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326d36b8d8
Original commit message from CVS: Added state change code. Added/updated docs. Added sink base class, make fakesink extend the base class. Small cleanups in GstPipeline.
50 lines
1.4 KiB
Plaintext
50 lines
1.4 KiB
Plaintext
Preroll
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-------
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A sink element can only complete the state change to PAUSED after a buffer
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has been queued on the input pad or pads. This process is called prerolling
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and is needed to fill the pipeline with buffers so that the transition to
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PLAYING goes as fast as possible with no visual delay for the user.
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After receiving a buffer (or EOS) on a pad the chain/event function should
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wait to render the buffers or in the EOS case, wait to post the EOS
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message.
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Several things can happen that require the preroll lock to be unlocked. This
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include state changes or flush events.
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Committing the state
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--------------------
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When going to PAUSED and PLAYING a buffer should be queued in the pad. We also
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make this requirement for going to PLAYING since a flush event in the PAUSED
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state could unqueue the buffer again.
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The state is commited in the following conditions:
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- a buffer is received on a sinkpad
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- an EOS is received on a sinkpad.
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We require the state change to be commited in EOS as well since an EOS means
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by definition that no buffer is going to arrive anymore.
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Unlocking the preroll
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---------------------
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The following conditions unlock the preroll:
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- a state change
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- a flush event
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Result of the preroll
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---------------------
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After the preroll is unlocked, the element can be in the following states:
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- in a state that disallows it to process the data (flushing, pad inactive)
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- in a state that allows it to process the data.
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