design/part-messages.txt: * docs/design/part-negotiation.txt: * docs/design/part-overview.txt: * docs/design/part-preroll.txt: * docs/design/part-seeking.txt: * docs/design/part-states.txt: * docs/design/part-streams.txt: Documentation updates.
91 lines
2.7 KiB
Plaintext
91 lines
2.7 KiB
Plaintext
GstPipeline
|
|
-----------
|
|
|
|
A GstPipeline is usually a toplevel bin and provides all of its
|
|
children with a clock.
|
|
|
|
A GstPipeline also provides a toplevel GstBus (see part-gstbus.txt)
|
|
|
|
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.
|
|
|
|
|
|
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:
|
|
|
|
- NULL -> READY:
|
|
- set the bus to non-flushing
|
|
|
|
- READY -> PAUSED:
|
|
- reset the stream time to 0
|
|
|
|
- PAUSED -> PLAYING:
|
|
- Select and a clock.
|
|
- calculate base time using the stream time.
|
|
- set clock and base time on all elements before performing the
|
|
state change.
|
|
|
|
- PAUSED -> PLAYING:
|
|
- calculate the stream time when the pipeline was stopped.
|
|
|
|
- READY -> NULL:
|
|
- set the bus to flushing (when auto-flushing is enabled)
|
|
|
|
|
|
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 the clock of most upstream element that can provide a clock. This
|
|
selection is performed by iterating the element starting from the
|
|
sinks going upstream.
|
|
|
|
* since this selection procedure happens in the PAUSED->PLAYING
|
|
state change, all the sinks are prerolled and we can thus be sure
|
|
that each sink is linked to some upstream element.
|
|
* in the case of a live pipeline (NO_PREROLL), the sink will not
|
|
be prerolled and the selection process will select the clock of
|
|
a more upstream element.
|
|
|
|
- use GstSystemClock, this only happens when no element provides a
|
|
clock.
|
|
|
|
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.
|
|
|
|
|
|
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 if a FLUSHING seek is requested
|
|
- send the seek event to all sinks
|
|
- when a FLUSH seek was performed successfully, the stream_time is set 0 again.
|
|
- restore old state of the pipeline.
|
|
|
|
|
|
|
|
|