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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.
82 lines
2.5 KiB
Text
82 lines
2.5 KiB
Text
Seeking
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-------
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Seeking in GStreamer means configuring the pipeline for playback of the
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media between a certain start and stop time, called a segment.
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Different kinds of seeking exist:
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- immediate seeking with low latency (FLUSH seek)
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- seeking without flush, playback will start from the new
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position after all the queues are emptied with old data.
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- segment seeking with and without FLUSH, this can be used to
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implement seamless looping or NLE functionality.
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Seeking can be performed in different formats such as time, frames
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or samples.
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Seeking can be performed to an absolute position or relative to the
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current configured segment.
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For seeking to work reliably, all plugins in the pipeline need to follow
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the well-defined rules in this document.
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Non segment seeking will make the pipeline emit EOS when the configured
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segment has been played.
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Segment seeking will not emit an EOS at the end of the range but will
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post a SEGMENT_DONE message on the bus. This message is posted by the
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earliest element in the pipeline, typically a demuxer. After receiving
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the message, the application can reconnect the pipeline or issue other
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seek events in the pipeline. Since the message is posted as early as
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possible in the pipeline, the application has some time to issue a new
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seek to make the transition seemless. Typically the allowed delay is
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defined by the buffer sizes of the sinks as well as the size of any
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queues in the pipeline.
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The seek can also change the playback speed of the configured segment.
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A speed of 1.0 is normal speed, 2.0 is double speed. Negative values
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mean backward playback.
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Generating seeking events
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-------------------------
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The different kinds of seeking methods and their internal workings are
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described below.
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FLUSH seeking
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-------------
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This is the most common way of performing a seek in a playback application.
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The application issues a seek on the pipeline and the new media is immediatly
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played after the seek calls returns.
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seeking without FLUSH
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---------------------
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This seek type is typically performed after issuing segment seeks to finish
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the playback of the pipeline.
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Performing a non-flushing seek in a PAUSED pipeline blocks until the pipeline
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is set to playing again since all data passing is blocked in the prerolled
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sinks.
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segment seeking with FLUSH
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--------------------------
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This seek is typically performed when starting seamless looping.
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segment seeking without FLUSH
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-----------------------------
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This seek is typically performed when continuing seamless looping.
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