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Original commit message from CVS: * docs/design/part-TODO.txt: * docs/design/part-clocks.txt: * docs/design/part-element-sink.txt: * docs/design/part-events.txt: * docs/design/part-gstpipeline.txt: Updated docs, mostly DISCONT related.
73 lines
2.1 KiB
Text
73 lines
2.1 KiB
Text
GstPipeline
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-----------
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A GstPipeline is usually a toplevel bin an provides all of its
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children with a clock.
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The pipeline also calculates the stream time based on the selected
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clock (see part-clocks.txt).
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The pipeline manages the seek operation for the application.
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State changes
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-------------
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In addition to the normal state change procedure of its parent class
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GstBin, the pipeline performs the following actions during a state change:
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- READY -> PAUSED:
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- Select and set a clock.
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- PAUSED -> PLAYING:
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- calculate the stream time.
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The GstPipeline will also wait for any async state change to complete before
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proceeding to the next state change. This is usefull for the application because
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it does not have to deal with ASYNC state changes then.
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Clock selection
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---------------
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Since all of the children of a GstPipeline must use the same clock, the
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pipeline must select a clock.
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The default clock selection algorithm works as follows:
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- If the application selected a clock, use that clock. (see below)
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- use clock of source elements (*)
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- use clock of other element, starting from the sinks going upstream.
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(+)
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- use GstSystemClock.
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(*) currently not implemented.
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(+) traversing the graph upstream to find the best clock is not implemented,
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currently the first element found that provides a clock is used.
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The application can influence this clock selection with two methods:
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gst_pipeline_use_clock() and gst_pipeline_auto_clock().
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The _use_clock() method forces the use of a specific clock on the pipeline
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regardless of what clock providers are children of the pipeline. Setting
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NULL disables the clock completely and makes the pipeline run as fast as
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possible.
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The _auto_clock() method removes the fixed clock and reactivates the auto-
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matic clock selection algorithm described above.
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Seeking
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-------
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When performing a seek on the pipeline element using gst_element_send_event(),
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the pipeline performs the following actions:
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- record the current state of the pipeline.
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- set the pipeline to paused
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- send the seek event to all sinks
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- when a FLUSH seek is done, the stream_time is set 0 again.
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- restore old state of the pipeline.
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