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100 lines
2.4 KiB
Text
100 lines
2.4 KiB
Text
Query
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-----
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Purpose
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~~~~~~~
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Queries are used to get information about the stream.
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A query is started on a specific pad and travels up or downstream.
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Requirements
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~~~~~~~~~~~~
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- multiple return values, grouped together when they make sense.
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- one pad function to perform the query
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- extensible queries.
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Implementation
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~~~~~~~~~~~~~~
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- GstQuery extends GstMiniObject and contains a GstStructure (see GstMessage)
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- some standard query types are defined below
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- methods to create and parse the results in the GstQuery.
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- define pad method:
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gboolean (*GstPadQueryFunction) (GstPad *pad,
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GstObject *parent,
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GstQuery *query);
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pad returns result in query structure and TRUE as result or FALSE when
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query is not supported.
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Query types
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~~~~~~~~~~~
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- GST_QUERY_POSITION:
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get info on current position of the stream in stream_time.
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- GST_QUERY_DURATION:
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get info on the total duration of the stream.
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- GST_QUERY_LATENCY:
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get amount of latency introduced in the pipeline. (See part-latency.txt)
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- GST_QUERY_RATE:
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get the current playback rate of the pipeline
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- GST_QUERY_SEEKING:
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get info on how seeking can be done
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- getrange, with/without offset/size
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- ranges where seeking is efficient (for caching network sources)
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- flags describing seeking behaviour (forward, backward, segments,
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play backwards, ...)
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- GST_QUERY_SEGMENT:
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get info about the currently configured playback segment.
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- GST_QUERY_CONVERT:
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convert format/value to another format/value pair.
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- GST_QUERY_FORMATS:
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return list of supported formats that can be used for GST_QUERY_CONVERT.
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- GST_QUERY_BUFFERING:
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query available media for efficient seeking (See part-buffering.txt)
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- GST_QUERY_CUSTOM:
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a custom query, the name of the query defines the properties of the query.
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- GST_QUERY_URI:
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query the uri of the source or sink element
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- GST_QUERY_ALLOCATION:
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the buffer allocation properties (See part-bufferpool.txt)
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- GST_QUERY_SCHEDULING:
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the scheduling properties (See part-scheduling.txt)
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- GST_QUERY_ACCEPT_CAPS:
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check if caps are supported (See part-negotiation.txt)
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- GST_QUERY_CAPS:
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get the possible caps (See part-negotiation.txt)
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